GKE list namespaces of another cluster

I need a list of all namespaces inside all the clusters in a GKE Project.

kubectl get ns will return namespaces in current-content and it's not ideal to keep switching contexts to get namespaces. Is there something in gcloud cli which I can use?

gcloud container clusters describe doesn't show namespaces :(

Solution

Interesting question.

Because there are 2-level of API interaction (Google Cloud, Kubernetes) and because each CLI (gcloud, kubectl) is configured distinctly, I think (!?) the only way to do this is by going through a KUBECONFIG configured with each cluster.

Repeatedly gcloud container cluster get-credentials is more expensive but should not be necessary. But context switching through KUBECONFIG is cheap and this should only entail updating the current-context value.

PROJECT="..."

Then to build the KUBECONFIG:

# Build KUBECONFIG comprising Project's clusters
# KUBECONFIG may include deleted Clusters
# Assumes that all the clusters are either REGION or ZONE
gcloud container clusters list \
--project=${PROJECT} \
--format="value(name,location)" |\
while read NAME LOCATION
do
  gcloud container clusters get-credentials ${NAME} \
  --region=${LOCATION} \
  --project=${PROJECT}
done

Then to iterate over it:

# Use the current Clusters in the Project as the source
# You could iterate over KUBECONFIG Clusters but this may not be current
gcloud container clusters list \
--project=${PROJECT} \
--format="value(name,location)" |\
while read NAME LOCATION
do
  kubectl config use-context gke_${PROJECT}_${LOCATION}_${NAME}
  kubectl get namespaces
done

Thinking about this again, there's an easier way. You don't need to revise the current context with --use-context, you can simply set the context on the kubectl get namespaces command:

gcloud container clusters list \
--project=${PROJECT} \
--format="value(name,location)" |\
while read NAME LOCATION
do
  kubectl get namespaces \
  --context=gke_${PROJECT}_${LOCATION}_${NAME}
done

Update

If your script has issues with | while read NAME LOCATION, please try the following alternative e.g. for the last example:

ROWS=$(\
  gcloud container clusters list \
  --project=${PROJECT} \
  --format="csv[no-heading](name,location)")

for ROW in ${ROWS}
do
  IFS=, read NAME LOCATION <<< ${ROW}
  kubectl get namespaces \
  --context=gke_${PROJECT}_${LOCATION}_${NAME}
done
```