Argo Cron Workflow Concurrency Quick Fix - Concurrency Policy

Q: What happens when a run is skipped due to concurrency policy?

With `Forbid`, skipped runs are recorded as "Skipped" status. The next scheduled interval creates a new workflow. No missed runs are retroactively executed. ||| What is the difference between Forbid and Replace? Forbid skips the new run if the previous is still running. Replace cancels the previous run and starts a new one, useful for refreshing caches or data. ||| Can I detect when a cron workflow was skipped? Yes, check the CronWorkflow status: `kubectl get cronwf -o yaml` shows `lastScheduleTime` and `lastSuccessfulTime`. Gaps indicate skipped runs.

DodaTech Updated 2026-06-26 1 min read

Argo CronWorkflow concurrency policy controls behavior when a scheduled run overlaps with a running instance. Wrong policy causes duplicate runs or skipped critical jobs. This guide covers the fix.

Quick Fix

Wrong

spec:
  schedule: "*/5 * * * *"
  concurrencyPolicy: "Allow"

With Allow, every 5-minute schedule creates a new workflow even if the previous one is still running. Long-running backups overlap and may corrupt data.

Right

spec:
  schedule: "*/5 * * * *"
  concurrencyPolicy: "Forbid"
  startingDeadlineSeconds: 120

# Expected output after applying the fix
# Workflow runs every 5 minutes
# If previous run exceeds 5 minutes, next run is skipped
# No overlapping executions
# Data consistency maintained

Prevention

Use Forbid for exclusive operations (backups, migrations)
Use Replace for stateless refresh operations
Use Allow only for idempotent, stateless workloads
Set startingDeadlineSeconds to skip stale pending runs
Monitor skipped runs via cron workflow status

DodaTech Tools

Doda Browser's concurrency monitor shows overlapping runs and skip events. DodaZIP archives concurrency decisions for capacity planning. Durga Antivirus Pro detects run overlap patterns that indicate performance issues.

FAQ

What happens when a run is skipped due to concurrency policy?

With Forbid, skipped runs are recorded as "Skipped" status. The next scheduled interval creates a new workflow. No missed runs are retroactively executed. ||| What is the difference between Forbid and Replace? Forbid skips the new run if the previous is still running. Replace cancels the previous run and starts a new one, useful for refreshing caches or data. ||| Can I detect when a cron workflow was skipped? Yes, check the CronWorkflow status: kubectl get cronwf <name> -o yaml shows lastScheduleTime and lastSuccessfulTime. Gaps indicate skipped runs.

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