Service Ports: port, targetPort and nodePort

Services and Networking / Guide 33 of 44 / Beginner

• Kubernetes1.36.4
• Cluster4 nodes
• Runtimecontainerd 2.2.6
• CNICalico v3.32.1
• TimeAbout 14 min

containerPort is informational. It does not open, publish or reserve anything - the process listens on whatever it listens on. Its only real functions are documentation and giving the port a NAME that targetPort can refer to.

This guide includes

Use this when a Service is configured and nothing answers. This matters because three numbers are involved and only two of them do anything - containerPort is informational, so a wrong one changes nothing while a wrong targetPort breaks everything.

• separating port, targetPort and containerPort by what each one actually controls
• declaring the wrong containerPort and confirming traffic still flows perfectly
• pointing targetPort at that same wrong number, and watching everything break
• naming the port instead, which is where containerPort finally earns its keep

Before you start

• A cluster and kubectl.
• The session creates namespace ckad-port, a Deployment whose containerPort is deliberately wrong, a Service in front of it, and a second pair using a named port.

1. 1

   Three numbers that are not the same thing

2. 2

   The wrong containerPort does not matter

3. 3

   The wrong targetPort breaks everything

4. 4

   Naming the port instead

Official sources

• Service
• Defining a Service
• Pod ports