Kubectl command to list pods of a deployment in Kubernetes - 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)
here are some examples command line:
# single label
kubectl get pods -l=app=http-svc
kubectl get pods --selector=app=http-svc
# multiple labels
kubectl get pods --selector key1=value1,key2=value2

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
}
deployment="$1"; shift
replicaSet="$(kubectl describe deployment $deployment \
| grep '^NewReplicaSet' \
| awk '{print $2}'
)"
podHashLabel="$(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