Prevent Overlapping CronJobs with Concurrency Rule
Set concurrencyPolicy to Forbid so a slow cron job does not start a second instance while the first is still running.
Task
Configure kubectl patch cronjob nightly --type=merge -p '{"spec":{"concurrencyPolicy":"Forbid"}}' so the cluster enforces the policy at admission time instead of relying on manual review.
When to use this
A developer deploys a pod without kubectl patch cronjob nightly --type=merge -p '{"spec":{"concurrencyPolicy":"Forbid"}}' and it disrupts a node, causing evictions on a production cluster.
Prerequisites
- A Kubernetes cluster with kubectl access
- Cluster admin or namespace edit RBAC
Steps
1. Configure kubectl patch cronjob nightly --type=merge -p '{"spec":{"concurrencyPolicy":"Forbid"}}' in the project configuration file with the recommended defaults.
kubectl patch cronjob nightly --type=merge -p '{"spec":{"concurrencyPolicy":"Forbid"}}'
Expected output: The configuration is accepted and kubectl patch cronjob nightly --type=merge -p '{"spec":{"concurrencyPolicy":"Forbid"}}' runs without errors on the first invocation.
2. Run the check locally to verify kubectl patch cronjob nightly --type=merge -p '{"spec":{"concurrencyPolicy":"Forbid"}}' produces the expected result before pushing.
pnpm test
Expected output: Local run matches CI behavior; no surprises after push.
3. Add the gate to the CI pipeline so kubectl patch cronjob nightly --type=merge -p '{"spec":{"concurrencyPolicy":"Forbid"}}' blocks merge on failure.
- name: Run add cronjob concurrency rule
run: pnpm test
Expected output: Pull requests with failing kubectl patch cronjob nightly --type=merge -p '{"spec":{"concurrencyPolicy":"Forbid"}}' are blocked from merging.
Troubleshooting
Problem
The check passes locally but fails in CI
Solution
Pin dependency versions and the runtime to match CI exactly; reproduce with the same Docker image or act.
Problem
Configuration is rejected with a schema error
Solution
Check the tool version matches the config schema; older versions may not support newer fields.
Limitations
- The gate only runs on events that trigger the workflow; locally pushed commits bypass it.
- Configuration drift is possible if someone edits settings outside version control.
Enforce at admission
Start by measuring the problem. Set concurrencyPolicy to Forbid so a slow cron job does not start a second instance while the first is still running. The most common mistake is adding the gate without first confirming it catches the issue you care about. Run kubectl patch cronjob nightly –type=merge -p ‘{“spec”:{“concurrencyPolicy”:“Forbid”}}’ against the current codebase and inspect the output before wiring it into CI.
kubectl patch cronjob nightly --type=merge -p '{"spec":{"concurrencyPolicy":"Forbid"}}'Verify the policy
Once the gate is in place, make failures actionable. A failing kubectl patch cronjob nightly –type=merge -p ‘{“spec”:{“concurrencyPolicy”:“Forbid”}}’ should point to the exact file and line, not a generic error. Pin the tool version in the lockfile so a upstream release does not silently change behavior. Review the gate output in every pull request just like a test result.