Kubectl command to list pods of a deployment in Kubernetes

Question

Is there a way to use kubectl to list only the pods belonging to a deployment? Currently, I do this to get pods:

kubectl get pods| grep hello

But it seems an overkill to get ALL the pods when I am interested to know only the pods for a given deployment. I use the output of this command to see the status of all pods, and then possibly exec into one of them.

I also tried kc get -o wide deployments hellodeployment , but it does not print the Pod names.

Answer 1

There's a label in the pod for the selector in the deployment. That's how a deployment manages its pods. For example for the label or selector app=http-svc you can do something like that this and avoid using grep and listing all the pods (this becomes useful as your number of pods becomes very large):

$ kubectl get pods -l=app=http-svc

or

$ kubectl get pods --selector=app=http-svc

Answer 2

K8s components are linked to each other by labels and selectors. There are just no built-in attributes of My-List-of-ReplicaSets or My-List-Of-Pods for a deployment. You can't get them from kubectl describe or kubectl get

As @Rico suggested above, you have to use label filters. But you can't simply use the labels that you specify in the deployment metafile because deployment will generate a random hash and use it as an additional label.

For example, I have a deployment and a standalone pod that share the same label app=http-svc . While the first two are managed by the deployment, the 3rd one is not and shouldn't be in the result.

ma.chi@~/k8s/deployments % kubectl get pods --show-labels
NAME                   READY   STATUS    RESTARTS   AGE   LABELS
http-9c89b5578-6cqbp   1/1     Running   0          7s    app=http-svc,pod-template-hash=574561134
http-9c89b5578-vwqbx   1/1     Running   0          7s    app=http-svc,pod-template-hash=574561134
nginx-standalone       1/1     Running   0          7s    app=http-svc
ma.chi@~/k8s/deployments %

The source file is

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: http-svc
  name: http
spec:
  replicas: 2
  selector:
    matchLabels:
      app: http-svc
  strategy: {}
  template:
    metadata:
      labels:
        app: http-svc
    spec:
      containers:
      - image: nginx:1.9.1
        name: nginx1

---

apiVersion: v1
kind: Pod
metadata:
  labels:
    app: http-svc
  name: nginx-standalone
spec:
  containers:
  - image: nginx:1.9.1
    name: nginx1-standalone

To exact spot the containers created and managed by your deployment, you can use the script below(which is ugly, but this is the best I can do)

DEPLOY_NAME=http
RS_NAME=`kubectl describe deployment $DEPLOY_NAME|grep "^NewReplicaSet"|awk '{print $2}'`; echo $RS_NAME

POD_HASH_LABEL=`kubectl get rs $RS_NAME -o jsonpath="{.metadata.labels.pod-template-hash}"` ; echo $POD_HASH_LABEL

POD_NAMES=`kubectl get pods -l pod-template-hash=$POD_HASH_LABEL --show-labels | tail -n +2 | awk '{print $1}'`; echo $POD_NAMES

Answer 3

Here's a tidier shell alias (based on this code by @kekaoyunfuwu) that only lists the pods of a deployment (no interim results are shown):

k_list_pods_in_deployment() {
  test $# -eq 0 && {
    echo "Missing deployment name" && kubectl get deployments
    return 1
  }
  local deployment="$1"; shift
  local replicaSet="$(kubectl describe deployment $deployment \
    | grep '^NewReplicaSet' \
    | awk '{print $2}'
  )"

  local podHashLabel="$(kubectl get rs $replicaSet \
    -o jsonpath='{.metadata.labels.pod-template-hash}'
  )"

  kubectl get pods -l pod-template-hash=$podHashLabel --show-labels \
    | tail -n +2 | awk '{print $1}'

}
alias k.list-pods-in-deployment=k_list_pods_in_deployment