Failed to start child: ** (EXIT) already started

francois1

I want to share a Finch app among Umbrella apps.

In foo_app:

  def start(_type, _args) do
    children = [
      {Finch, name: MyAppServer.Finch},

In bar_app:

  def start(_type, _args) do
    children = [
      {Finch, name: MyAppServer.Finch},

This leads to the error:

Application bar_app exited: BarApp.Application.start(:normal, ) returned an error: shutdown: failed to start child: MyAppServer.Finch

Is there any way to start the app only if not already available?

Other options:

start it only from one of the apps
=> but what if I want to start the other app (which wouldn’t start Finch) independently
use 2 Finch instances
=> the Swoosh mailer accepts only one Finch instance
start it in a shared app
=> ultimately possible if no other easier solution

5 comments

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2023-10-27 15:47:37 UTC

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benwilson512

Author of Craft GraphQL APIs in Elixir with Absinthe

You aren’t starting an app, you are defining an instance of Finch, monitored in your apps supervision tree, with a name. You’re explicitly starting it twice with the same name.

If you plan to use it from Swoosh and you want just one swoosh config then you should run finch in whatever app is using swoosh. If multiple apps are using swoosh then I would start two finch instances and configure each swoosh to use one.

Ultimately issues like this are why I abandoned umbrella apps. The “you might start parts of it separately” part was always theoretical, and the dependency struggles was always concrete and ever present.

Post #1

francois1

I’d go for this first but swoosh can just have one global configuration, not a config per app inside the umbrella:

The config for Swoosh looks like this:

config :swoosh, :api_client, Something.Finch

Post #2

benwilson512

Author of Craft GraphQL APIs in Elixir with Absinthe

That seems like a major deficiency in swoosh then. Most elixir apps have gone away from singleton configuration for this and other reasons.

Post #3

dimitarvp

I agree with Ben both that (1) umbrella apps are a trap and (2) Swoosh could have done its configuration setup better but having said that, why would you want to have separate API clients for both apps? Why not just one (and maybe give it a bigger connection pool)?

Though it’s not clear from your post how are your apps related (and are they started on separate nodes) so maybe my suggestion is not relevant.

Post #4

francois1

In my case I have apps deployed independently. The reason I went for an Umbrella is that it is a well-documented setup for having one repo with multiple apps and shared dependencies, there is tooling provided such as running all tests from the root, run all apps at once in development, etc.
I could move away from Umbrella easily as those apps are not coupled except that they share some common files. Whether I use Umbrella or not, the alternative will result in nearly the same setup in my opinion… well, I could have configured Swoosh separately if I had totally separated apps without Umbrella.
I do not use Umbrella apps to enforce separation of concerns in code, but only to have a set of independently deployable apps that belong to one same suite of apps.

Deployment is not my forte. What I would do is simply have separate Finch instances and separate Swoosh configs, whether they are deployed on a same node or not, as it is the easiest to set up (i.e. just configure finch/swoosh for every app in the config file copy/paste:)) But again, Swoosh doesn’t allow that.

Post #5

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