Choreography and Diligence

Why microservices by default isn't a great bet.


  • Microservices are better at making problems obvious than solving them.
  • Packages can be a less demanding alternative.

Ad hominem

Paulo Köch -

  • Yelp
    • Big company: ~400 engineers
    • Decade-old monolith, lots of microservices
  • Doist
    • Medium company: ~50 engineers, ~10 backend, ~10 other contributers
    • Decade-old monolith, a few microservices
  • Trust Fractal
    • Small company: ~10 engineers
    • Greenfield, lots of microservices

Messy Monolith


  • Huge codebase
  • Separation of concerns
  • Deploying
  • Scaling
  • Bulkheading


Let's make them impossible!


Engineering is about trade-offs and optimization.

Microservices are: trade-offs


  • Scale to your own needs
  • You're now a distributed system

You can service requests in whichever way you want, but some team you never
heard of can take your service down.

Microservices are: trade-offs


  • Use the right tool for the job
  • Expertise is fragmented

You can use Prolog in your microservice, but debugging is done through

Microservices are: trade-offs


  • Other teams won't impact your internal structure
  • Any externally-visible structure change becomes a coordination concern

Nobody can make your code slow or clunky, but now you need to have a
mailing list of downstream consumers to change your API.

Microservices are: trade-offs


  • Freedom to choose your own philosophy
  • Everyone needs to be onboarded

You can have monoids of endofunctors and algebraic effects, but only the
indoctrinated will help you.

Microservices are: trade-offs


  • Have tight codebases that do one thing right
  • Have many services with various degree of overlap

You can always spin up new services, but eventually some are left running
with no consumers.

Microservices are: hard boundaries

  • The same people and functionality will still be connected.
  • You've gone from razor-thin to concrete-thick boundaries.
  • Conway's law and Inverse Conway maneuvers
  • Teams have their own backlogs and schedules.
  • Everything becomes choreography.

- Everything becomes choreography.


- Everything becomes choreography.

Choreography is the new nightmare.

Moving on

Microservices is linking at the network layer.

How about we try linking at the function level?


Packages are: the classic commodities

  • Scale arbitrarily
  • Harder boundaries than a single codebase
  • Softer boundaries than multiple systems
  • Fully supported and made easy by your ecosystem (hopefully)

Packages are: trade-offs


  • Constrained to the same process space
  • Not a distributed system

Packages are: trade-offs


  • Contained to one ecosystem
  • Expertise is shared and compounded

Packages are: trade-offs


  • Everyone needs to be dilligent about boundaries
  • Chaging APIs in a codebase is a well-solved problem

Packages are: trade-offs


  • You need to comply to some practices
  • Onboarding is much cheaper

Packages are: trade-offs


  • It's hard to understand which part of the codebase should do what
  • There's lots of mature tooling to help you navigate

Modular Monolith!

Modular Monolith


  • Huge codebase
  • Separation of concerns
  • Deploying
  • Scaling
  • Bulkheading


We still need to get out of them.

Modular Monolith: nightmares

Huge codebase

  • Factor parts out to packages
  • Laborious, but easy

Modular Monolith: nightmares

Separation of concerns

  • Be diligent about architecture
  • Laborious, not easy

Modular Monolith: nightmares


  • Focus on package bumps
  • Automatable, and easy

Modular Monolith: nightmares


  • Use per-endpoint process pools
  • Automatable, and easy

Modular Monolith: nightmares


  • Be diligent about process-level globals and in-process dependencies
  • Light-touch, not easy

Modular Monolith: what's not easy

  • Be diligent about architecture
  • Be diligent about process-level globals and in-process dependencies

- Be diligent


- Be diligent

Diligence is the new nightmare.

Engineering is about trade-offs and optimization

Choose the lesser evil

What's easier to optimize in your context?

  • Choreography: go through the motions for all dependencies
  • Diligence: educate and commit yourself and all your peers

Intrinsic complexity isn't removable, only focusable

What makes you think you're not going to make a mess out
of [microservices]?

-- Kevlin Henney, Managing Complexity in Software


Thank you


I've been programming for 15 years, and I've worked in enough different environments with microservices.

A bunch of people wrote a bunch of code, and now they're sad about it.

- Just too much to know, it's nearly impossible to know the whole system.

- Everything's tangled up, there's unrelated wires everywhere because "I need to do an `if` over there", nobody knows where their part of the system ends and others' begin. Even worse, some improvident enterprising soul started using shared mutable state in memory.

- Everyone wants to get in on releases, you're taking very unrelated changes to prod at the same time, there's a lot of waiting for gigantic test suites to pass, a whole new 500MB Docker image needs to go out all servers when you only changed a few bytes, etc.

- Your frontpage is being hammered, you can't bill clients anymore.

- Somebody misconfigures something about taxes, you can't show your homepage anymore.

Microservices help with some things, and get in the way with others.

It's also about feasability, but that doesn't apply to software.

+ You now have different parts of the application with their own databases, web workers, background workers, etc. You can scale precisely to what the customers need from you right now!

- Distributed systems aren't to be taken lightly. They're their own specialization inside backend. If you don't take it seriously, different parts of your system believe in different truths.

- Your store service doesn't work because the inventory service doesn't work.

+ If you have a scheduling problem, you can use Prolog! If you have a CPU-heavy problem, you can use Rust!

- Everyone produces CSV files slightly differenly.

- You're now on call for your microservices. If someone downstream from you is having problems, you now need their help or learn their system. Your dependency tree can be arbitrarily deep.

+ Nobody will feel tempted to pass unrelated information through your code. You control how much impact observability has in your performance.

- Removing a field from an API takes many quarters. Once you start emitting a stream of events in a certain schema, you're potentially locked to it forever.

The reverse is also true: if you want to contribute a change to somebody else's code, you need to learn their customs first.

+ Only one concern, scope creeps start smelling pretty fast.

- Different systems will have different assurances.

- When people can't convince someone to add a feature to some sevice, they might very well fork it and implement that thing in the new fork.

- Eventually, you'll have to adopt governance to decide when to sunset them.

- The problem was "other people" and "code". It's still that.

- It's going from living in a loft to living in a campus.

- Much more tech involved. Don't pay for it unless you're also reaping tech benefits.

- Nobody wants to becomes an expert on distsys, DBs, k8s, and everything.

- You start concentrating competency (both tech and domain) on teams.

- You can outsource to both services and consultancy.

- Microservices shifts the focus to teams and their stewardship.

- It's going from living in a loft to living in an apartment.

- Your store can DoS your homepage.

+ No more timeouts, retries, sagas, or eventual consisteny.

You can still import alien code through JNI, FFI, dynamic libraries, etc. But you're now constrained to your ecosystem. Like Erlang? Too bad! JNI takes a bunch of time on the first run? Too bad! Need to translate the in-memory representation at the boundary? Too bad!

This essentially means there's only a single "language plarform" team.

- It's easier to forgive a dumb argument in a function call than in an HTTP call.

- It's also easier to undo.

In microservices, this was being enforced by other teams.