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Kubernetes Services

Updated Apr 07, 2022 ·

Services​

A Service defines network access rules for Pods in a Kubernetes cluster. It selects Pods based on labels, allowing clients to reach these Pods via a fixed IP.

  • Use services to access groups of Pods by label
  • Clients connect through a fixed IP
  • The service distributes incoming requests across Pods

To view services in all namespaces:

kubectl get svc -A

When creating EKS clusters, two services are deployed by default:

  • kubernetes: allows communication with cluster nodes
  • kube-dns: connects to various Pods

Service Discovery​

Kubernetes uses two main methods for service discovery:

  • Environment Variables

    • Automatically injected by Kubernetes into containers
    • Uses a naming convention based on the service name

  • DNS

    • Creates DNS records for services automatically
    • Allows containers to discover services by querying cluster DNS

ClusterIP​

ClusterIP assigns an internal IP to a service, making it accessible only within the cluster. The kube-proxy component on each node routes requests to the service's endpoints.

  • Used for internal services, like databases or internal APIs
  • Provides a stable internal network identity for pods

Photo from Kubernetes Service Types Explained

NodePort​

NodePort exposes a service externally by opening a specific port on each node. Requests sent to this port route to the service’s cluster IP.

  • Limited external access, for testing or non-production apps
  • Accessible via <NodeIP>:<NodePort>

Loadbalancer​

A LoadBalancer service exposes the service to the internet using a cloud provider’s load balancer.

  • Automatically provisions a load balancer with a public IP
  • Configurable for SSL, health checks, and other features

Photo from Kubernetes NodePort vs LoadBalancer vs Ingress? When should I use what?

External Name​

ExternalName maps a service to an external DNS name instead of internal routing, useful for services outside the cluster.

  • Returns a CNAME record for the external DNS name
  • Often used for connecting to external databases or APIs

Kubernetes Ingress​

Ingress Controller manages layer 7 traffic, supporting SSL, load balancing, and path-based routing.

  • Routes external traffic based on domain and path
  • Supports SSL termination and custom routing rules

Once we have an ingress controller in place, we can leverage the ingress to define rules for inbound connections to services.