Observing Elixir in Production

Summary

Observer, included with Elixir and Erlang’s BEAM, is a WxWidgets interface that connects in real time to running nodes, showing process trees and state while allowing processes to be killed. This guide uses Fly.io to connect a local Observer to production nodes through a release cookie, a WireGuard tunnel, and a helper script. The example is a multi-region Tic-Tac-Toe application in Frankfurt and Los Angeles; a local IEx session joins the remote cluster, and Observer can connect to either node. Inspecting a live game exposes its GenServer state in Erlang representation. Killing its process immediately starts a replacement with a different PID and leaves other games running, but recovery still requires the player to reload the page or restart game joining.

Takeaways

1. 1

   A local Observer instance can connect to Elixir nodes running across Fly regions through a WireGuard tunnel and a shared release cookie.

2. 2

   Observer exposes process trees and GenServer state, with state displayed in Erlang’s representation of Elixir data types.

3. 3

   Killing a game process starts a replacement without affecting other running games, but the player must reload the page or restart game joining to recover.