everzet
Elixir 1.9 releases and runtime config file on disk rationale
Hi everyone.
I’ve been reading about the upcoming releases feature in 1.9. In the runtime configuration section, there is one paragraph that caught my attention. It basically suggests that the release in production is going through the following steps on boot:
- Erlang system starts in limited mode, without booting core app supervision tree
- Registered config providers are used to aggregate and merge configs into one big set
- Config set is stored on disk under the RELEASE_TMP directory
- Erlang system reboots in full mode, reads the config file and boots app supervision tree
If this is correct, I have a question. Why the file interaction? Why can’t we start a lightweight GenServer process or an agent within Beam and use it to store and retrieve the runtime configuration instead?
Can somebody please point me in direction of context I am missing? 
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josevalim
We can’t because the configuration is used to configure the system itself, at its core. So you can think that, at the moment the configuration is read, a GenServer isn’t even a thing yet.
everzet
Thank you for sticking with me on this one Very much appreciate your time and patience.
josevalim
Yes!!!
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