How to connect and debug Elixir or Phoenix App at Heroku?

Heroku has a great feature called heroku ps:exec which allows you to connect to running nodes. You can use this command to connect your elixir nodes easily. And debug your nodes like in your network.

Step 1

Let's start with Procfile To run a named app at heroku your procfile should specify the app name like:

web: MIX_ENV=prod elixir --sname coolelixirapp -S mix run --no-halt

If you are using Phoenix framework:

web: MIX_ENV=prod elixir --sname coolelixirapp -S mix phx.server

Step 2

Deploy your app with one of these Procfiles depending on your app type.

Step 3

On your local:

$ heroku config # list your heroku app configs
$ heroku ps:exec # --dyno=web.1 # will connect you to web1 dyno

Note: heroku ps:exec command does not export your configs to the heroku bash shell. So you will need to export them by yourself.

Step 4

Now you are in Heroku bash shell for web.1 dyno:

$ # You may need to export env vars which listed in previous 'heroku config' execution. 
$ export DATABASE_URL=postgres://username:password@hostname:5432/dbname;
$ export DATABASE_POOL_SIZE=1;
$ # .... Do your all necessary exports
$ MIX_ENV=prod iex --sname coolelixirconsole -S mix # Run a console app

Step 5

Now you are in Elixir console with app name coolelixirconsole:

>> iex(coolelixirconsole@hostname)1> Node.ping :"coolelixirapp@hostname"
>>> :pong # We are connected to our running Elixir node from heroku ps:exec console
>> iex(coolelixirconsole@hostname)2> Node.list
>>> [:"coolelixirapp@hostname"] # As expected it is in the list
>> iex(coolelixirconsole@hostname)3> # Now you can tell what to do to your app as in your network.

savekirk/2017-10-21-how-to-connect-and-debug-elixir-or-phoenix-app-at-heroku.md