Support Config Providers

[axelson]

Environment

• Elixir version (elixir -v): Elixir 1.12.1 (compiled with Erlang/OTP 24)
• Nerves environment:

mix nerves.env --info

jason@jdesktop ~/d/v/fw (next-release-hex)> mix nerves.env --info ==> nerves ==> fw |nerves_bootstrap| Environment Package List

Pkg: nerves_system_br
Vsn: 1.16.0
Type: system_platform
BuildRunner: {nil, []}

Pkg: nerves_toolchain_ctng
Vsn: 1.8.3
Type: toolchain_platform
BuildRunner: {nil, []}

Pkg: nerves_system_vultr
Vsn: 0.13.0
Type: system
BuildRunner: {Nerves.Artifact.BuildRunners.Local, []}

Pkg: nerves_toolchain_x86_64_nerves_linux_musl
Vsn: 1.4.2
Type: toolchain
BuildRunner: {Nerves.Artifact.BuildRunners.Local, []}

|nerves_bootstrap| Loadpaths Start

Nerves environment
MIX_TARGET: vultr
MIX_ENV: prod

|nerves_bootstrap| Environment Variable List
target: vultr
toolchain: /home/jason/.local/share/nerves/artifacts/nerves_toolchain_x86_64_nerves_linux_musl-linux_x86_64-1.4.2
system: /home/jason/.local/share/nerves/artifacts/nerves_system_vultr-portable-0.13.0
app: .

|nerves_bootstrap| Loadpaths End

• Additional information about your host, target hardware or environment that
  may help
  • deploying to vultr.com cloud compute server

Current behavior

When a Config.Provider is added to the project then there is a message that the environment variable RELEASE_SYS_CONFIG could not be fetched:

Note that the line in the output that starts with provider (provider.ex:219) is a line that I added to elixir for debugging

Expected behavior

The config provider runs successfully and the config it returns is merged.

Thoughts

RELEASE_SYS_CONFIG is supposed to point to the sys.config file which does exist, so a possible fix could be to simply set the environment file. But I'm not sure where in nerves it should be set and I'm not sure if there's a good reason not to set it.

Relevant docs:

RELEASE_SYS_CONFIG - the location of the sys.config file. It can be set to a custom path and it must not include the .config extension
https://hexdocs.pm/mix/master/Mix.Tasks.Release.html

I have not yet tried to reproduce this on other nerves systems, but I suspect that the same error would appear.

[fhunleth]

Support would need to be added to erlinit, but I wonder why Elixir can't figure this out itself since the sys.config is in the release that it makes.

Out of curiosity, what would be a use for a config provider?

[axelson]

My use case for the config provider is to store secrets on the device in a file instead of in the git repository. And potentially to even use something like etcd in the future.

[fhunleth]

I realized that erlinit already lets you set arbitrary environment variables, so you can do this today:

config :nerves, :erlinit, env: "RELEASE_SYS_CONFIG=path"

[axelson]

Thanks! I just confirmed that this works 🎉:

config :nerves, :erlinit, env: "RELEASE_SYS_CONFIG=/srv/erlang/releases/0.1.0/sys"

(although with the downside that if I update my app's version I'll have to update this configuration line)

[fhunleth]

It's possible for erlinit to add this line automatically.

I'm still confused as to why RELEASE_SYS_CONFIG is needed, since it seems like it should be possible to figure out automatically. There aren't any requirements for the directory to be writable, are there?

I suppose that even if there are caveats to erlinit setting this automatically, the caveats aren't as confusing as the current state where it isn't set at all. Right?

[axelson]

I'm still confused as to why RELEASE_SYS_CONFIG is needed, since it seems like it should be possible to figure out automatically. There aren't any requirements for the directory to be writable, are there?

I haven't looked into the details of the release process to be knowledgeable to answer this, but I wouldn't think that the directory needs to be writeable.

I suppose that even if there are caveats to erlinit setting this automatically, the caveats aren't as confusing as the current state where it isn't set at all. Right?

I don't forsee any caveats (famous last words!) and I would expect that a user would be able to overwrite the RELEASE_SYS_CONFIG setting similar to how I showed above if it is necessary for some reason.

[fhunleth]

@axelson I had to add RELEASE_ROOT for runtime.exs to work for me. Did you have to do this? Were there any other variables that needed to be defined for you?

[axelson]

@fhunleth I did not have to add RELEASE_ROOT, although I'm using this with https://github.com/nerves-project/nerves_system_vultr
The only relevant change I have is:

 config :nerves,
   erlinit: [
-    hostname_pattern: "nerves-%s"
+    hostname_pattern: "nerves-%s",
+    # Workaround for https://github.com/nerves-project/nerves/issues/632
+    env: "RELEASE_SYS_CONFIG=/srv/erlang/releases/0.1.0/sys"
   ]

[fhunleth]

Thanks. Then nerves-project/erlinit#88 will fix the issue that you ran into. It will be in nerves_system_br 1.16.4.

[axelson]

Fantastic, thank you!