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An exec liveness probe runs a command inside a container. Kubernetes considers it successful only when that command exits with status 0. If the executable is missing or cannot be launched, the probe fails; once failures reach the configured threshold, Kubernetes treats the container as unhealthy and restarts it. A missing binary can therefore create a recurring restart loop—not because the application necessarily failed, but because its health check cannot run.
How a missing executable leads to restarts
An exec probe runs the configured command in the container. It does not automatically start a shell: the command must specify one if shell behavior is needed. The executable must exist in the final image, be usable with its permissions, and be discoverable at the configured path or through the execution environment’s PATH. Kubernetes documents the command and success contract in its liveness, readiness, and startup probes guide.
A runtime error such as executable file not found in $PATH has appeared in a Kubernetes issue report, but that wording is an illustrative diagnostic, not a guaranteed message for every missing-command failure: Kubernetes issue report.
Repeated failures matter for liveness because, as Kubernetes puts it, “Liveness probes determine when to restart a container.” The failure threshold is the number of consecutive failed checks required before Kubernetes takes action. Raising that threshold can delay a restart, but it cannot make an absent executable available.
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First, confirm whether the failure is liveness or readiness
These probes answer different operational questions. A failed liveness probe can trigger a container restart; a failed readiness probe leaves the container running but marks it unready, so it is removed from Service traffic. Kubernetes explains the distinction in its probe documentation and Pod and endpoint termination tutorial.
| Probe | What failure means | Typical consequence |
|---|---|---|
| Liveness | The container is considered unhealthy. | Kubernetes restarts the container after the configured failure threshold. |
| Readiness | The container should not receive traffic now. | The container remains running but is marked unready and excluded from Service traffic. |
If the real concern is whether the application should receive traffic, readiness is the relevant signal. Do not use liveness for a temporary condition that a restart is unlikely to fix. Kubernetes warns that “Incorrect implementation of liveness probes can lead to cascading failures” in its probe configuration guidance.
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Diagnose the probe in the running container
- Read the manifest command exactly. Inspect the affected container’s
livenessProbe.exec.command. Kubernetes does not implicitly invoke a shell, so commands relying on shell operators, expansions, or built-ins must explicitly run an appropriate shell. - Check the final image, not just the build environment. Verify that the executable is included in the image actually deployed, has suitable execute permissions, and is reachable through the path or
PATHused by the probe. A utility available in a builder or development image may be absent from a minimal runtime image. - Inspect Pod events and container state. Look for
Unhealthyevents, liveness probe failures, runtime errors, and changes to the container restart count. Kubernetes’ tutorial demonstrates checking Pod events when diagnosing probe behavior. - Ask whether restarting can fix the tested condition. A liveness check should detect a condition for which restarting the container is a plausible recovery. A temporary downstream dependency problem or load spike is usually a poor liveness condition unless restarting is deliberately the recovery action.
- Choose a probe mechanism that matches the check. If the health signal can be tested over HTTP, TCP, or gRPC, those probe mechanisms may avoid depending on a utility binary in the image. Use exec when running a command inside the container is the appropriate check.
Check timing and initialization settings
The current Kubernetes probe documentation lists these defaults: failureThreshold is 3 consecutive failures, periodSeconds is 10 seconds, and timeoutSeconds is 1 second. The documented minimum is 1 for failureThreshold and timeoutSeconds. Liveness failures at the threshold cause a restart; readiness failures mark the container unready. These are documented defaults, not a guarantee that a particular manifest uses them. See the Kubernetes probe configuration reference.
If the application needs time to initialize, a startup probe can prevent liveness and readiness checks from running too early. Kubernetes describes startup probes as a way to protect slow-starting containers while they initialize in its configuration guide. A startup probe addresses initialization timing; it does not correct a missing executable in an exec command.
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Choose a probe without adding a new failure mode
Match the mechanism to the health condition and its operational consequence. An exec check is useful when a command can accurately test local application health, but it depends on that executable being present and launchable. HTTP, TCP, and gRPC checks are alternatives when they can test the intended condition directly. Liveness determines restart behavior; readiness determines traffic eligibility.
Exec probes also create processes. Kubernetes cautions that frequent exec probes in clusters with many Pods may add CPU overhead. Account for probe frequency and Pod density when deciding whether a process-based check is appropriate; do not trade away a meaningful health check without considering what the replacement measures.
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