A container port is the port number on which an application in a container accepts connections. To send it a request, a client needs both an address and a port: for example, a pod IP address and port 8080. section 5.3.1
Listing 5.1 A basic pod manifest file
apiVersion: v1 #1
kind: Pod #2
metadata:
name: kiada #3
spec:
containers:
- name: kiada #4
image: luksa/kiada:0.1 #5
ports:
- containerPort: 8080 #6
This pod manifest records the application's port as `containerPort: 8080`, making the intended port visible to someone inspecting the pod. section 5.2.1
Declaring a container port is informative, not a requirement for connectivity. Leaving it out does not stop clients connecting to an application that accepts connections on the pod's IP address; declaring the wrong number does not change the port the application uses. Include it anyway so others can find the intended port. You can also name it for use by a Service. section 5.3.1
Keep these port numbers distinct:
- The application's port is where the container accepts connections. `kubectl get pod kiada -o wide` shows the pod IP; with the example application's port, a client able to reach that IP can request `10.244.2.4:8080`. section 5.3.1
- A Service's `port` is where the Service accepts connections; its `targetPort` identifies the port on a selected pod to which it forwards them. `targetPort` can use a number or a name declared in the container's port list. section 11.1.2
- For access from your computer when the pod IP is not reachable there, `kubectl port-forward kiada 8080` forwards a local port to the pod; you can then request `localhost:8080`. section 5.3.1
Listing 11.1 YAML manifest for the quote Service object
apiVersion: v1 #1
kind: Service #1
metadata:
name: quote #2
spec:
type: ClusterIP #3
selector: #4
app: quote #4
ports: #5
- name: http #5
port: 80 #5
targetPort: 80 #5
protocol: TCP #5
In this ClusterIP Service manifest, `port: 80` accepts Service connections and `targetPort: 80` forwards them to a matching pod. The equal numbers are separate settings. section 11.1.2
