Can't connect to an SQLite database with Dokku

I have set show_sensitive_data_on_connection_error to true in runtime.exs, just like it suggested in the error message, and can now see the actual error:

** (MatchError) no match of right hand side value:
  {:error, "attempt to write a readonly database"}

I’ll post an update when I have an answer.

It’s because the user inside the container is not root (good practice). I imagine you have nothing important there yet, so my suggestion is that you delete the file (as root) and recreate from inside the container (as the correct user).

E.g. with mix ecto.setup

(Typing on mobile off the top of my head, there can be mistakes)

Thank you!

I deleted the SQLite file and added database creation to release.ex:

  def migrate do
    load_app()

    # This is what `mix ecto.create` does internally:
    opts = Application.get_env(:myapp, MyApp.Repo)
    MyApp.Repo.__adapter__().storage_up(opts)

    # ....

But, it still couldn’t access. So I added a touch command in app.json (for Dokku)

{
	"scripts": {
		"dokku": {
			"predeploy": "touch /app/storage/wetouched && /app/bin/migrate"
		}
	}
}

remote: touch: cannot touch '/app/storage/wetouched': Permission denied

This makes me think the container is somehow completely immutable at build time. I’ll dive deeper into Dokku documentation, and potentially try using buildpacks instead of Dockerfile.

Oh, you don’t want to create a database during build. The database itself is not to be part of the Docker image.

It will be created/migrated at run time, when replacing the current deploy with the new (after you get the app out to the world…)

My bad for mentioning earlier: the predeploy script actually runs as new container from the built image, not during the build.

This command solved it for me:

chmod a+w /var/lib/dokku/data/storage/myapp

Source and relevant GitHub issue

It was the “permissions” thing all along.

That does it, but makes the database file writable by all users.

A safer option is to use

dokku storage:ensure-directory --chown nobody:nobody myapp

(Assuming USER nobody from phoenix/priv/templates/phx.gen.release/Dockerfile.eex at v1.8.3 · phoenixframework/phoenix · GitHub)

Correcting a small mistake in my previous post – there’s no --chown uid:gid, but instead use --chown false and then manually chown the directory as needed:

APP_NAME=myapp
DIRECTORY_BASENAME=myapp
TARGET_PATH=/mnt/data
CONTAINER_USER_ID=4004
CONTAINER_GROUP_ID=4004
DOKKU_STORAGE_PATH=/var/lib/dokku/data/storage/${DIRECTORY_BASENAME}

dokku storage:ensure-directory --chown false ${DIRECTORY_BASENAME}
dokku storage:mount ${APP_NAME} ${DOKKU_STORAGE_PATH}:${TARGET_PATH}
sudo chown -R ${CONTAINER_USER_ID}:${CONTAINER_GROUP_ID} ${DOKKU_STORAGE_PATH}