I am working on a dev project that is written in rails but deployed within kubernetes. While doing local development, I am running the cluster using skaffold dev. This allows me to make changes locally and have it auto-sync to the running container without having to rebuild the image and push it anywhere. One issue with this approach is that in order to run database migrations locally, creating a deployment or job is a little bit heavy handed. Instead, we can simply connect to the running pod and run our db:migrate command there.

Connecting to a kubernetes pod

In order to run rails db:migrate we need to connect to a running pod. In order to determine which pod we need to connect to, we can use kubectl to get the name of the pod that is running the rails server. In my project, I have named that pod simply server-deployment.

> kubectl get pods
NAME                                   READY   STATUS    RESTARTS   AGE
server-deployment-6886cb479c-tt4mf   1/1     Running   36         73d

With the above, we can grab the full pod name and run the following command which will connect to the running pod, run the command, and exit.

kubectl exec server-deployment-6886cb479c-tt4mf -- /bin/bash -c "rails db:migrate"

However, we can do this in one single step instead of two. The single line command looks like this:

kubectl exec $(kubectl get pods | grep server | sed 's/ .*//') -- /bin/bash -c "rails db:migrate"

The command above is doing the following:

  • The sub-command $(kubectl ...) is getting all the pods, grepping for our server pod name, and then stripping everything but the first word that contains our full pod name
  • This is then substituted into the kubectl exec <our_pod_name>
  • Then finally, the /bin/bash -c "rails db:migrate" runs a one off command and auto-exits (we are not opening an interative connection
  • Profit!


To run rails db:migrate during our development flow, we can connect to the running rails pod and run that command via:

kubectl exec $(kubectl get pods | grep server | sed 's/ .*//') -- /bin/bash -c "rails db:migrate"