Diagnose: cron monitor shows missed check-ins

TL;DR

Run the job manually and watch the monitor's check-in history show the run with the right status and duration. Wrap the job so the start check-in fires first and the finish check-in fires in a finally block, with failure status set on exception. Then confirm the missed-job alert fires on a deliberately skipped run before calling it done.

When to use

You are seeing this: The monitor only knows what you tell it. Use this skill when you run into "Diagnose: cron monitor shows missed check-ins".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Step 1: is the check-in call reached?

The monitor only knows what you tell it. If the job crashes before the check-in call, or the call is after the work and the work hangs, the monitor correctly reports a miss. Wrap the job so the start check-in fires first and the finish check-in fires in a finally block, with failure status set on exception. A miss with no failure status usually means the process died before reporting.

Step 2: DSN authentication

Cron check-ins authenticate with the DSN, not the auth token (the CLI docs call this out: crons monitoring depends on DSN authentication). If the job's SENTRY_DSN is missing or points at the wrong project, check-ins go nowhere while the auth-token-based uploads keep working, which is confusing.

Step 3: schedule config vs reality

The monitor's expected schedule must match the actual cron schedule, including timezone. A job running at 02:00 UTC against a monitor expecting 02:00 America/Los_Angeles misses every day. Also check the grace period: a job that legitimately takes 25 minutes against a 15-minute expected duration with no grace period pages falsely.

Step 4: the job runner

If the scheduler itself is down (cron daemon, Celery beat, Cloud Scheduler), every monitor misses at once. One monitor missing is a job problem; all monitors missing is a scheduler problem.

Verify

Run the job manually and watch the monitor's check-in history show the run with the right status and duration. Then confirm the missed-job alert fires on a deliberately skipped run before calling it done.

Researched against live Sentry docs 2026-09-26. The cron monitoring page (docs.sentry.io/product/monitors-and-alerts/monitors/crons/) documents cron monitoring for scheduled recurring jobs with alerts and metrics for timeouts and failures, set up via CLI, HTTP, or supported SDKs. The CLI configuration page (docs.sentry.io/cli/configuration/) documents that some CLI functionality such as crons monitoring is dependent on DSN authentication (SENTRY_DSN / auth.dsn).