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fix/observability: Prometheus read only root volume - #1479
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marcleblanc2
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November 11, 2026 03:59
The prometheus image now keeps Alertmanager's configuration and state on the /prometheus data volume, so nothing writes to the root filesystem. Needs sourcegraph/sourcegraph#18737 in the pinned image. Amp-Thread-ID: https://ampcode.com/threads/T-01a13cfb-9756-7111-8b29-381a841065e1 Co-authored-by: Amp <amp@ampcode.com>
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Problem
Some customers need a read-only root filesystem on every container, and still need Alertmanager to work
The
prometheusservice couldn't beread_only, because Alertmanager wrote to the root filesystemSolution
Add
read_only: trueto theprometheusservicesourcegraph/sourcegraph#18737 moves Alertmanager's files onto the
/prometheusdata volume.Do not merge this PR until the pinned
prometheusimage includes it.Test plan
Ran this branch with the image Buildkite built from sourcegraph/sourcegraph#18737:
prometheusstarts read-only, with no read-only or permission errorsobservability.alertsandobservability.silenceAlertsreach Alertmanager, and a webhook receives the notificationsmainwith the releasedprometheus:8.1.4690to this branch works on the same volumedocker compose stoptakes 0.5 seconds, so the default 10 second grace period is enoughprometheus:8.1.4690fails withopen /sg_config_prometheus/alertmanager.yml: read-only file systemLinked PRs
Merge in this order, because the two deploy PRs need a
prometheusimage with the fix:Amp threads