Docker HEALTHCHECK is ignored by Kubernetes, causing silent traffic routing failures

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A technical analysis highlights a critical misconception: Docker's HEALTHCHECK directive, defined in a Dockerfile or docker-compose.yml, is completely ignored by Kubernetes when routing traffic to pods. While Docker Engine records health status internally and Docker Swarm acts on it, Kubernetes relies solely on its own livenessProbe, readinessProbe, and startupProbe definitions in the pod manifest. Without a readinessProbe configured, Kubernetes will send live traffic to a pod the moment its container starts, regardless of whether the application has finished initializing. This creates a false sense of security for developers migrating from Swarm or Compose environments, who may assume a defined HEALTHCHECK is sufficient. The article urges teams to treat Docker's HEALTHCHECK as a logging mechanism rather than a production availability feature when running workloads on Kubernetes.

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