Crickets, eh? Alright, I’ll post one. Here’s part of a supervision tree from an application I’ve been looking at, built by @alexgaribay.

         ┌────────────────────────┐
         │ Streams RootSupervisor │
         │     (one_for_all)      │
         └────────────────────────┘
                      │
              ┌───────┴─────────────────────┐
              ▼                             ▼
  ┌──────────────────────┐      ┌───────────────────────┐
  │ Stream Info Fetcher  │      │  Streams Supervisor   │
  │                      │      │(dynamic, one_for_one) │
  └──────────────────────┘      └───────────────────────┘
                                            │
                     ┌──────────────────────┴───────────────────────┐
                     ▼                                              ▼
           ┌──────────────────┐                           ┌──────────────────┐
           │Stream Supervisor │                           │Stream Supervisor │
           │  (one_for_all)   │                           │  (one_for_all)   │
           └──────────────────┘                           └──────────────────┘
                     │                                              │
          ┌──────────┴──────────┐                        ┌──────────┴──────────┐
          │                     │                        │                     │
          ▼  GenStage Pipeline  ▼                        ▼  GenStage Pipeline  ▼
┌──────────────────┐  ┌──────────────────┐     ┌──────────────────┐  ┌──────────────────┐
│  Stream Fetcher  │  │ Stream Processor │     │  Stream Fetcher  │  │ Stream Processor │
└──────────────────┘  └──────────────────┘     └──────────────────┘  └──────────────────┘

There are multiple incoming streams of data that need to be processed. We don’t know exactly what those streams are when the application boots.

StreamsRootSupervisor starts one Stream Info Fetcher, which makes a network request and gets back a list of the streams. Stream Info Fetcher tells Streams Supervisor to start one Stream Supervisor for each stream we need to process. This is why Streams Supervisor is “dynamic” - we start its children as we discover that we need them.

Each Stream Supervisor is in charge of making sure one stream of data is processed. To that end, it starts a Stream Fetcher to pull down data for that stream and a Stream Processor to process it, with the two connected in a GenStage pipeline.

Those are all the parts. Regarding supervision strategies:

• At the top, Streams RootSupervisor uses one_for_all because its two children depend on one another; if one crashes, they both need restarting.
• Streams Supervisor uses one_for_one because each stream is processed independently; if one crashes, the others should carry on.
• Stream Supervisor uses one_for_all because a Stream Fetcher and its Stream Processer are useless without each other; if one crashes, they both need restarting.

Note that once Stream Info Fetcher has done its work at boot time, it’s no longer needed and terminates. This doesn’t trigger StreamsRootSupervisor to restart all its children unless Stream Info Fetcher actually crashes; because Stream Info Fetcher is :transient; it’s expected to terminate normally and not be restarted.

Great idea for a thread! Yes, Elixir in Action rocks!

I wrote this a couple of years ago. Here’s my diagram with fun colors!

hangman%20supervision%20tree-12200×1700 205 KB

Parallel hangman game play works by spinning up pairs of player workers and game servers (which talk to each other). The rest of the process tree is mostly administrative support. There’s more diagrams below on the github.. I didn’t get around to diagramming the GenStage dictionary ingestion pipelines.

https://github.com/brpandey/hangman

Thanks for creating this topic! I think it’s a discussion that will be very enlightening for all involved.

I know that it is not quite what you want but I really like ElixirConf 2016 - Selling Food With Elixir by Chris Bell which has a great description of how they split up setup their OTP architecture (and that link goes to that portion of the talk). I especially find it cool how their design mirrors their business domain.