[Kubernetes] Service & Service Types

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Service & Service Types

• Service: a stable address for pods(i.e an endpoint that is consistent so that other things(in and outside the cluster) can access it)
  • pods don’t have a DNS name automatically when created, needs to create a service on top of them
  • CoreDNS resolve services by name
• There are different types of services
  • ClusterIP
  • NodePort
  • LoadBalancer
  • ExternalName
• Kubernetes Ingress: Specifically designed for HTTP traffic (inbound to the cluster)

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Service Types

ClusterIP

• default
• Single, internal virtual IP allocated
• only reachable from within cluster(nodes & pods, i.e. one set of pods connecting to other set of pods)
• pods can reach service via apps port number
• always avaiable in k8s

NodePort

• allows connection outside the cluster through the IP address of the nodes
• high port allocated on each node
• port is open on every node’s IP
• Anyone can connect (if they can reach the node)
• Other pods need to be updated to this port
• always avaiable in k8s

LoadBalancer

• controls a LB endpoint external to the cluster
• only available when infra porvider give a LB(e.g. AWS ELB, etc)
  • mostly used in the cloud
• created NodePort + ClusterIP services, tells LB to send to NodePort

ExternalName

• used less often
• not about inbound, rather for outbound
• adds CNAME DNS record to CoreDNS only
• Not used for Pods, but for giving pods as DNS name to use for something outside k8s

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ref

• 🔗 service