Container output streams: kubectl logs options, stdout/stderr vs log files, /var/log/pods and /var/log/containers, sidecar log streaming

Kubernetes logging starts from one convention: containers should write logs to standard output (stdout) and standard error (stderr). The container runtime captures both streams and writes them to files on the node, and kubectl logs reads those files through the kubelet. Anything an application writes to a file inside its own container filesystem is invisible to kubectl logs.