How kubectl port-forward works?

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

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

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

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.