Using Stern to Tail Kubernetes Logs

If our service pod has a server and gateway container we'd be looking at something like this: ``` $ kubectl get pods # get pods to find pod ids $ kubectl describe pod service-1786497219-2rbt1 # get containers in pod $ kubectl log -f service-1786497219-2rbt1 server # pod 1 $ kubectl log -f service-1786497219-2rbt1 gateway # pod 1 $ kubectl log -f service-1786497219-8kfbp server # pod 2 $ kubectl log -f service-1786497219-8kfbp gateway # pod 2 $ kubectl log -f service-1786497219-lttxd server # pod 3 $ kubectl log -f service-1786497219-lttxd gateway # pod 3 ``` **Stern** To get around this we built [Stern](https://github.com/wercker/stern). It's a super simple utility that allows you to specify both the pod id and the container id as regular expressions. Any match will be followed and the output is multiplexed together, prefixed with the pod and container id, and color-coded for human consumption (colors are stripped if piping to a file). Here's how the service example would look: ``` $ stern service ``` This will match any pod containing the word service and listen to all containers within it. If you only want to see traffic to the server container you could do stern --container server service and it'll stream the logs of all the server containers from the 3 pods. The output would look something like this: ``` $ stern service + service-1786497219-2rbt1 › server + service-1786497219-2rbt1 › gateway + service-1786497219-8kfbp › server + service-1786497219-8kfbp › gateway + service-1786497219-lttxd › server + service-1786497219-lttxd › gateway + service-1786497219-8kfbp server Log message from server + service-1786497219-2rbt1 gateway Log message from gateway + service-1786497219-8kfbp gateway Log message from gateway + service-1786497219-lttxd gateway Log message from gateway + service-1786497219-lttxd server Log message from server + service-1786497219-2rbt1 server Log message from server ``` In addition, if a pod is killed and recreated during a deployment Stern will stop listening to the old pod and automatically hook into the new one. There's no more need to figure out what the id of that newly created pod is. **Configuration options** Stern was deliberately designed to be minimal so there's not much to it. However, there are still a couple configuration options we can highlight here. They're very similar to the ones built into kubectl so if you're familiar with that you should feel right at home. - timestamps adds the timestamp to each line - since shows log entries since a certain time (for instance --since 15min) - kube-config allows you to specify another Kubernetes config. Defaults to ~/.kube/config - namespace allows you to only limit the search to a certain namespaceRun stern --help for all options. **Examples**

This section provides examples of how to use Stern to tail logs from Kubernetes pods and containers, showcasing its ability to simplify log aggregation compared to `kubectl`. It demonstrates filtering by pod name and container name, and how Stern automatically reconnects to newly created pods during deployments. It also lists the available configuration options, such as adding timestamps, specifying a time since which to show logs, using a custom Kubernetes config file, and limiting the search to a specific namespace.