Investigated why all three prop pods were restart-looping every few
minutes (RESTARTS counts 7–11 in 99m). The trail:
20:53:33.058 [error] Postgrex.Protocol ("db_conn_10") disconnected:
client (:"Elixir.Microwaveprop.PromEx.Poller.5000") timed out
because it queued and checked out the connection for longer than
15000ms
PromEx's Oban queue-depth poller was scanning the oban_jobs table
every 5s and holding an Ecto connection past its checkout timeout.
That starved the rest of the pool, so /health's `SELECT 1` couldn't
acquire a connection inside the 3s liveness probe timeout, the
kubelet's failureThreshold=3 tripped, and SIGKILL landed on the
BEAM. Every replica cycled on the same cadence.
Two fixes:
1. Split /live (no DB) from /health (DB ping). Kubernetes livenessProbe
now points at /live so a saturated Ecto pool can never cascade into
SIGKILL. Readiness still hits /health so a genuine DB outage drains
the pod from Service endpoints gracefully.
2. Turn off the PromEx Oban plugin in prod via the same flag already
used in test. The queue-depth query isn't worth pod instability;
the oban_web dashboard surfaces the same information without
scanning the job table on a timer.
Locked both down with HealthController tests that verify /live never
touches the Repo (no sandbox owner, controller.live/2 called directly,
200 ok) and /health does (sanity query round-trips).
