Hi,
Based on https://elixir-lang.org/getting-started/mix-otp/task-and-gen-tcp.html example, I am writing small websocket server. No Phoenix or Cowboy, just low level Elixir, Task.Supervisor and :gen_tcp. All the protocols are ready/tested so I have very lean and agile PubSub server without all the overlays.
When I use Distillery, generate 0.1.0, start the server, then generate 0.1.1 and upgrade, all the existing connection tasks are killed, which is not optimal with long living tasks/tcp connections with websocket protocol.
I am aware that GenServer offers some automation during upgrade but I don’t know yet if it kills the processes too and migrates data to new version or does some other magic – didn’t rewrite my connection tasks into GenServer and would love to avoid that, plus I am not sure if that would preserve existing connections.
It would save me some time if some kind soul can answer few questions 
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Using Distillery upgrade process, if I rewrite existing tasks into GenServers, would they retain existing websocket connections?
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What happens (low level) during upgrade? Are there messages swishing around or processes just get killed?
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Is there any chance to keep using tasks (not even Agents) to serve websockets and write them in a way to survive upgrade process? It is perfectly OK for existing tasks to keep running until user closes connection and use new version for all new connections – just no idea how to do it.
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How do I pack or invoke :observer with production build using Distillery? Having observer to see what’s actually going on during update would help a lot.
Thank you!
