Kubernetes: A very brief explanation of ports

A quick look at the various uses of "ports" in Kubernetes

Transcript

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

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2. 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
   

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3. 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
   

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4. 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
   

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5. 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
   

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6. 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
   

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7. 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
   

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8. 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
   

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