Mix.Task not available in prod releases

Questions / Help
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1

I am trying to reload the config (after programmatically changing the environment) via

Mix.Task.run("loadconfig")

which works fine via iex -S mix but fails after prod release:

$ env MIX_ENV=prod mix release
$ _build/prod/rel/pubsub_elixir/bin/pubsub_elixir start
[...]
    ** (EXIT) an exception was raised:
        ** (UndefinedFunctionError) function Mix.Task.run/1 is undefined (module Mix.Task is not available)
            Mix.Task.run("loadconfig")
[...]

Similar when I call Mix.Tasks.Loadconfig.run([]) directly.

What am I doing wrong?

2

Mix is not available in built release. It is simply not there at all.

3

Thanks, makes sense. Is there another way to “reload” the config after env-var changes?

4

Hey @fergusg welcome! Given that changes to the environment can change an enormous amount about how the application runs (like how it connects to a database, etc) config changes are basically re-deploys. You would normally go about whatever the normal redeploy behavior is to ensure minimal downtime.

5

The background context is that I am trying to deploy as a Docker image in AWS/ECS and loading the env via the AWS Secrets Manager at runtime (so I can use the same image for prod/test/stage etc)

There are alternatives though, I think… I will investigate

Thanks for your reply.

6

if you are using Phoenix and Ecto you mostly provide that via an ENV variable like explained here instead of elixir Config. (see the init/2 part)

This can be “copied” over and used by your own code as needed with different ENV variable names.

I’ve also used/still using this kind of setup and see changes to these ENV vars indeed as a new deploy as described by benwilson above.

7

In my case using neither Phoenix nor Ecto, just plain Elixir. I think a solution is to explicitly pass in the envs as docker arguments (or the AWS/ECS equivalent) rather than trying to load at runtime inside the app.

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