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Production health checks are not a choice between internal endpoints and external polling. They answer different questions: readiness tells an orchestrator whether an instance should receive traffic, liveness can tell it when to restart a stuck process, logs explain what went wrong, and an external monitor tests whether users can reach the service from outside. Use them together, with each signal tied to the action it is meant to trigger.
What each health signal is for
A health check is useful only when its result leads to the right response. In Kubernetes, probes have distinct operational effects; an external check and application logs provide other kinds of evidence.
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| Signal | Question it answers | Typical response | What it does not tell you |
|---|---|---|---|
| Readiness probe | Can this instance serve requests now? | Kubernetes marks the Pod not ready and excludes it from Service load balancing. | It does not mean the container should be restarted. A failed container can keep running while it recovers or waits for a dependency. Kubernetes documentation |
| Liveness probe | Is the process making enough progress to remain running? | A failed liveness probe can cause Kubernetes to restart the container. | It should not be used as a general test of every dependency. A transient downstream failure is not necessarily a dead process. Kubernetes documentation |
| Startup probe | Has this application completed its slow initialization? | When configured, Kubernetes waits for startup success before it begins liveness and readiness probes. | It is not a replacement for ongoing readiness or liveness checks after startup. Kubernetes documentation |
| Application logs and telemetry | What happened around a failure or slow response? | Operators correlate exceptions, dependency timeouts, deployments, and request behavior. | A log entry alone does not decide whether an instance should receive traffic or be restarted. |
| External synthetic check | Can a client reach the service through its public path? | An alert can flag externally visible failure or degraded response. | It generally cannot identify which replica is ready or explain an internal dependency failure. Microsoft’s Health Endpoint Monitoring pattern |
How to choose what an endpoint checks
Keep liveness narrow
A liveness endpoint should answer a process-health question: is the application unable to recover without a restart, for example because it is deadlocked? Avoid querying a database or other downstream service from liveness unless its failure truly means the process cannot make progress. If a shared dependency is slow or unavailable, turning that condition into a restart signal can make many otherwise-running instances restart together.
Kubernetes warns that “Incorrect implementation of liveness probes can lead to cascading failures.” The warning appears in its Configure Liveness, Readiness and Startup Probes documentation.
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Put serving requirements in readiness
Readiness is the traffic decision. Include a dependency check when that dependency is genuinely required for the instance to handle the requests it is expected to receive. If the dependency is temporarily unavailable, a readiness failure can keep the instance out of traffic without treating the application process as irrecoverable.
Do not make readiness an indiscriminate inventory of every service the application might ever call. A check should reflect whether this instance can serve its intended traffic; otherwise an optional or isolated dependency can unnecessarily remove capacity. Microsoft’s ASP.NET Core health-check guidance describes health checks and dependency checks in an application context.
Use startup allowance for slow initialization
When an application takes time to initialize, configure a startup probe so that liveness and readiness checks do not begin before startup succeeds. This avoids interpreting expected initialization time as an ongoing failure. Set the allowance to match the application’s actual startup behavior and deployment environment rather than copying a generic value.
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Tune probes to the workload
Kubernetes probe settings govern how often a check runs, how long it may take, and how many consecutive failures are tolerated. Its configuration documentation lists defaults of 10 seconds for periodSeconds, 1 second for timeoutSeconds, and 3 consecutive failures for failureThreshold. These are documented defaults, not recommended values for every application; the page was last modified October 16, 2025. Verify the fields and feature support for the Kubernetes release you deploy.
- Period: balance detection speed against the cost and frequency of checks.
- Timeout: keep the endpoint and any required dependency checks bounded so a health request cannot hang indefinitely.
- Failure threshold: allow for expected transient variation without delaying action so long that an unresponsive instance remains in service.
- Startup allowance: account for initialization time before ongoing probes take effect.
Keep health responses concise and suitable for machine consumption. Kubernetes recommends dedicated probe endpoints with minimal response bodies. Put detailed diagnostics in logs and telemetry rather than making verbose endpoint output an automation contract.
Why logs still matter
A probe can report failure, but it rarely explains the cause. Logs and telemetry let an operator connect the failure to an exception, dependency timeout, deployment change, or request pattern. The Microsoft monitoring pattern distinguishes endpoint-based health verification from logging and auditing; health checks do not replace those records.
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Probe traffic can also produce connection-reset or broken-pipe log entries. Kubernetes calls out this effect in its probe guidance. Identify probe requests consistently in the application and interpret these entries in context; a particular filtering method depends on the framework and logging stack.
What external polling can and cannot establish
An external monitor checks the service from outside its process or host environment. A synthetic check can request a public URL and evaluate a response code, latency, or a small expected response fragment. Because it follows a different path, it can reveal problems with reachability, routing, DNS, TLS, or an edge layer that an in-process check cannot see.
That outside view is not an instance-level traffic decision. A successful request does not establish that every replica is ready, and a failed request does not by itself identify whether the cause is an application, network path, or dependency. Combine external checks with orchestrator probes and diagnostic evidence rather than treating a single vantage point as complete coverage. Microsoft’s Health Endpoint Monitoring pattern describes endpoint monitoring as one part of an operational monitoring approach.
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Use Kubernetes API health paths for the API server
Kubernetes API server health endpoints are separate from application-defined probe paths. For API server checks, use /livez and /readyz; the older /healthz endpoint is deprecated. A 200 response indicates the status represented by the endpoint. The API reference distinguishes readiness, which concerns accepting traffic, from liveness, which concerns whether a restart is appropriate. Verbose output for individual checks is intended for human operators, not as a machine-facing contract. Kubernetes API health endpoints
Plan shutdown and recovery behavior
During shutdown, an application should stop advertising readiness before it exits so traffic can drain in line with the deployment platform’s behavior. The precise sequence and drain guarantees depend on the orchestrator, load balancer, and application configuration; do not assume one platform’s timing applies universally. Keep the endpoint state aligned with what the instance can actually serve, and verify the complete shutdown path in the environment where it runs.
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Quick Recap
A practical design checklist
- Give readiness, liveness, and startup checks distinct meanings, using separate paths or clearly differentiated probe services where supported.
- Make readiness reflect whether the instance can handle its intended requests; include only dependencies whose availability is necessary for that work.
- Make liveness narrow enough that a recoverable dependency outage does not trigger a restart.
- Bound dependency checks with timeouts and keep probe responses short.
- Tune check frequency, timeout, failure tolerance, and startup allowance for the application and its recovery characteristics.
- Use logs and telemetry to diagnose failures; treat probe-generated connection errors in context.
- Add an external synthetic check for the user-visible path, then alert and investigate with the internal signals that can identify instance state and operational causes.
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