Services

Network Model

The cluster (nodes and pods) is one big flat IP network:

• all nodes must be able to reach each other, without NAT
• all pods must be able to reach each other, without NAT
• pods and nodes must be able to reach each other, without NAT
• each pod is aware of its IP address (no NAT)

Service Types

Concept	Description	Diagram
ClusterIP	Service that creates virtual IP within the cluster to enable different services within the cluster to talk to each other the service is allocated an internal IP that other components can use to access the pods this IP address is reachable only from within the cluster (nodes and pods) when this service gets created, other applications within the cluster can access the service through service IP or service name Target ports allows to separate the port the service is available on from the port the application is listening on TargetPort = Port which the application is configured to listen on Port = is how the application will be accessed from the outside
NodePort	Service that exposes port on the Pod through a port on the node exposes the service on each Node’s IP via the defined static port no matter which Node within the cluster is accessed, the service will be reachable based on the port number defined Types of ports Port: port on the service itself (usually same as pod port) TargetPort: port on the Pod (where your app listens). This is an optional parameter, if not present, Port is taken NodePort: port on the node that is used to access web server externally (default in the 30000-32768 range) Code must be changed to connect to that new port number
LoadBalancer	An external load balancer is allocated for the service The load balancer is configured accordingly (e.g.: a NodePort service is created, and the load balancer sends traffic to that port)
ExternalName	The DNS entry managed by kube-dns will just be a CNAME to a provided record No port, no IP address, no nothing else is allocated