Rails Issues with Buildpacks

[eric-hemasystems]

I'm hoping this is the right place to ask this. I've got a Rails app using the older runtimes (based on Ubuntu 16) prior to the introduction of the buildpacks. My app needs a few libraries installed which previously were installed via the runtime_config.packages key in the app.yaml file.

There are a handful of libraries that come pre-packaged with the new runtime but the docs basically say if you need anything more than that you have to use a custom runtime and build your own Dockerfile.

But then this page explains a bit of how to maybe extend the GAE runtime with additional packages instead of making my own Dockerfile from scratch which looks appealing. I have worked at it a good bit and it's almost going. The two issues I have noticed are:

Missing libpq-dev

This is one of the default libraries listed on the default runtime doesn't seem to be already installed if I build my own from gcr.io/buildpacks/builder:google-22. Is that expected? It's not a big deal as I can just add libpq-dev with my own packages I'm installing and it seems to work. But it made me wonder if I'm building fro the right base image.

assets:precompile Is Always in Production Env

The bigger issue is when my assets are pre-compiled it fails because the RAILS_MASTER_KEY doesn't match with the following error:

Running "bundle exec ruby bin/rails assets:precompile (RAILS_ENV=production MALLOC_ARENA_MAX=2 RAILS_LOG_TO_STDOUT=true LANG=C.utf8)"
Step #14 - "build-app": [builder] rails aborted!
Step #14 - "build-app": [builder] ActiveSupport::MessageEncryptor::InvalidMessage: ActiveSupport::MessageEncryptor::InvalidMessage (ActiveSupport::MessageEncryptor::InvalidMessage)
Step #14 - "build-app": [builder] /workspace/config/environment.rb:5:in `<main>'
Step #14 - "build-app": [builder] 
Step #14 - "build-app": [builder] Caused by:
Step #14 - "build-app": [builder] OpenSSL::Cipher::CipherError: OpenSSL::Cipher::CipherError
Step #14 - "build-app": [builder] /workspace/config/environment.rb:5:in `<main>'
Step #14 - "build-app": [builder] Tasks: TOP => assets:precompile => environment
Step #14 - "build-app": [builder] (See full trace by running task with --trace)
Step #14 - "build-app": [builder] Done "bundle exec ruby bin/rails assets:precompile (RAILS_ENV=prod..." (9.448189521s)

The reason for the mismatch is this is not my production environment because it is my staging env. I have tried passing -e RAILS_ENV=staging to pack build but no luck. I believe here it seems to be hard-coded to the production env and I don't see how to override.

Also I find it wild that it continues with the build even though the assets failed. I would have expected it to break the build.