Run `rails c` on GCloud instace with appengine gem - ruby-on-rails

Question

I have a Rails 6.0.0.rc1 application (with the appengine gem install) that I deployed to GCP. Is there a way to log into a remote rails console on the instance that runs the application? I tried this:
bundle exec rake appengine:exec -- bundle exec rails c
which gives the following output:
...
---------- EXECUTE COMMAND ----------
bundle exec rails c
Loading production environment (Rails 6.0.0.rc1)
Switch to inspect mode.
...
so apparently it executed the command, but closes the connection right after.
Is there an easy way to do this?
As reference: On Heroku this would simply be:
heroku run rails c --app my-application

Answer 1

There's a few steps involved:
https://gist.github.com/kyptin/e5da270a54abafac2fbfcd9b52cafb61
If you're running a Rails app in Google App Engine's flexible environment, it takes a bit of setup to get to a rails console attached to your deployed environment. I wanted to document the steps for my own reference and also as an aid to others.
Open the Google App Engine -> instances section of the Google Cloud Platform (GCP) console.
Select the "SSH" drop-down for a running instance. (Which instance? Both of my instances are in the same cluster, and both are running Rails, so it didn't matter for me. YMMV.) You have a choice about how to connect via ssh.
Choose "Open in browser window" to open a web-based SSH session, which is convenient but potentially awkward.
Choose "View gcloud command" to view and copy a gcloud command that you can use from a terminal, which lets you use your favorite terminal app but may require the extra steps of installing the gcloud command and authenticating the gcloud command with GCP.
When you're in the SSH session of your choice, run sudo docker ps to see what docker containers are presently running.
Identify the container of your app. Here's what my output looked like (abbreviated for easier reading). My app's container was the first one.
jeff#aef-default-425eaf...hvj:~$ sudo docker ps
CONTAINER ID IMAGE COMMAND NAMES
38e......552 us.gcr.io/my-project/appengine/default... "/bin/sh -c 'exec bun" gaeapp
8c0......0ab gcr.io/google_appengine/cloud-sql-proxy "/cloud_sql_proxy -di" focused_lalande
855......f92 gcr.io/google_appengine/api-proxy "/proxy" api
7ce......0ce gcr.io/google_appengine/nginx-proxy "/var/lib/nginx/bin/s" nginx_proxy
25f......bb8 gcr.io/google_appengine/fluentd-logger "/opt/google-fluentd/" fluentd_logger
Note the container name of your app (gaeapp in my case), and run container_exec bash.
Add ruby and node to your environment: export PATH=$PATH:/rbenv/versions/2.3.4/bin:/rbenv/bin:/nodejs/bin
cd /app to get to your application code.
Add any necessary environment variables that your Rails application expects to your environment. For example: export DATABASE_URL='...'
If you don't know what your app needs, you can view the full environment of the app with cat app.yaml.
bin/rails console production to start a Rails console in the Rails production environment.