Kubernetes labels cheatsheet

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Labels are key, value pairs that help identify a particular object (pods/deployment…)

Working with labels and pod

Create a pod with labels

 # Create pod
 kubectl run my-pod1 --image=nginx --labels="type=webserver,image-name=nginx"
 
 # Get all labels of a pod
  kubectl get pod my-pod1 --show-labels
  
  # Output
NAME      READY   STATUS    RESTARTS   AGE   LABELS
my-pod1   1/1     Running   0          44s   image-name=nginx,type=webserver

Add labels to running pods

# add a label
kubectl label pod my-pod1 opensource=true

#  add multiple labels
kubectl label pod my-pod1 a=1 b=2

# Get the labels
 kubectl get pod my-pod1 --show-labels
 
 # Output
NAME      READY   STATUS    RESTARTS   AGE     LABELS
my-pod1   1/1     Running   0          3m25s   a=1,b=2,image-name=nginx,opensource=true,type=webserve

Update an existing label

# Update current label (previously, a=1)
kubectl label pod my-pod1 a=2 --overwrite=true

# Get pod labels
kubectl get pod my-pod1 --show-labels

# Output
NAME      READY   STATUS    RESTARTS   AGE     LABELS
my-pod1   1/1     Running   0          4m56s   a=2,b=2,image-name=nginx,opensource=true,type=webserver

If you prefer, setting labels in YAML file is possible under metadata section.

Select a pod based on its label

Let’s create a few more pods with various labels

 kubectl run my-pod2 --image=nginx --labels="type=webserver,duty=backup,ver=1.0.0"

Now, we can use --selector to select pods:

kubectl get pods --selector="type=webserver"

# Output
NAME      READY   STATUS    RESTARTS   AGE
my-pod1   1/1     Running   0          9m49s
my-pod2   1/1     Running   0          33s

 kubectl get pods --selector="duty=backup"
 
 # Output, only my-pod2 is shown since only this pod has that label
NAME      READY   STATUS    RESTARTS   AGE
my-pod2   1/1     Running   0          87s

We can omit the value (after the = sign) to get the objects that have that label, regardless of the values

kubectl get pods --selector="a"

# Output
NAME      READY   STATUS    RESTARTS   AGE
my-pod1   1/1     Running   0          12m

kubectl get pods --selector="type"

#Output
NAME             READY   STATUS    RESTARTS   AGE
my-pod1          1/1     Running   0          13m
my-pod2          1/1     Running   0          4m17s
pod-with-label   1/1     Running   0          106m

Finally, we can select objects that have value exists in a possible set. First of all, get all pods and show their labels

# First get all pods and show their labels:
kubectl get pods --show-labels

# Output
NAME             READY   STATUS                       RESTARTS   AGE     LABELS
my-pod1          1/1     Running                      0          15m     a=2,b=2,image-name=nginx,opensource=true,type=webserver
my-pod2          1/1     Running                      0          6m43s   duty=backup,type=webserver,ver=1.0.0
my-pod3          1/1     Running                      0          9s      duty=backup,type=proxy,ver=1.0.0
nginx            1/1     Running                      0          33h     run=nginx
pod-with-label   1/1     Running                      0          108m    image=new-nginx,type=server
pod2             0/1     CreateContainerConfigError   0          5d15h   <none>
pod2-player      1/1     Running                      3          5d9h    <none>
pod3-player      1/1     Running                      3          5d8h    <none>
pvpod1           1/1     Running                      1          2d9h    <none>

As you can see, my-pod1, my-pod2, my-pod3 all have label type. If we want to select the ones with type webserver or server, we can run the following

kubectl get pods --selector="type in (webserver,server)"

# Output
NAME             READY   STATUS    RESTARTS   AGE
my-pod1          1/1     Running   0          18m
my-pod2          1/1     Running   0          9m11s
pod-with-label   1/1     Running   0          111m

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