Accessing logs from the CLI


  • The kubectl logs commands has limitations:

    • it cannot stream logs from multiple pods at a time

    • when showing logs from multiple pods, it mixes them all together

  • We are going to see how to do it better

Doing it manually

  • We could (if we were so inclined), write a program or script that would:

    • take a selector as an argument

    • enumerate all pods matching that selector (with kubectl get -l ...)

    • fork one kubectl logs --follow ... command per container

    • annotate the logs (the output of each kubectl logs ... process) with their origin

    • preserve ordering by using kubectl logs --timestamps ... and merge the output

  • We could do it, but thankfully, others did it for us already!


Stern is an open source project by Wercker.

From the README:

Stern allows you to tail multiple pods on Kubernetes and multiple containers within the pod. Each result is color coded for quicker debugging.

The query is a regular expression so the pod name can easily be filtered and you don't need to specify the exact id (for instance omitting the deployment id). If a pod is deleted it gets removed from tail and if a new pod is added it automatically gets tailed.

Exactly what we need!

Installing Stern

  • Run stern (without arguments) to check if it's installed:

    $ stern
    Tail multiple pods and containers from Kubernetes
      stern pod-query [flags]
  • If it is not installed, the easiest method is to download a binary release

  • The following commands will install Stern on a Linux Intel 64 bit machine:

    sudo curl -L -o /usr/local/bin/stern \
    sudo chmod +x /usr/local/bin/stern

Using Stern

  • There are two ways to specify the pods for which we want to see the logs:

    • -l followed by a selector expression (like with many kubectl commands)

    • with a "pod query", i.e. a regex used to match pod names

  • These two ways can be combined if necessary


  • View the logs for all the rng containers:
    stern rng

Stern convenient options

  • The --tail N flag shows the last N lines for each container

    (Instead of showing the logs since the creation of the container)

  • The -t / --timestamps flag shows timestamps

  • The --all-namespaces flag is self-explanatory


  • View what's up with the weave system containers:
    stern --tail 1 --timestamps --all-namespaces weave

Using Stern with a selector

  • When specifying a selector, we can omit the value for a label

  • This will match all objects having that label (regardless of the value)

  • Everything created with kubectl run has a label run

  • We can use that property to view the logs of all the pods created with kubectl run

  • Similarly, everything created with kubectl create deployment has a label app


  • View the logs for all the things started with kubectl create deployment:
    stern -l app