Debug logs
Like all others program’s debugging, the most straightforward way for newbies and the easiest way for advanced developer is relying on logs. Same to debug kubelet, bumping up verbosity to show more logs is the most intuitive approach when facing an issue. Like most component in Kubernetes, kubelet uses klog for logging and there are 10 verbosity levels(0-9).
TL;DR: Bumping up to level 5 would satisfy most debugging needs.
| Level | Meaning | Example |
|---|---|---|
| 0 | Always on (Warning, Error, Fatal) | https://github.com/kubernetes/kubernetes/blob/d9c54f69d4bb7ae1bb655e1a2a50297d615025b5/pkg/kubelet/kubelet.go#L757-L757 |
| 1 | Default level logs when don’t want any verbosity | https://github.com/kubernetes/kubernetes/blob/d9c54f69d4bb7ae1bb655e1a2a50297d615025b5/pkg/kubelet/kubelet.go#L2527 |
| 2 | Most important logs when major operations happen, also the default verbosity level | https://github.com/kubernetes/kubernetes/blob/d9c54f69d4bb7ae1bb655e1a2a50297d615025b5/pkg/kubelet/kubelet.go#L483-L483 |
| 3 | Extended information | https://github.com/kubernetes/kubernetes/blob/d9c54f69d4bb7ae1bb655e1a2a50297d615025b5/pkg/kubelet/kubelet.go#L2176 |
| 4 | Debug level | https://github.com/kubernetes/kubernetes/blob/d9c54f69d4bb7ae1bb655e1a2a50297d615025b5/pkg/kubelet/kubelet.go#L1731 |
| 5 | Trace level | https://github.com/kubernetes/kubernetes/blob/d9c54f69d4bb7ae1bb655e1a2a50297d615025b5/pkg/kubelet/kubelet.go#L2821-L2821 |
| 6 | Display requested resources | https://github.com/kubernetes/kubernetes/blob/d9c54f69d4bb7ae1bb655e1a2a50297d615025b5/pkg/kubelet/cm/cgroup_manager_linux.go#L401 |
| 7 | Display HTTP request headers | https://github.com/kubernetes/kubernetes/blob/d9c54f69d4bb7ae1bb655e1a2a50297d615025b5/pkg/kubelet/logs/container_log_manager.go#L299 |
| 8 | Display HTTP request payload | https://github.com/kubernetes/kubernetes/blob/d9c54f69d4bb7ae1bb655e1a2a50297d615025b5/pkg/kubelet/prober/prober_manager.go#L192 |
By the time, this note was written. In kubelet related code, level 8 was only used in pkg/kubelet/prober/prober_manager.go and level 7 was only used in pkg/kubelet/logs/container_log_manager.go. And there are 11 occurrences that level 6 was used, and all of them are not part of workload lifecycle related.
Further readings
PREVIOUSLabs of CS350