How to exclude a dependency's application from running but still Include it in the Release

I think an included application does what you describe. Roughly, in project A’s mix.exs, you want to set runtime: false for the dependency to B, then update your application config:

  def application do
    [
      mod: {A.Application, []},
      included_applications: [:b],
      extra_applications: [:c, :d] # dependencies of :b that must be started for it to work
    ]
  end

The release will then include :b but not automatically start it. Note that if you have :b as a dependency elsewhere, that may cause it to start regardless - you need to add runtime: false there as well, in that case.
Hope that helps

That worked brilliantly!

I updated deps as follows:

  defp deps do
    [
      # ...
      {:a, github: "c/a", branch: "main", runtime: false}
    ]
  end

and application by:

  def application do
    [
      mod: {A.Application, []},
      included_applications: [:b],
      extra_applications: [:logger, :runtime_tools, :os_mon]
    ]
  end

In my case, I didn’t need to add anything to extra_applications because I was only using one simple module from B , which didn’t require any additional applications.