Questionable Advice: “What’s the critical path?”

Dan Golant asked a great question today: “Any advice/reading on how to establish a team’s critical path?”

I repeated back: “establish a critical path?” and he clarified:

Yea, like, you talk about buttoning up your “critical path”, making sure it’s well-monitored etc. I think that the right first step to really improving Observability is establishing what business processes *must* happen, what our “critical paths” are. I’m trying to figure out whether there are particularly good questions to ask that can help us document what these paths are for my team/group in Eng.

“Critical path” is one of those phrases that I think I probably use a lot. Possibly because the very first real job I ever had was when I took a break from college and worked at (“we handle the world’s email”) — and by “work” I mean, “lived in SF for a year when I was 18 and went to a lot of raves and did a lot of drugs with people way cooler than me”. Then I went back to college, the dotcom boom crashed, and the CP CFO and CEO actually went to jail for cooking the books, becoming the only tech execs I am aware of who actually went to jail.

Where was I.

Right, critical path. What I said to Dan is this: “What makes you money?”

Like, if you could only deploy three end-to-end checks that would perform entire operations on your site and ensure they work at all times, what would they be? what would they do? “Submit a payment” is a super common one; another is new user signups.servicelevel

The idea here is to draw up a list of the things that are absolutely worth waking someone up to fix immediately, night or day, rain or shine. That list should be as compact and well-defined as possible. This allows you to be explicit about the fact that anything else can wait til morning, or some other less-demanding service level agreement.

And typically the right place to start on this list is by asking yourselves: “what makes us money?” as a proxy for the real questions, which are: “what actions allow us to survive as a business? What do our customers care the absolute most about? What makes us us?” That’s your critical path.

Someone will usually seize this opportunity to argue that absolutely any deterioration in service is worth paging someone immediately to fix it, day or night. They are wrong, but it’s good to flush these assumptions out and have this argument kindly out in the open.

(Also, this is really a question about service level objectives. So if you’re asking yourself about the critical path, you should probably consider buying Alex Hidalgo’s book on SLOs, and you may want to look into the Honeycomb SLO product, the only one in the industry that actually implements SLOs as the Google SRE book defines them (thanks Liz!) and lets you jump straight from “what are our customers experiencing?” to “WHY are they experiencing it”, without bouncing awkwardly from aggregate metrics to logs and back and just … hoping … the spikes line up according to your visual approximations.)

Questionable Advice: “What’s the critical path?”

Observability is a Many-Splendored Definition

Last weekend, @swyx posted a great little primer to instrumentation titled “Observability Tools in JavaScript”.  A friend sent me the link and suggested that I might want to respond and clarify some things about observability, so I did, and we had a great conversation!  Here is a lightly edited transcript of my reply tweet storm.

First of all, confusion over terminology is understandable, because there are some big players out there actively trying to confuse you!  Big Monitoring is indeed actively trying to define observability down to “metrics, logs and traces”.  I guess they have been paying attention to the interest heating up around observability, and well… they have metrics, logs, and tracing tools to sell?  So they have hopped on the bandwagon with some undeniable zeal.

But metrics, logs and traces are just data types.  Which actually has nothing to do with observability.  Let me explain the difference, and why I think you should care about this.

“Observability? I do not think it means what you think it means.”

Mouse Fishbowl Observability 2x2.5

Observability is a borrowed term from mechanical engineering/control theory.  It means, paraphrasing: “can you understand what is happening inside the system — can you understand ANY internal state the system may get itself into, simply by asking questions from the outside?”  We can apply this concept to software in interesting ways, and we may end up using some data types, but that’s putting the cart before the horse.

It’s a bit like saying that “database replication means structs, longints and elegantly diagrammed English sentences.”  Er, no.. yes.. missing the point much?

This is such a reliable bait and switch that any time you hear someone talking about “metrics, logs and traces”, you can be pretty damn sure there’s no actual observability going on.  If there were, they’d be talking about that instead — it’s far more interesting!  If there isn’t, they fall back to talking about whatever legacy products they do have, and that typically means, you guessed it: metrics, logs and traces.

❌ Metrics

Metrics in particular are actually quite hostile to observability.  They are usually pre-aggregated, which means you are stuck with whatever questions you defined in advance, and even when they aren’t pre-aggregated they permanently discard the connective tissue of the request at write time, which destroys your ability to correlate issues across requests or track down any individual requests or drill down into a set of results — FOREVER.

Which doesn’t mean metrics aren’t useful!  They are useful for many things!  But they are useful for things like static dashboards, trend analysis over time, or monitoring that a dimension stays within defined thresholds.  Not observability.  (Liz would interrupt here and say that Google’s observability story involves metrics, and that is true — metrics with exemplars.  But this type of solution is not available outside Google as far as we know..)

❌ Logs

dieunfufilledDitto logs.  When I say “logs”, you think “unstructured strings, written out to disk haphazardly during execution, “many” log lines per request, probably contains 1-5 dimensions of useful data per log line, probably has a schema and some defined indexes for searching.”  Logs are at their best when you know exactly what to look for, then you can go and find it.

Again, these connotations and assumptions are the opposite of observability’s requirements, which deals with highly structured data only.  It is usually generated by instrumentation deep within the app, generally not buffered to local disk, issues a single event per request per service, is schemaless and indexless (or inferred schemas and autoindexed), and typically containing hundreds of dimensions per event.

❓ Traces

Traces?  Now we’re getting closer.  Tracing IS a big part of observability, but tracing just means visualizing events in order by time.  It certainly isn’t and shouldn’t be a standalone product, that just creates unnecessary friction and distance.  Hrmm … so what IS observability again, as applied to the software domain??

As a reminder, observability applied to software systems means having the ability to ask any question of your systems — understand any user’s behavior or subjective experience — without having to predict that question, behavior or experience in advance.

Observability is about unknown-unknowns.

At its core, observability is about these unknown-unknowns.

Plenty of tools are terrific at helping you ask the questions you could predict wanting to ask in advance.  That’s the easy part.  “What’s the error rate?”  “What is the 99th percentile latency for each service?”  “How many READ queries are taking longer than 30 seconds?”prejudice

  • Monitoring tools like DataDog do this — you predefine some checks, then set thresholds that mean ERROR/WARN/OK.
  • Logging tools like Splunk will slurp in any stream of log data, then let you index on questions you want to ask efficiently.
  • APM tools auto-instrument your code and generate lots of useful graphs and lists like “10 slowest endpoints”.

But if you *can’t* predict all the questions you’ll need to ask in advance, or if you *don’t* know what you’re looking for, then you’re in o11y territory.

  • This can happen for infrastructure reasons — microservices, containerization, polyglot storage strategies can result in a combinatorial explosion of components all talking to each other, such that you can’t usefully pre-generate graphs for every combination that can possibly degrade.
  • And it can happen — has already happened — to most of us for product reasons, as you’ll know if you’ve ever tried to figure out why a spike of errors was being caused by users on ios11 using a particular language pack but only in three countries, and only when the request hit the image export microservice running build_id 789782 if the user’s last name starts with “MC” and they then try to click on a particular button which then issues a db request using the wrong cache key for that shard.

Gathering the right data, then exploring the data.

Observability starts with gathering the data at the right level of abstraction, organized around the request path, such that you can slice and dice and group and  look for patterns and cross-correlations in the requests.

To do this, we need to stop firing off metrics and log lines willynilly and be more disciplined.  We need to issue one single arbitrarily-wide event per service per request, and it must contain the *full context* of that request. EVERYTHING you know about it, anything you did in it, all the parameters passed into it, etc.  Anything that might someday help you find and identify that request.

Then, when the request is poised to exit or error the service, you ship that blob off to your o11y store in one very wide structured event per request per service.

highcardinalityIn order to deliver observability, your tool also needs to support high cardinality and high dimensionality.  Briefly, cardinality refers to the number of unique items in a set, and dimensionality means how many adjectives can describe your event.  If you want to read more, here is an overview of the space, and more technical requirements for observability

You REQUIRE the ability to chain and filter as many dimensions as you want with infinitely high cardinality for each one if you’re going to be able to ask arbitrary questions about your unknown unknowns.  This functionality is table stakes.  It is non negotiable.  And you cannot get it from any metrics or logs tool on the market today.

Why this matters.

Alright, this is getting pretty long. Let me tell you why I care so much, and why I want people like you specifically (referring to frontend engineers and folks earlier in their careers) to grok what’s at stake in the observability term wars.

We are way behind where we ought to be as an industry. We are shipping code we don’t understand, to systems we have never understood. Some poor sap is on call for this mess, and it’s killing them, which makes the software engineers averse to owning their own code in prod.  What a nightmare.

Meanwhile developers readily admit they waste >40% of their day doing bullshit that doesn’t move the business forward.  In large part this is because they are flying blind, just stabbing around in the dark.

We all just accept this.  We shrug and say well that’s just what it’s like, working on software is just a shit salad with a side of frustration, it’s just the way it is.

But it is fucking not.  It is un fucking necessary.  If you instrument your code, watch it deploy, then ask “is it doing what I expect, does anything else look weird” as a habit?  You can build a system that is both understandable and well-understood.  If you can see what you’re doing, and catch errors swiftly, it never has to become a shitty hairball in the first place.  That is a choice.

🌟 But observability in the original technical sense is a necessary prerequisite to this better world. 🌟

If you can’t break down by high cardinality dimensions like build ids, unique ids, requests, and function names and variables, if you cannot explore and swiftly skim through new questions on the fly, then you cannot inspect the intersection of (your code + production + users) with the specificity required to associate specific changes with specific behaviors.  You can’t look where you are going.

Observability as I define it is like taking off the blindfold and turning on the light before you take a swing at the pinata.  It is necessary, although not sufficient alone, to dramatically improve the way you build software.  Observability as they define it gets you to … exactly where you already are.  Which of these is a good use of a new technical term?


Do better.

And honestly, it’s the next generation who are best poised to learn the new ways and take advantage of them. Observability is far, far easier than the old ways and workarounds … but only if you don’t have decades of scar tissue and old habits to unlearn.

The less time you’ve spent using monitoring tools and ops workarounds, the easier it will be to embrace a new and better way of building and shipping well-crafted code.

Observability matters.  You should care about it.  And vendors need to stop trying to confuse people into buying the same old bullshit tools by smooshing them together and slapping on a new label.  Exactly how long do they expect to fool people for, anyway?

Observability is a Many-Splendored Definition

Questionable Advice #2: How Do I Get My Team Into Observability?

Welcome to the second installment of my advice column! Last time we talked about the emotional impact of going back to engineering after a stint in management. If you have a question you’d like to ask, please email me or DM it to me on twitter.

Hi Charity! I hope it’s ok to just ask you this… 

I’m trying to get our company more aware of observability and I’m finding it difficult to convince people to look more into it. We currently don’t have the kind of systems that would require it much – but we will in future and I want us to be ahead of the game. 

If you have any tips about how to explain this to developers (who are aware that quality is important but don’t always advocate for it / do it as much as I’d prefer), or have concrete examples of “here’s a situation that we needed observability to solve – and here’s how we solved it”, I’d be super grateful. 

If this is too much to ask, let me know too 🙂 

I’ve been talking to Abby Bangser a lot recently – and I’m “classifying” observability as “exploring in production” in my mental map – if you have philosophical thoughts on that, I’d also love to hear them 🙂


Dear Alex,

Everyone’s systems are broken. Not just yours!

Yay, what a GREAT note!  I feel like I get asked some subset or variation of these questions several times a week, and I am delighted for the opportunity to both write up a response for you and post it for others to read.  I bet there are orders of magnitude more people out there with the same questions who *don’t* ask, so I really appreciate those who do. <3

I want to talk about the nuts and bolts of pitching to engineering teams and shepherding technical decisions like this, and I promise I will offer you some links to examples and other materials. But first I want to examine some of the assumptions in your note, because they elegantly illuminate a couple of common myths and misconceptions.

Myth #1: you don’t need observability til you have problems of scale

First of all, there’s this misconception that observability is something you only need when you have really super duper hard problems, or that it’s only justified when you have microservices and large distributed systems or crazy scaling problems.  No, no no nononono. 

There may come a point where you are ABSOLUTELY FUCKED if you don’t have observability, but it is ALWAYS better to develop with it.  It is never not better to be able to see what the fuck you are doing!  The image in my head is of a hiker with one of those little headlamps on that lets them see where they’re putting their feet down.  Most teams are out there shipping opaque, poorly understood code blindly — shipping it out to systems which are themselves crap snowballs of opaque, poorly understood code. This is costly, dangerous, and extremely wasteful of engineering time.

Observability is like a headlamp for your code.

Ever seen an engineering team of 200, and struggled to understand how the product could possibly need more than one or two teams of engineers? They’re all fighting with the crap snowball.

Developing software with observability is better at ANY scale.  It’s better for monoliths, it’s better for tiny one-person teams, it’s better for pre-production services, it’s better for literally everyone always.  The sooner and earlier you adopt it, the more compounding value you will reap over time, and the more of your engineers’ time will be devoted to forward progress and creating value.

Myth #2: observability is harder and more technically advanced than monitoring

Actually, it’s the opposite — it’s much easier.  If you sat a new grad down and asked them to instrument their code and debug a small problem, it would be fairly straightforward with observability. Observability speaks the native language of variables, functions and API endpoints, the mental model maps cleanly to the request path, and you can straightforwardly ask any question you can come up with. (A key tenet of observability is that it gives an engineer the ability to ask any question, without having had to anticipate it in advance.)

With metrics and logging libraries, on the other hand, it’s far more have to make a bunch of awkward decisions about where to emit various types of statistics, and it is terrifyingly easy to make poor choices (with terminal performance implications for your code and/or the remote data source).  When asking questions, you are locked in to asking only the questions that you chose to ask a long time ago. You spend a lot of time translating the relationships between code and lowlevel systems resources, and since you can’t break down by users/apps you are blocked from asking the most straightforward and useful questions entirely!  

Doing it the old way Is. Fucking. Hard.  Doing it the newer way is actually much easier, save for the fact that it is, well, newer — and thus harder to google examples for copy-pasta. But if you’re saturated in decades of old school ops tooling, you may have some unlearning to do before observability seems obvious to you.

Myth #3: observability is a purely technical solution

To be clear, you can just add an observability tool to your stack and go on about your business — same old things, same old way, but now with high cardinality!

You can, but you shouldn’t.  

These are sociotechnical systems and they are best improved with sociotechnical solutions.  Tools are an absolutely necessary and inextricable part of it.  But so are on call rotations and the fundamental virtuous feedback loop of you build it, you run it.  So are code reviews, monitoring checks, alerts, escalations, and a blameless culture.  So are managers who allocate enough time away from the product roadmap to truly fix deep technical rifts and explosions, even when it’s inconvenient, so the engineers aren’t in constant monkeypatch mode.

I believe that observability is a prerequisite for any major effort to have saner systems, simply because it’s so powerful being able to see the impact of what you’ve done.  In the hands of a creative, dedicated team, simply wearing a headlamp can be transformational.

Observability is your five senses for production.

You’re right on the money when you ask if it’s about exploring production, but you could also use words that are even more basic, like “understanding” or “inspecting”.  Observability is to software systems as a debugger is to software code.  It shines a light on the black box.  It allows you to move much faster, with more confidence, and catch bugs much sooner in the lifecycle — before users have even noticed.  It rewards you for writing code that is easy to illuminate and understand in production.

So why isn’t everyone already doing it?  Well, making the leap isn’t frictionless.  There’s a minimal amount of instrumentation to learn (easier than people expect, but it’s nonzero) and then you need to learn to see your code through the lens of your own instrumentation.  You might need to refactor your use of older tools, such as metrics libraries, monitoring checks and log lines.  You’ll need to learn another query interface and how it behaves on your systems.  You might find yourself amending your code review and deploy processes a bit.  

Nothing too terrible, but it’s all new.  We hate changing our tool kits until absolutely fucking necessary.  Back at Parse/Facebook, I actually clung to my sed/awk/shell wizardry until I was professionally shamed into learning new ways when others began debugging shit faster than I could.  (I was used to being the debugger of last resort, so this really pissed me off.)  So I super get it!  So let’s talk about how to get your team aligned and hungry for change.

Okay okay okay already, how do I get my team on board?

If we were on the phone right now, I would be peppering you with a bunch of questions about your organization.  Who owns production?  Who is on call?  Who runs the software that devs write?  What is your deploy process, and how often does it get updated, and by who?  Does it have an owner?  What are the personalities of your senior folks, who made the decisions to invest in the current tools (and what are they), what motivates them, who are your most persuasive internal voices?  Etc.  Every team is different.  <3

There’s a virtuous feedback loop you need to hook up and kickstart and tweak here, where the people with the original intent in their heads (software engineers) are also informed and motivated, i.e. empowered to make the changes and personally impacted when things are broken. I recommend starting by putting your software engineers on call for production (if you haven’t).  This has a way of convincing even the toughest cases that they have a strong personal interest in quality and understandability. 

Pay attention to your feedback loop and the alignment of incentives, and make sure your teams are given enough time to actually fix the broken things, and motivation usually isn’t a problem.  (If it is, then perhaps another feedback loop is lacking: your engineers feeling sufficiently aligned with your users and their pain.  But that’s another post.)

Technical ownership over technical outcomes

I appreciate that you want your team to own the technical decisions.  I believe very strongly that this is the right way to go.  But it doesn’t mean you can’t have influence or impact, and particularly in times like this. 

It is literally your job to have your head up, scanning the horizon for opportunities and relevant threats.  It’s their job to be heads down, focusing on creating and delivering excellent work.  So it is absolutely appropriate for you to flag something like observability as both an opportunity and a potential threat, if ignored.

If I were in your situation and wanted my team to check out some technical concept, I might send around a great talk or two and ask folks to watch it, and then maybe schedule a lunchtime discussion.  Or I might invite a tech luminary in to talk with the team, give a presentation and answer their questions.  Or schedule a hack week to apply the concept to a current top problem, or something else of that nature.

But if I really wanted them to take it fucking seriously, I would put my thumb on the scale.  I would find myself a champion, load them up with context, and give them ample time and space to skill up, prototype, and eventually present to the team a set of recommendations.  (And I would stay in close contact with them throughout that period, to make sure they didn’t veer too far off course or lose sight of my goals.)

  1. Get a champion.

    Ideally you want to turn the person who is most invested in the old way of doing things — the person who owns the ELK cluster, say, or who was responsible for selecting the previous monitoring toolkit, or the goto person for ops questions — from your greatest obstacle into your proxy warrior.  This only works if you know that person is open-minded and secure enough to give it a fair shot & publicly change course, has sufficiently good technical judgment to evaluate and project into the future, and has the necessary clout with their peers.  If they don’t, or if they’re too afraid to buck consensus: pick someone else.

  2. Give them context.  

    Take them for a long walk.  Pour your heart and soul out to them.  Tell them what you’ve learned, what you’ve heard, what you hope it can do for you, what you fear will happen if you don’t.  It’s okay to get personal and to admit your uncertainties.  The more context they have, the better the chance they will come out with an outcome you are happy with.  Get them worried about the same things that worry you, get them excited about the same possibilities that excite you.  Give them a sense of the stakes. 

    And don’t forget to tell them why you are picking them — because they are listened to by their peers, because they are already expert in the problem area, because you trust their technical judgment and their ability to evaluate new things — all the reasons for picking them will translate well into the best kind of flattery — the true kind.  

  3. Give them a deadline.

    A week or two should be plenty.  Most likely, the decision is not going to be unilaterally theirs (this also gives you a bit of wiggle room should they come back going “ah no ELK is great forever and ever”), but their recommendations should carry serious weight with the team and technical leadership.  Make it clear what sort of outcome you would be very pleased with (e.g. a trial period for a new service) and what reasons you would find compelling for declining to pursue the project (i.e. your tech is unsupported, cost prohibitive, etc).  Ideally they should use this time to get real production data into the services they are testing out, so they can actually experience and weigh the benefits, not just read the marketing copy.

As a rule of thumb, I always assume that managers can’t convince engineers to do things: only other engineers can.  But what you can do instead is set up an engineer to be your champion.  And then just sit quietly in the corner, nodding, with an interested look on your face.

The nuclear option

if you <3 prod,
prod will <3 you back

You have one final option.  If there is no appropriate champion to be found, or insufficient time, or if you have sufficient trust with the team that you judge it the right thing to do: you can simply order them to do something your way.  This can feel squicky. It’s not a good habit to get into.  It usually results in things being done a bit slower, more reluctantly, more half-assedly. And you sacrifice some of your power every time you lean on your authority to get your team to do something.

But it’s just as bad for a leader to take it off the table entirely.

Sometimes you will see things they can’t.  If you cannot wield your power when circumstances call for it, then you don’t fucking have real power — you have unilaterally disarmed yourself, to the detriment of your org.  You can get away with this maybe twice a year, tops. 

But here’s the thing: if you order something to be done, and it turns out in the end that you were right?  You earn back all the power you expended on it plus interest.  If you were right, unquestionably right in the eyes of the team, they will respect you more for having laid down the law and made sure they did the right thing.



Some useful resources:

Questionable Advice #2: How Do I Get My Team Into Observability?

Deploys: It’s Not Actually About Fridays

I just read this piece, which is basically a very long subtweet about my Friday deploy threads.  Go on and read it: I’ll wait.

Here’s the thing.  After getting over some of the personal gibes (smug optimism?  literally no one has ever accused me of being an optimist, kind sir), you may be expecting me to issue a vigorous rebuttal.  But I shan’t.  Because we are actually in violent agreement, almost entirely.

I have repeatedly stressed the following points:

  1. I want to make engineers’ lives better, by giving them more uninterrupted weekends and nights of sleep.  This is the goal that underpins everything I do.
  2. Anyone who ships code should develop and exercise good engineering judgment about when to deploy, every day of the week
  3. Every team has to make their own determination about which policies and norms are right given their circumstances and risk tolerance
  4. A policy of “no Friday deploys” may be reasonable for now but should be seen as a smell, a sign that your deploys are risky.  It is also likely to make things WORSE for you, not better, by causing you to adopt other risky practices (e.g. elongating the interval between merge and deploy, batching changes up in a single deploy)

This has been the most frustrating thing about this conversation: that a) I am not in fact the absolutist y’all are arguing against, and b) MY number one priority is engineers and their work/life balance.  Which makes this particularly aggravating:

Lastly there is some strange argument that choosing not to deploy on Friday “Shouldn’t be a source of glee and pride”. That one I haven’t figured out yet, because I have always had a lot of glee and pride in being extremely (overly?) protective of the work/life balance of the engineers who either work for me, or with me.  I don’t expect that to change.

Hold up.  Did you catch that clever little logic switcheroo?  You defined “not deploying on Friday” as being a priori synonymous with “protecting the work/life balance of engineers”.  This is how I know you haven’t actually grasped my point, and are arguing against a straw man.  My entire point is that the behaviors and practices associated with blocking Friday deploys are in fact hurting your engineers.

I, too, take a lot of glee and pride in being extremely, massively, yes even OVERLY protective of the work/life balance of the engineers who either work for me, or with me.


Because it is BETTER for them.  Because it is part of a deploy ecosystem which results in them being woken up less and having fewer weekends interrupted overall than if I had blocked deploys on Fridays.fire_burn

It’s not about Fridays.  It’s about having a healthy ecosystem and feedback loop where you trust your deploys, where deploys aren’t a big deal, and they never cause engineers to have to work outside working hours.  And part of how you get there is by not artificially blocking off a big bunch of the week and not deploying during that time, because that breaks up your virtuous feedback loop and causes your deploys to be much more likely to fail in terrible ways.

The other thing that annoys me is when people say, primly, “you can’t guarantee any deploy is safe, but you can guarantee people have plans for the weekend.”

Know what else you can guarantee?  That people would like to sleep through the fucking night, even on weeknights.

When I hear people say this all I hear is that they don’t care enough to invest the time to actually fix their shit so it won’t wake people up or interrupt their off time, seven days a week.  Enough with the virtue signaling already.

You cannot have it both ways, where you block off a bunch of undeployable time AND you have robust, resilient, swift deploys.  Somehow I keep not getting this core point across to a substantial number of very intelligent people.  So let me try a different way.

Let’s try telling a story.

A tale of two startups

Here are two case studies.

Company X

Company X is a three-year-old startup.  It is a large, fast-growing multi-tenant platform on a large distributed system with spiky traffic, lots of user-submitted data, and a very green database.  Company X deploys the API about once per day, and does a global deploy of all services every Tuesday.  Deploys often involve some firefighting and a rollback or two, and Tuesdays often involve deploying and reverting all day (sigh).

Pager volume at Company X isn’t the worst, but usually involves getting woken up a couple times a week, and there are deploy-related alerts after maybe a third of deploys, which then need to be triaged to figure out whose diff was the cause.

Company Z

Company Z is a three-year-old startup.  It is a large, fast-growing multi-tenant platform on a large distributed system with spiky traffic, lots of user-submitted data, and a very green house-built distributed storage engine.  Company Z automatically triggers a deploy within 30 minutes of a merge to master, for all services impacted by that merge.  Developers at company Z practice observability-driven deployment, where they instrument all changes, ask “how will I know if this change doesn’t work?” during code review, and have a muscle memory habit of checking to see if their changes are working as intended or not after they merge to master.

Deploys rarely result in the pager going off at Company Z; most problems are caught visually by the engineer and reverted or fixed before any paging alert can fire.  Pager volume consists of roughly one alert per week outside of working hours, and no one is woken up more than a couple times per year.

Same damn problem, better damn solutions.

If it wasn’t extremely obvious, these companies are my last two jobs, Parse (company X, from 2012-2016) and Honeycomb (company Z, from 2016-present).

They have a LOT in common.  Both are services for developers, both are platforms, both are running highly elastic microservices written in golang, both get lots of spiky traffic and store lots of user-defined data in a young, homebrewed columnar storage engine.  They were even built by some of the same people (I built infra for both, and they share four more of the same developers).

At Parse, deploys were run by ops engineers because of how common it was for there to be some firefighting involved.  We discouraged people from deploying on Fridays, we locked deploys around holidays and big launches.  At Honeycomb, none of these things are true.  In fact, we literally can’t remember a time when it was hard to debug a deploy-related change.

Screen Shot 2019-10-28 at 12.04.48 AM

Screen Shot 2019-10-28 at 12.05.04 AM

What’s the difference between Company X and Company Z?

So: what’s the difference?  Why are the two companies so dramatically different in the riskiness of their deploys, and the amount of human toil it takes to keep them up?

I’ve thought about this a lot.  It comes down to three main things.

  1. Observability
  2. Observability-driven development
  3. Single merge per deploy

1. Observability. 

I think that I’ve been reluctant to hammer this home as much as I ought to, because I’m exquisitely sensitive about sounding like an obnoxious vendor trying to sell you things.  😛  (Which has absolutely been detrimental to my argument.)

When I say observability, I mean in the precise technical definition as I laid out in this piece: with high cardinality, arbitrarily wide structured events, etc.   Metrics and other generic telemetry will not give you the ability to do the necessary things, e.g. break down by build id in combination with all your other dimensions to see the world through the lens of your instrumentation.  Here, for example, are all the deploys for a particular service last Friday:

Screen Shot 2019-10-28 at 12.31.12 AM

Each shaded area is the duration of an individual deploy: you can see the counters for each build id, as the new versions replace the old ones,

2. Observability-driven development.

This is cultural as well as technical.  By this I mean instrumenting a couple steps ahead of yourself as you are developing and shipping code.  I mean making a cultural practice of asking each other “how will you know if this is broken?” during code review.  I mean always going and looking at your service through the lens of your instrumentation after every diff you ship.  Like muscle memory.

3.  Single merge per deploy.

The number one thing you can do to make your deploys intelligible, other than observability and instrumentation, is this: deploy one changeset at a time, as swiftly as possible after it is merged to master.  NEVER glom multiple changesets into a single deploy — that’s how you get into a state where you aren’t sure which change is at fault, or who to escalate to, or if it’s an intersection of multiple changes, or if you should just start bisecting blindly to try and isolate the source of the problem.  THIS is what turns deploys into long, painful marathons.

the mental image in my head for observability-driven development: it’s like a headlamp for your code!

And NEVER wait hours or days to deploy after the change is merged.  As a developer, you know full well how this goes.  After you merge to master one of two things will happen.  Either:

  • you promptly pull up a window to watch your changes roll out, checking on your instrumentation to see if it’s doing what you intended it to or if anything looks weird, OR
  • you close the project and open a new one.

When you switch to a new project, your brain starts rapidly evicting all the rich context about what you had intended to do and and overwriting it with all the new details about the new project.

Whereas if you shipped that changeset right after merging, then you can WATCH it roll out.  And 80-90% of all problems can be, should be caught right here, before your users ever notice —  before alerts can fire off and page you.  If you have the ability to break down by build id, zoom in on any errors that happen to arise, see exactly which dimensions all the errors have in common and how they differ from the healthy requests, see exactly what the context is for any erroring requests.

Healthy feedback loops == healthy systems.

That tight, short feedback loop of build/ship/observe is the beating heart of a healthy, observable distributed system that can be run and maintained by human beings, without it sucking your life force or ruining your sleep schedule or will to live.

faithMost engineers have never worked on a system like this.  Most engineers have no idea what a yawning chasm exists between a healthy, tractable system and where they are now.  Most engineers have no idea what a difference observability can make.  Most engineers are far more familiar with spending 40-50% of their week fumbling around in the dark, trying to figure out where in the system is the problem they are trying to fix, and what kind of context do they need to reproduce.

Most engineers are dealing with systems where they blindly shipped bugs with no observability, and reports about those bugs started to trickle in over the next hours, days, weeks, months, or years.  Most engineers are dealing with systems that are obfuscated and obscure, systems which are tangled heaps of bugs and poorly understood behavior for years compounding upon years on end.

That’s why it doesn’t seem like such a big deal to you break up that tight, short feedback loop.  That’s why it doesn’t fill you with horror to think of merging on Friday morning and deploying on Monday.  That’s why it doesn’t appall you to clump together all the changes that happen to get merged between Friday and Monday and push them out in a single deploy.

It just doesn’t seem that much worse than what you normally deal with.  You think this raging trash fire is, unfortunately … normal.

How realistic is this, though, really?

Maybe you’re rolling your eyes at me now.  “Sure, Charity, that’s nice for you, on your brand new shiny system.  Ours has years of technical debt,  It’s unrealistic to hold us to the same standard.”

Yeah, I know.  It is much harder to dig yourself out of a hole than it is to not create a hole deliberatein the first place.  No doubt about that.

Harder, yes.  But not impossible.

I have done it.

Parse in 2013 was a trash fire.  It woke us up every night, we spent a lot of time stabbing around in the dark after every deploy.  But after we got acquired by Facebook, after we started shipping some data sets into Scuba, after (in retrospect, I can say) we had event-level observability for our systems, we were able to start paying down that debt and fixing our deploy systems.

We started hooking up that virtuous feedback loop, step by step.

  1. We reworked our CI/CD system so that it built a new artifact after every single merge.
  2. We put developers at the steering wheel so they could push their own changes out.
  3. We got better at instrumentation, and we made a habit of going to look at it during or after each deploy.
  4. We hooked up the pager so it would alert the person who merged the last diff, if an alert was generated within an hour after that service was deployed.

We started finding bugs quicker, faster, and paying down the tech debt we had amassed from shipping code without observability/visibility for many years.

Developers got in the habit of shipping their own changes, and watching them as they rolled out, and finding/fixing their bugs immediately.

It took some time.  But after a year of this, our formerly flaky, obscure, mysterious, massively multi-tenant service that was going down every day and wreaking havoc on our sleep schedules was tamed.  Deploys were swift and drama-free.  We stopped blocking deploys on Fridays, holidays, or any other days, because we realized our systems were more stable when we always shipped consistently and quickly.  

Allow me to repeat.  Our systems were more stable when we always shipped right after the changes were merged.  Our systems were less stable when we carved out times to pause deployments.  This was not common wisdom at the time, so it surprised me; yet I found it to be true over and over and over again.

This is literally why I started Honeycomb.

When I was leaving Facebook, I suddenly realized that this meant going back to the Dark Ages in terms of tooling.  I had become so accustomed to having the Parse+scuba tooling and being able to iteratively explore and ask any question without having to predict it in advance.  I couldn’t fathom giving it up.

The idea of going back to a world without observability, a world where one deployed and hopethen stared anxiously at dashboards — it was unthinkable.  It was like I was being asked to give up my five senses for production — like I was going to be blind, deaf, dumb, without taste or touch.

Look, I agree with nearly everything in the author’s piece.  I could have written that piece myself five years ago.

But since then, I’ve learned that systems can be better.  They MUST be better.  Our systems are getting so rapidly more complex, they are outstripping our ability to understand and manage them using the past generation of tools.  If we don’t change our ways, it will chew up another generation of engineering lives, sleep schedules, relationships.

Observability isn’t the whole story.  But it’s certainly where it starts.  If you can’t see where you’re going, you can’t go very far.

Get you some observability.

And then raise your standards for how systems should feel, and how much of your human life they should consume.  Do better. 

Because I couldn’t agree with that other post more: it really is all about people and their real lives.

Listen, if you can swing a four day work week, more power to you (most of us can’t).  Any day you aren’t merging code to master, you have no need to deploy either.  It’s not about Fridays; it’s about the swift, virtuous feedback loop.

And nobody should be shamed for what they need to do to survive, given the state of their systems today.

But things aren’t gonna get better unless you see clearly how you are contributing to your present pain.  And congratulating ourselves for blocking Friday deploys is like congratulating ourselves for swatting ourselves in the face with the flyswatter.  It’s a gross hack.

Maybe you had a good reason.  Sure.  But I’m telling you, if you truly do care about people and their work/life balance: we can do a lot better.



Deploys: It’s Not Actually About Fridays

Love (and Alerting) in the Time of Cholera (and Observability)

I made a vow this year to post one blog post a month, then I didn’t post anything at all from May to September.  I have some catching up to do.  😑   I’ve also been meaning to transcribe some of the twitter rants that I end up linking back to into blog posts, so if Graph Everything, Kittensthere’s anything you especially want me to write about, tell me now while I’m in repentance mode.

This is one request I happened to make a note of because I can’t believe I haven’t already written it up!  I’ve been saying the same thing over and over in talks and on twitter for years, but apparently never a blog post.

The question is: what is the proper role of alerting in the modern era of distributed systems?  Has it changed?  What are the updated best practices for alerting?

It’s a great question.  I want to wax philosophically about some stuff, but first let me briefly outline the way to modernize your alerting best practices:

  1. implement observability
  2. implement SLOs and/or end-to-end checks that traverse key code paths and correlate to user-impacting events
  3. create a secondary channel (tasks, ticketing system, whatever) for “things that on call should look at soon, but are not impacting users yet” which does not page anyone, but which on call is expected to look at (at least) first thing in the morning, last thing in the evening, and midday
  4. move as many paging alerts as possible to the secondary channel, by engineering your services to auto-remediate or run in degraded mode until they can be patched up
  5. wake people up only for SLOs and health checks that correlate to user-impacting events

Or, in an even shorter formulation: delete all your paging alerts, then page only on e2e alerts that mean users are in pain.  Rely on debugging tools for debugging, and paging only when users are in pain.

To understand why I advocate deleting all your paging alerts, and when it’s safe to delete them, first we need to understand why have we accumulated so many crappy paging alerts over the years.

Monoliths, LAMP stacks, and death by pagebomb

Here, let’s crib a couple of slides from one of my talks on observability.  Here are the characteristics of older monolithic LAMP-stack style systems, and best practices for running them:


The sad truth is, that when all you have is time series aggregates and traditional monitoring dashboards, you aren’t really debugging with science so much as you are relying on your gut and a handful of dashboards, using intuition and scraps of data to try and reconstruct an impossibly complex system state.

This works ok, as long as you have a relatively limited set of failure scenarios that happen over and over again.  You can just pattern match from past failures to current data, and most of the time your intuition can bridge the gap correctly.  Every time there’s Graph Everything Unicorn 2x2an outage, you post mortem the incident, figure out what happened, build a dashboard “to help us find the problem immediately next time”, create a detailed runbook for how to respond to it, and (often) configure a paging alert to detect that scenario.

Over time you build up a rich library of these responses.  So most of the time when you get paged you get a cluster of pages that actually serves to help you debug what’s happening.  For example, at Parse, if the error graph had a particular shape I immediately knew it was a redis outage.  Or, if I got paged about a high % of app servers all timing out in a short period of time, I could be almost certain the problem was due to mysql connections.  And so forth.

Things fall apart; the pagebomb cannot stand

However, this model falls apart fast with distributed systems.  There are just too many failures.  Failure is constant, continuous, eternal.  Failure stops being interesting.  It has to stop being interesting, or you will die.




Instead of a limited set of recurring error conditions, you have an infinitely long list of things that almost never happen …. except that one time they do.  If you invest your time into runbooks and monitoring checks, it’s wasted time if that edge case never happens again.

Frankly, any time you get paged about a distributed system, it should be a genuinely new failure that requires your full creative attention.  You shouldn’t just be checking your phone, going “oh THAT again”, and flipping through a runbook.  Every time you get paged it should be genuinely new and interesting.

And thus you should actually have drastically fewer paging alerts than you used to.

A better way: observability and SLOs.

Instead of paging alerts for every specific failure scenario, the technically correct answer is to define your SLOs (service level objectives) and page only on those, i.e. when you are going to run out of budget ahead of schedule.  But most people aren’t yet operating at this level of sophistication.  (SLOs sound easy, but are unbelievably challenging to do well; many great teams have tried and failed.  This is why we have built an SLO feature into Honeycomb that does the heavy lifting for you.  Currently alpha testing with users.)

If you haven’t yet caught the SLO religion, the alternate answer is that “you should only page on high level end-to-end alerts, the ones which traverse the code paths that make you money and correspond to user pain”.  Alert on the three golden signals: request rate, latency, and errors, and make sure to traverse every shard and/or storage type in your critical path.

That’s it.  Don’t alert on the state of individual storage instances, or replication, or anything that isn’t user-visible.

(To be clear: by “alert” I mean “paging humans at any time of day or night”.  You might reasonably choose to page people during normal work hours, but during sleepy hours most errors should be routed to a non-paging address.  Only wake people up for actual user-visible problems.)

Here’s the thing.  The reason we had all those paging alerts was because we depended on them to understand our systems.

Once you make the shift to observability, once you have rich instrumentation and the ability to swiftly zoom in from high level “there might be a problem” to identifying specifically what the errors have in common, or the source of the problem — you no longer need to lean on that scattershot bunch of pagebombs to understand your systems.  You should be able to confidently ask any question of your systems, understand any system state — even if you have never encountered it before.

With observability, you debug by systematically following the trail of crumbs back to their source, whatever that is.  Those paging alerts were a crutch, and now you don’t need them anymore.

Everyone is on call && on call doesn’t suck.

I often talk about how modern systems require software ownership.  The person who is writing the software, who has the original intent in their head, needs to shepherd that code out into production and watch real users use it.  You can’t chop that up into multiple roles, dev and ops.  You just can’t.  Software engineers working on highly available systems need to be on call for their code.Graph Unicorn 4_x4_

But the flip side of this responsibility belongs to management.  If you’re asking everyone to be on call, it is your sworn duty to make sure that on call does not suck.  People shouldn’t have to plan their lives around being on call.  People shouldn’t have to expect to be woken up on a regular basis.  Every paging alert out of hours should be as serious as a heart attack, and this means allocating real engineering resources to keeping tech debt down and noise levels low.

And the way you get there is first invest in observability, then delete all your paging alerts and start over from scratch.

It works.  It really does. 🌈



Love (and Alerting) in the Time of Cholera (and Observability)