kubectl exposes commands that can be used to create a Service for an application and assigns an IP address to access it from internet.
As far as I understand, to access any application within Kubernetes cluster there should be a Service resource created and that should have an IP address which is accessible from an external network.
But in case of port-forward how does kubectl create a connection to the application without an IP address which is accessible externally?
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 6379:6379or
kubectl port-forward deployment/redis-master 6379:6379 or
kubectl port-forward rs/redis-master 6379:6379 or
kubectl port-forward svc/redis-master 6379:6379Here is also some small port forwarding example to access a database service (clusterip) without exposing it.
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 8090:6379The above command forwards to localhost 8090 from pod 6379