MMore
I have an Elixir apps which does some harder jobs in the background. I am using Oban to run them asynchrously. For better availability I’d like to spawn a second server instance of my Elixir app (I am using fly.io) but without spawing another Oban app there.
Currently Oban is just part of the Standard Application Supervision Tree:
def start(_type, _args) do
children = [
# Start the Ecto repository
MyApp.Repo,
MyAppWeb.Telemetry,
{Phoenix.PubSub, name: MyApp.PubSub},
MyAppWeb.Endpoint,
{Oban, Application.fetch_env!(:my_app, Oban)}
]
opts = [strategy: :one_for_one, name: MyApp.Supervisor]
Supervisor.start_link(children, opts)
end
Any idea how to do it?
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stefanchrobot
You can:
if ..., do: base_children, else: base_children ++ [{Oban, ...}]),config :my_app, Oban, queues: false, plugins: false).You need to figure out the condition. This can be based on the value of
node()or some ENV var passed during startup.entone
Can’t Oban work across multiple nodes and share the processing load?
MMore
I guess it can. But I have like jobs which need a lot of processing power. So I don’t wanna let them run on my web facing machine which has less power.
sorentwo
There is an official guide on this exact subject: Splitting Queues Between Nodes — Oban v2.23.0
MMore
I see, thank you. My problem is more that all of the machines have the same set of environment variables. So I need to figure out how to start it on the first machine only or have a different set of environment variables.
entone
Interesting, are the FE and BE nodes setup in a distributed Erlang cluster?
sorentwo
The Fly way to do this, AFAIK, is to make separate apps that share a network and a database: Multiple processes inside a Fly.io app · Fly Docs
engineeringdept
You might also consider using Highlander to ensure a process only runs once, globally, in a cluster. I use it for Quantum cron jobs.
sorentwo
Oban already ensures that jobs only run once for the given period across the entire cluster (even across restarts).
You could use leadership to only run those jobs in one node. However, then you can’t scale or control whether those nodes also serve web requests.
engineeringdept
Sorry, didn’t mean to reply directly to you! Oban does a great job of this already, but if you want to run any old process as a singleton globally, Highlander is worth looking at.