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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 counter-pod.yaml, which has a container which writes out some text to standard
output every second. (You can find different pod specifications here.)
{% highlight yaml %} {% raw %} 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'] {% endraw %} {% endhighlight %}
we can run the pod:
{% highlight console %} {% raw %} $ kubectl create -f ./counter-pod.yaml pods/counter {% endraw %} {% endhighlight %}
and then fetch the logs:
{% highlight console %} {% raw %} $ 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 ... {% endraw %} {% endhighlight %}
If a pod has more than one container then you need to specify which container's log files should be fetched e.g.
{% highlight console %} {% raw %} $ 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 ... {% endraw %} {% endhighlight %}
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.