In this article I will go over how to deploy a Livebook App with Smart Remote Execution cells that connect to a Fly.io deployed Phoenix App.

To start, this article assumes two things:

1. You have a Fly.io deployed Phoenix Application
2. You want to deploy a Livebook App to Fly.io that executes code remotely on the deployed Phoenix Application

You can also see these steps in this GitHub gist.

Configuring Phoenix App

There’s a couple things needed to get the Phoenix Application set up to accept connections.

The first is a RELEASE_COOKIE that does not change between deployments and the second is a reliable RELEASE_NODE name. These will be used by Livebook in order to connect and execute code remotely so make sure to note them down somewhere you can access them again.

Take care not to expose these values in source code at all though as they could allow unexpected connections to your node.

1. Generate a cookie
   • In an iex shell run Base.url_encode64(:crypto.strong_rand_bytes(40))
2. Set the cookie value in Fly.io
   • Run fly secrets set RELEASE_COOKIE=$COOKIE
3. Ensure RELEASE_NODE is set in rel/env.sh.eex
   • This should be set to something like "${FLY_APP_NAME}@${FLY_PRIVATE_IP}"
   • If you do not have this, run fly launch to have fly generate it for you, make sure it generates based on existing configuration
4. Deploy the application so the RELEASE_NODE and RELEASE_COOKIE are used
   • Run fly deploy
5. Get the node’s name by starting a remote iex session and taking the value within the iex prompt brackets
   • Run fly ssh console --pty -C "/app/bin/$APP_NAME remote"
   • Take the value within the iex prompt brackets

Deploying Livebook App

Now the Livebook you wish to deploy as an App will need to have some configuration added in order to enable it to connect to the Fly.io deployed Phoenix App.

1. Update Smart Remote Execution cell to get NODE and COOKIE values from ENV secrets
2. Generate Dockerfile with clustering set to Fly.io
3. Save Dockerfile beside livemd file
4. Run fly launch --no-deploy to generate config for Livebook App on Fly.io
5. Set ENV Smart Remote Execution cell secrets in Fly.io, these will be the name of the ENV secret in Livebook prefixed with LB_
   • Run fly secrets set LB_$COOKIE_SECRET_NAME=$COOKIE
   • Run fly secrets set LB_$NODE_SECRET_NAME=$NODE_NAME
6. Set the Livebook password, it must be 12+ characters
   • Run fly secrets set LIVEBOOK_PASSWORD=$PASSWORD
7. Deploy with fly deploy
8. Visit the output URL with /apps appended to it!

And voilà! With this you should be able to access your Livebook App and have it successfully execute code on the remote Node.

Note: If you are saving the Dockerfile to GitHub, you might want to consider removing the potentially sensitive values from it such as the LIVEBOOK_COOKIE and LIVEBOOK_SECRET_KEY_BASE and setting those as secrets in Fly.io as well.

Conclusion

Getting things connected is really simple once you know all the steps. It took me quite a long time to figure this out and get everything in place, especially as the Livebook ecosystem has changed substantially since the Fly.io docs were written.

If you want to read the source material for this check out Fly.io’s connect to Livebook doc, Fly.io’s do interesting things with Livebook doc, and this thread I started asking for help!

2024-01-26