Service IP

As explained in Road to Kubernetes

A cluster IP is the virtual IP address assigned to provide an internal network endpoint for a Kubernetes Service.

A service IP, or ClusterIP, is the internal virtual address assigned to a Kubernetes Service. Use it as the host value when connecting to that Service from within the cluster. section 8.4.3

Connect to a database Service

After entering a running Pod with kubectl exec and installing the psql client, run kubectl get service postgres-svc. Read the Cluster-IP value, such as 10.128.189.63, and use it to connect to the PostgreSQL Service from inside the cluster. section 8.4.3

Use a service IP with these practical limitations:

• Treat the address as internal; a ClusterIP-type Service does not accept traffic from outside the cluster. section 8.6
• Do not hard-code the address for durable configuration: Kubernetes provisions it dynamically, so its value is unpredictable. section 8.4.3
• Prefer the Kubernetes built-in DNS Service when predictable Service addressing is needed. section 8.4.3

Figure 8.13 kubectl get service output

Inspect the Cluster-IP value returned by kubectl get service. section 8.4.3

How Road to Kubernetes covers it

How deep it goes

Explains retrieval and in-cluster use, then flags address unpredictability without detailing forwarding internals.

Examples

Uses kubectl get service postgres-svc to obtain an address for an in-cluster psql connection.

What it assumes

Assumes a running Kubernetes cluster, a Service, and an in-cluster Pod with a client such as psql.

What you can do after

Apply it via kubectl and an in-cluster psql client to reach a database Service.

How it connects

Connects Kubernetes Services with Pods, container-to-container communication, and built-in DNS.

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Also explained in

• 

  liveBookmanning.com
  Kubernetes in Action, Second EditionA cluster IP is the virtual network address assigned to a Kubernetes Service for receiving and forwarding traffic to its endpoints.
• 

  liveBookmanning.com
  Kubernetes for DevelopersA cluster-local IP address is an address reachable within a Kubernetes cluster but not normally from the public internet.

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Related concepts

• Kubernetes DNS endpointalternative to · A Kubernetes DNS endpoint is a DNS name that identifies a Kubernetes Service or other resource within the cluster DNS domain.
• externalname service typecontrasts with · ExternalName is a Kubernetes Service type that aliases a service name to an external DNS name without allocating a cluster IP address.
• internal serviceproduced by · An internal service is a Kubernetes Service addressed through a private cluster IP for communication among workloads inside the cluster.
• Kubernetes APIproduced by · The Kubernetes API is the programmatic interface through which clients and components define, query, modify, and manage Kubernetes resources and cluster state.
• serviceused by · A Kubernetes Service is an API resource that provides stable network access and service discovery for a changing set of Pods or other specified destinations.
• loadbalancer serviceproduced by · A Kubernetes LoadBalancer Service is a Service type that exposes workloads externally through a provisioned or integrated network load balancer.

This explainer was generated by Manning's knowledge graph from the text of Road to Kubernetes. The section links point to the parts of the book it draws on.