k8s-cronjob-mcp

A read-only MCP server that lets an AI agent triage Kubernetes CronJobs: did it run, is it getting slower, has it quietly stopped succeeding, and why did that run fail?

General-purpose Kubernetes MCP servers expose CronJobs as just another resource type, so an agent has to fetch the CronJob, its Jobs, pods, Events and logs separately and then work out cron schedules, timezones and history limits itself. This server does that reasoning in tested code and returns a verdict with the evidence behind it, in one tool call, with zero write access to the cluster.

Where it fits

• Use it for: on-demand triage. "Which CronJobs in batch haven't succeeded this week, and why?" "Is the nightly report job running late?" "Why did last night's run fail?"

• It is not alerting. It only looks when an agent asks. Keep your existing alerts (for example Prometheus with kube-state-metrics' kube_cronjob_status_last_successful_time, or a dead-man's-switch service) to learn that something broke; use this server to find out what and why.

Tools

How the verdicts work

• Timezone. Schedules are evaluated in spec.timeZone when set, otherwise in UTC, which is what the kube-controller-manager almost always uses. The timezone of the machine running this server is never used. If your controller runs in another timezone, set CRON_DEFAULT_TIMEZONE.

• Schedule check. The expected last fire time is computed from spec.schedule. The actual last run comes from the batch.kubernetes.io/cronjob-scheduled-timestamp annotation on Jobs where available (Kubernetes 1.32+), falling back to status.lastScheduleTime. A run due less than 60s ago is still on-schedule; after that it is late until startingDeadlineSeconds, then missed. If startingDeadlineSeconds is unset, Kubernetes itself has no deadline; the server uses a 300s cutoff as a heuristic and says so in the verdict.

• Stopped firing. If no run has started for 3 or more scheduled fire times (and none is active), the CronJob is reported as stalled, even if it succeeded recently. This catches a frequent job that stopped an hour ago without waiting for the days window.

• Overrun. Compares the median duration of recent runs (and any active run) with the shortest gap between scheduled fire times. A CronJob whose runs use more than 80% of that gap is reported as at-risk (one slow run away from overrunning). A CronJob whose runs outlast that gap is reported as degraded/overrunning, with the effect of its concurrencyPolicy: with Forbid, scheduled runs are skipped or start late; with Allow, runs overlap; with Replace, runs are cancelled before they finish. Late starts (more than 60s after the scheduled time) are counted as supporting evidence.

• Silent failures. "Last success" is the later of status.lastSuccessfulTime (which survives Job deletion) and retained Jobs. The window is max(days, 2 × the schedule's cadence), so a weekly job is not flagged by a 7-day window. A brand-new CronJob that has not failed is not flagged. Suspended CronJobs are reported as suspended, not as failures.

• Failure cause. Checked in order: OOMKilled, DeadlineExceeded, image pull errors, container config errors, eviction, non-zero exit code (with hints such as 127 = command not found), unschedulable, then the most relevant warning Event. When a Job's pods are already gone, the cause falls back to what the Job object still records (failure reason and message, number of failed pods) and says why the evidence is missing, for example ttlSecondsAfterFinished.

• Every answer says what it is based on. Each result has asOf (when it was computed) and basis, one sentence such as "Failed Jobs that finished in the last 3 days, from only the Jobs Kubernetes still keeps" or "median of last 2 successful runs". When ALLOWED_NAMESPACES is set, scope shows those namespaces instead of "all namespaces".

Related MCP server: kops

Read-only by construction

This is deliberate and enforced in two independent places:

1. Code. The only Kubernetes calls are get/list/log reads. The ClusterReader interface in src/k8s/client.ts has no create/patch/delete/exec method for a tool to call.

2. RBAC. deploy/rbac.yaml grants get/list/watch on exactly cronjobs, jobs, pods, pods/log and events. Nothing else: no secrets, no pods/exec, no write verbs. npm run check:rbac asserts this against a real cluster (52 checks: reads allowed, every write denied).

Also worth knowing:

• Set ALLOWED_NAMESPACES=a,b to confine the server to specific namespaces; anything else is refused before any API call. This is enforced by the server, not by Kubernetes: the bundled RBAC is a ClusterRole, so the ServiceAccount itself can still read pods and logs cluster-wide. If you need Kubernetes to enforce the boundary, bind the same rules with a namespaced Role and RoleBinding in each namespace instead.

• Log tails are passed through a best-effort secret masker (passwords, tokens, API keys, bearer tokens). It is pattern-based and will not catch everything; treat logs as potentially sensitive.

• Job and pod data comes from live cluster state. There is no database. What you can see is bounded by successfulJobsHistoryLimit/failedJobsHistoryLimit, and Events expire after about an hour by default.

Install and use

Requires Node 20+. No install step is needed; npx fetches it on demand.

Add it to Claude Code (stdio):

claude mcp add k8s-cronjobs -e K8S_CONTEXT=my-context -- npx -y k8s-cronjob-mcp

Or to any MCP client config:

{
  "mcpServers": {
    "k8s-cronjobs": {
      "command": "npx",
      "args": ["-y", "k8s-cronjob-mcp"],
      "env": {
        "K8S_CONTEXT": "my-context",
        "ALLOWED_NAMESPACES": "batch,reports"
      }
    }
  }
}

To run from source instead: npm install && npm run build, then use node /absolute/path/to/dist/index.js as the command.

Docker (stdio, so run with -i and mount a kubeconfig read-only):

docker build -t k8s-cronjob-mcp .
docker run -i --rm -v ~/.kube/config:/home/node/.kube/config:ro k8s-cronjob-mcp

To give the server its own least-privilege identity, apply deploy/rbac.yaml and build a kubeconfig from the k8s-cronjob-mcp ServiceAccount (see scripts/sa-kubeconfig.sh for an example).

Get more out of it: raise history limits

By default Kubernetes keeps only the last 3 successful and 1 failed Job per CronJob. That is too little evidence for useful answers: duration trends need at least 4 successful runs, and consecutive failures cannot be counted past 1. For the CronJobs you care about, raise the limits:

spec:
  successfulJobsHistoryLimit: 10
  failedJobsHistoryLimit: 5

get_run_history warns when a CronJob's limits are too low.

Troubleshooting

Errors are short: what went wrong, the underlying error, what the server is using, and the fix. When a setting fixes it, the error names the variable, the value and the file to put it in. For example:

✗ No permission to read across all namespaces (403)
  Error: cronjobs.batch is forbidden: User "you@example.com" cannot list resource "cronjobs" ... at the cluster scope
  Using: context dev (pinned) · EKS dev-cluster (eu-west-2) · ~/.kube/config
  Fix:   Limit the server to namespaces you can read
         Check one: kubectl auth can-i list cronjobs -n <namespace>
  Set:   ALLOWED_NAMESPACES=team-a
         Claude Desktop: ~/Library/Application Support/Claude/claude_desktop_config.json → "env" of this server (then Cmd+Q and reopen)

To check everything step by step:

• From your agent: ask it to run check_setup. This is the most accurate check, because it runs with the same environment as your MCP client (which, for desktop apps, is not your shell's environment).

• From a terminal: npx -y k8s-cronjob-mcp --check (exit code 0 when everything passes).

If the configuration is broken at startup (for example a wrong K8S_CONTEXT), the server still starts and every tool returns the fix instead of failing silently. The startup summary and any problems are also written to the client's server log (Claude Desktop: ~/Library/Logs/Claude/mcp-server-k8s-cronjobs.log).

Try it on a local cluster

The demo uses kind and a repo-local kubeconfig (.kube/). The scripts never read your $KUBECONFIG and refuse to continue unless the context is a kind-* cluster, so no other cluster is touched.

npm run demo:up           # kind cluster + demo CronJobs + RBAC
npm run check:rbac        # prove the role is read-only
npm run test:integration  # runs every tool as the read-only ServiceAccount
npm run demo:down

The demo namespace contains: healthy, flaky (fails randomly), always-failing (the silent failure), paused (suspended), slowing (duration trend) and oom (OOMKilled). Give the CronJobs a few minutes (they fire every 2 minutes), then ask an agent: "Which CronJobs in demo are failing silently, and why?"

Development

npm test          # unit tests (no cluster needed)
npm run typecheck
npm run dev       # run from source over stdio

The logic lives in src/analysis/ as pure functions over Kubernetes objects, so it is tested with fixtures. src/tools/ is thin glue.

Publishing

See PUBLISHING.md for the npm release checklist.

Known limitations

• Only retained Jobs are visible, so consecutive-failure counts are capped by failedJobsHistoryLimit. A CronJob with a history limit of 0 leaves no evidence; the tools say so rather than reporting it as healthy.

• Trends need at least 4 successful runs (see raise history limits). The overrun check works from 1 finished run but is more reliable with more.

• list_recent_failures only sees failed Jobs Kubernetes still retains; failures removed by history limits or ttlSecondsAfterFinished are gone.

Roadmap

• A namespaced Role/RoleBinding option in deploy/.

• Optional Prometheus source for run history beyond the retained Jobs.

• compare_runs, an HTTP transport and a Helm chart.