Google Cloud Platform Kubernetes: A very brief explanation of ports Tim Hockin Senior Staff Software Engineer @thockin

Google Cloud Platform cluster pod.spec.ports[*].containerPort ● declares the existence of a port on a pod ● can be assigned a name or hostPort ● informational, not required node node node pod 3306 pod 8080 pod 8080 pod 80

Google Cloud Platform cluster pod.spec.ports[*].hostPort ● maps a specific port on a single node’s IP to a containerPort ● only one per-port per-node ● should be your LAST RESORT - if the pod moves, the ip:port changes node node node pod 3306 pod 8080 pod 8080 pod 80 80 80 80

Google Cloud Platform cluster service.spec.ports[*].port ● the virtual port on the service VIP ● service clients use this ● stable ip:port - does not change when pods move node node node pod 3306 pod 8080 pod 80 pod 8080 pod 8080 service 8080

Google Cloud Platform cluster service.spec.ports[*].targetPort ● maps a service port to backend containerPorts node node node pod 3306 pod 8080 pod 80 pod 8080 pod 8080 service 80

Google Cloud Platform cluster service.spec.ports[*].targetPort ● maps a service port to backend containerPorts ● can target a containerPort by number or name node node node pod mysql pod http pod http pod http pod http service 80

Google Cloud Platform service.spec.ports[*].nodePort ● maps a port on every node to a service port ● ports are allocated, random ● useful to interface with load-balancers that only understand nodes cluster node node node pod pod pod 31234 31234 3306 8080 8080 31234 pod 3306 pod 8080

Google Cloud Platform service.spec.ports[*].nodePort (OnlyLocal) ● annotation: service.beta.kubernetes.io/external-traffic=OnlyLocal ● changes how backends are chosen cluster node node node pod pod pod 31234 31234 3306 8080 8080 31234 pod 3306 pod 8080