How kubectl port-forward works?

Question

To start, it's useful to note and remember that in Kubernetes, every pod gets its own ip address from 10.*, that is usable only within the cluster. Now, the port-forward feature of kubectl simply tunnels the traffic from a specified port at your local host machine to the specified port on the specified pod. API server then becomes, in a sense, a temporary gateway between your local port and the Kubernetes cluster.

kubectl port-forward forwards connections to a local port to a port on a pod. Compared to kubectl proxy, kubectl port-forward is more generic as it can forward TCP traffic while kubectl proxy can only forward HTTP traffic.

kubectl port-forward is useful for testing/debugging purposes so you can access your service locally without exposing it.

Below is the name of the pod and it will forward it's port 6379 to localhost:6379.

kubectl port-forward redis-master-765d459796-258hz 6379:6379 

which is the same as

kubectl port-forward pods/redis-master-765d459796-258hz 6379:6379

or

kubectl port-forward deployment/redis-master 6379:6379 

or

kubectl port-forward rs/redis-master 6379:6379 

or

kubectl port-forward svc/redis-master 6379:6379

kubectl port-forward makes a specific Kubernetes API request. That means the system running it needs access to the API server, and any traffic will get tunneled over a single HTTP connection.

Having this is really useful for debugging (if one specific pod is acting up you can connect to it directly; in a microservice environment you can talk to a back-end service you wouldn't otherwise expose) but it's not an alternative to setting up service objects. When I've worked with kubectl port-forward it's been visibly slower than connecting to a pod via a service, and I've found seen the command just stop after a couple of minutes. Again these aren't big problems for debugging, but they're not what I'd want for a production system.

If you want to forward to a different port in localhost. Try this

kubectl port-forward <pod-name> <locahost-port>:<pod-port>

kubectl port-forward sample-pod-sadasds-sxawdd 8090:6379

The above command forwards to localhost 8090 from pod 6379

The port-forward command, Forwards one (or more) local ports to a pod.

This command is very useful for example in blue/green deployments where you would want to troubleshoot a misbehaving pod.

To take things even further, you could even execute some preliminary tests to the pods you feel could be more error-prone right inside your CI/CD pipeline in Jenkins by using multiple conditions, declarative pipeline.

Usage examples:

Listen on port 8888 locally, forwarding to 5000 in the pod

kubectl port-forward pod/mypod 8888:5000

Listen on port 8888 on all addresses, forwarding to 5000 in the pod

kubectl port-forward --address 0.0.0.0 pod/mypod 8888:5000

Listen on a random port locally, forwarding to 5000 in the pod

kubectl port-forward pod/mypod :5000

Listen on port 8888 on localhost and selected IP, forwarding to 5000 in the pod

kubectl port-forward --address localhost,10.19.21.23 pod/mypod 8888:5000

Listen on ports 5000 and 6000 locally, forwarding data to/from ports 5000 and 6000 in the pod

kubectl port-forward pod/mypod 5000 6000

Listen on ports 5000 and 6000 locally, forwarding data to/from ports 5000 and 6000 in a pod selected by the deployment

kubectl port-forward deployment/mydeployment 5000 6000

Listen on ports 5000 and 6000 locally, forwarding data to/from ports 5000 and 6000 in a pod selected by the service

kubectl port-forward service/myservice 5000 6000