Collecting metrics from plausible (with Prometheus)

[digital88]

Hello.

Does plausible have a way to grab internal metrics with tools like Prometheus? I see some metrics generation code here https://github.com/plausible/analytics/blob/master/lib/plausible/telemetry/plausible_metrics.ex

I tried to make a GET request to /metrics endpoint (usually the "default" way of getting metrics from services) but got "Service Unavailable". Is there a way to get metrics from self-hosted instance?

[ruslandoga]

👋 @digital88

I think you'd need to enable PromEx by setting PROMEX_DISABLED=false in your env vars.

[ruslandoga]

Related:

• you can cross reference Plausible.PromEx against PromEx docs to see what's available
• PromEx.Plug doesn't have :path set, so it'll default to /metrics as expected

[digital88]

Thanks, I'll try! Is there any way to "hot-reload" PROMEX_DISABLE env var in running container? Maybe with /bin/palusible remote ?

[ruslandoga]

It's complicated :) I think it's easier to recreate the container.

[ruslandoga]

Ah, no. There is an easy way but I don't know about all the ⚠️ implications ⚠️ of restarting the application this way.

I've enabled https://who.edify.space/metrics within the running container by setting the env var and then calling :init.restart

$ cd hosting
$ docker compose exec plausible bin/remote

iex(plausible@26dacc616641)1> System.put_env("PROMEX_DISABLED", "false")
:ok
iex(plausible@26dacc616641)2> :init.restart
:ok
# *** ERROR: Shell process terminated! (^G to start new job) ***

That error is expected since IEx (interactive Elixir) is also restarted.
Press ctrl+c twice to exit the "dead" IEx console and check if /metrics is enabled.

---

$ docker ps --filter name=hosting-plausible-1
CONTAINER ID   IMAGE                        COMMAND                  CREATED       STATUS       PORTS                      NAMES
26dacc616641   plausible/analytics:v2.0.0   "/entrypoint.sh sh -…"   2 weeks ago   Up 2 weeks   127.0.0.1:8000->8000/tcp   hosting-plausible-1

Docker didn't notice the restart since the application was restarted within the same Erlang BEAM process.

[digital88]

I just tried this on staging, with container restart. Yes, it works. I will probably just restart my prod container too. Thanks again for help!

Btw, it's such a great feature, why its not documented here https://plausible.io/docs/self-hosting-configuration ? :)