Hi there,

It’s spring cleaning time and your K8s deployment might have accumulated some dirt since the last time you scrubbed it. If that's the case, here's how to manage this with labels.

Labels communicate precious bits of information about the ownership of a node, a pod, or other objects - all for faster tracking and operational decision-making.

But many engineers don't know how to use them efficiently.

Without further ado, here are 3 ways you can fine-tune your labeling strategy for 2023 and improve your team’s efficiency.

If labels are a totally new topic for you, check this guide first.

1. Group resources for object queries

If you add the same label key-value pair to multiple resources, other people can easily query for all of them. 

Suppose you discover that a development environment is unavailable. At this point, you can quickly check the status of all pods, including the label environment:dev.

Here’s an example command:

> kubectl get pods -l 'environment=dev'

NAME    READY   STATUS              RESTARTS    AGE

nginx   0/1     CrashLoopBackOff    1           5m

This lets you instantly see the affected pods and resolve the issue much faster.

The alternative? Going through all the resources and picking just the ones in the dev environment.

In a complex scenario with many deployments, finding the right dev pods would take you ages if the team didn’t add the environment:dev label to the resources. You’d have to use a generic kubectl get pods command and then comb through the output using a tool like grep.

2. Perform bulk operations

Imagine that poor engineer who has to remove all staging environments every night to reduce costs. 

You can automate this task using labels.

Here’s a command that deletes all objects labeled environment:local, environment:dev or environment:staging:

> kubectl delete deployment,services,statefulsets -l 'environment in (local,dev,staging)'

3. Schedule pods based on node labels

K8s uses labels a lot for scheduling pods to the right nodes. Smart labeling gives more control over the resources you create by making K8s schedule specific
deployments on specific nodes.

Here’s how this works in practice:

> kubectl get nodes

NAME             STATUS ROLES AGE VERSION

gke-node-1fe68171 Ready <none> 1d v1.22.12-gke.2300

gke-node-3cdf3d2b Ready <none> 3d v1.22.12-gke.2300

gke-node-5f7b4cf1 Ready <none> 5d v1.22.12-gke.500


> kubectl get nodes -l ‘critical=true’

No resources found

At this point, there are no nodes with the label critical:true. 

Let’s create a pod that has to be scheduled on a node with the label critical:true using a node selector. Here is a pod.yaml configuration file for that:

apiVersion: v1
kind: Pod
metadata:
 name: nginx
 labels:
   environment: prod
spec:
 nodeSelector:
   critical: "true"
 containers:
   - image: nginx
     name: nginx
     resources:
       requests:
         cpu: 500m

This is what happens when you apply that:

> kubectl apply -f pod.yaml
pod/nginx created


> kubectl get pod nginx

NAME  READY STATUS  RESTARTS AGE
nginx 0/1   Pending 0        1m


> kubectl get events --field-selector involvedObject.name=nginx

LAST SEEN TYPE REASON OBJECT MESSAGE

46s   Warning FailedScheduling pod/nginx 0/1 nodes are available: 1 node(s) didn't match Pod's node affinity/selector. preemption: 0/1 nodes are available: 1 Preemption is not helpful for scheduling.

The pod can’t get scheduled on any of the nodes since none of them has the required label. So, let’s label a node with the required label:

> kubectl label node gke-node-5f7b4cf1 critical=true

node/gke-node-5f7b4cf1 labeled

> kubectl get nodes -l 'critical=true'

NAME              STATUS ROLES  AGE VERSION
gke-node-5f7b4cf1 Ready  <none> 5h  v1.22.12-gke.500

And now, let’s check the pod:

> kubectl get pod nginx

NAME  READY STATUS  RESTARTS AGE

nginx 1/1   Running 0        3m31s

The pod was successfully scheduled to the node!

If we specified multiple labels in the node selector, they must all be satisfied by a node for the pod to get scheduled on it.

I hope this helps you clean up your K8s deployments and labeling strategy!

Cheers,

Allen