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WARNING WARNING WARNING

PLEASE NOTE: This document applies to the HEAD of the source tree only. If you are using a released version of Kubernetes, you almost certainly want the docs that go with that version.

Documentation for specific releases can be found at releases.k8s.io.

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Logging

Logging by Kubernetes Components

Kubernetes components, such as kubelet and apiserver, use the glog logging library. Developer conventions for logging severity are described in docs/devel/logging.md.

Examining the logs of running containers

The logs of a running container may be fetched using the command kubectl logs. For example, given this pod specification which has a container which writes out some text to standard output every second counter-pod.yaml:

 apiVersion: v1
 kind: Pod
 metadata:
   name: counter
 spec:
   containers:
   - name: count
     image: ubuntu:14.04
     args: [bash, -c, 
            'for ((i = 0; ; i++)); do echo "$i: $(date)"; sleep 1; done']

we can run the pod:

 $ kubectl create -f counter-pod.yaml
 pods/counter

and then fetch the logs:

$ kubectl logs counter
0: Tue Jun  2 21:37:31 UTC 2015
1: Tue Jun  2 21:37:32 UTC 2015
2: Tue Jun  2 21:37:33 UTC 2015
3: Tue Jun  2 21:37:34 UTC 2015
4: Tue Jun  2 21:37:35 UTC 2015
5: Tue Jun  2 21:37:36 UTC 2015
...

If a pod has more than one container then you need to specify which container's log files should be fetched e.g.

$ kubectl logs kube-dns-v3-7r1l9 etcd
2015/06/23 00:43:10 etcdserver: start to snapshot (applied: 30003, lastsnap: 20002)
2015/06/23 00:43:10 etcdserver: compacted log at index 30003
2015/06/23 00:43:10 etcdserver: saved snapshot at index 30003
2015/06/23 02:05:42 etcdserver: start to snapshot (applied: 40004, lastsnap: 30003)
2015/06/23 02:05:42 etcdserver: compacted log at index 40004
2015/06/23 02:05:42 etcdserver: saved snapshot at index 40004
2015/06/23 03:28:31 etcdserver: start to snapshot (applied: 50005, lastsnap: 40004)
2015/06/23 03:28:31 etcdserver: compacted log at index 50005
2015/06/23 03:28:31 etcdserver: saved snapshot at index 50005
2015/06/23 03:28:56 filePurge: successfully removed file default.etcd/member/wal/0000000000000000-0000000000000000.wal
2015/06/23 04:51:03 etcdserver: start to snapshot (applied: 60006, lastsnap: 50005)
2015/06/23 04:51:03 etcdserver: compacted log at index 60006
2015/06/23 04:51:03 etcdserver: saved snapshot at index 60006
...

Cluster level logging to Google Cloud Logging

The getting started guide Cluster Level Logging to Google Cloud Logging explains how container logs are ingested into Google Cloud Logging and shows how to query the ingested logs.

Cluster level logging with Elasticsearch and Kibana

The getting started guide Cluster Level Logging with Elasticsearch and Kibana describes how to ingest cluster level logs into Elasticsearch and view them using Kibana.

Ingesting Application Log Files

Cluster level logging only collects the standard output and standard error output of the applications running in containers. The guide Collecting log files within containers with Fluentd explains how the log files of applications can also be ingested into Google Cloud logging.

Known issues

Kubernetes does log rotation for kubernetes components and docker containers. The command kubectl logs currently only read the latest logs, not all historical ones.

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