Logs

kubectl log is a command-line tool in Kubernetes used for retrieving logs from containers running inside pods within a Kubernetes cluster.

Example #

Single-container pod #

# log-simulator.yaml
apiVersion: v1
kind: Pod
metadata:
  name: log-simulator-pod
spec:
  containers:
  - image: mingrammer/flog
    name: log-simulator

k logs log-simulator-pod

Multi-container P0od #

# multi-container-log-simulator.yaml
apiVersion: v1
kind: Pod
metadata:
  name: mc-log-simulator-pod
spec:
  containers:
  - image: mingrammer/flog
    name: log-primary
  - image: mingrammer/flog
    name: log-secondary

k logs mc-log-simulator-pod log-secondary

Streaming Logs #

By default, kubectl log retrieves and displays the logs for a specific container from a given pod. You can also stream the logs in real-time by adding the -f or --follow flag. This is particularly useful for monitoring applications as they run.

kubectl logs -f <pod-name>

Timestamps #

To include timestamps in the log output, you can use the --timestamps flag. This helps you track when events occurred.

kubectl logs --timestamps <pod-name>

Previous Container State #

In cases where a container has terminated or encountered an issue, you can use kubectl log to retrieve logs from a previous instance of the container by adding the --previous flag.

kubectl logs --previous <pod-name>

Tail Logs #

To limit the number of lines displayed, you can use the -n or --tail flag to specify the number of lines to show from the end of the log.

kubectl logs --tail=<number-of-lines> <pod-name>

Output Format #

By default, kubectl log displays logs in plain text. However, you can specify other output formats such as JSON or YAML using the -o or --output flag.

kubectl logs -o json <pod-name>