[RTC-345] Introduce JF dedicated env vars for running in a distributed mode

[mickel8]

This PR introduces our own env variables for running JF in a cluster.

When we run erlang/elixir locally, we can setup distribution using flags like --sname --name --cookie etc. However, when we make a release, we are provided with special env variables e.g. RELEASE_NODE RELEASE_COOKIE etc. which results in multiple configuration options depending on environment we run Jellyfish in.

Intoducing our own env vars we:

• unify how JF is configured
• have better env names e.g. JF_COOKIE instead of strange RELEASE_COOKIE
• make future documentation easier to understand as our env vars are always available and always the same. RELEASE_* vars are only available after doing mix release so this would add unnecessary complexity in the documentation
• we also follow livebook behaviour, see this PR https://github.com/livebook-dev/livebook/pull/1672

[codecov[bot]]

Codecov Report

Merging #92 (27f163c) into main (5888e33) will decrease coverage by 0.90%. Report is 1 commits behind head on main. The diff coverage is 60.71%.

@@            Coverage Diff             @@
##             main      #92      +/-   ##
==========================================
- Coverage   84.27%   83.37%   -0.90%     
==========================================
  Files          44       44              
  Lines         744      764      +20     
==========================================
+ Hits          627      637      +10     
- Misses        117      127      +10     

Files	Coverage Δ
lib/jellyfish/config_reader.ex	100.00% <100.00%> (ø)
lib/jellyfish/application.ex	36.84% <21.42%> (-43.16%)	:arrow_down:

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[mickel8]

JF_DIST_ENABLED -> no change JF_NODE_NAME -> JF_DIST_NODE_NAME JF_COOKIE -> JF_DIST_COOKIE JF_NODES -> JF_DIST_NODES

@sgfn Can do that but what about WebRTC or RTSP? I think we should prefix them too

[sgfn]

@sgfn Can do that but what about WebRTC or RTSP? I think we should prefix them too

Yeah, I've no problem with that, we should go for it

[roznawsk]

+1 from for comments from @sgfn - other than that LGTM

[mickel8]

Approved, with one small note:

Regarding the .env.sample file: I'm still firmly against making the core Jellyfish documentation spread out in two or more >places -- could you just confirm we will duplicate all of this info in the docs, and not have the docs say: "for more info, >refer to the .env.sample file"?

Sure, I will revisit this once I write official docs