10. K8 Services

Service

• Each pod has its own IP address

  • Pods are ephemeral - destoryed frequently

• Service gives stable IP address

• Provides load balancing

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Types

1. ClusterIP

• default type

• pod gets ip address from node's range

How Service Knows which Pod to Forward Request to

How Service Knows which Port to Forward Request to

Service Endpoints

• K8 create endpoints object

• have same name as service

• keeps track of which pods are members/endpoint of the service

Multiple Ports Service

2. Headless Service

• clients want to communicate with 1 specific pod directly

• pod wants to talk directly with specific pod not a randomly selected pod

• Use Case: Stateful applications like databases

  • pod replicas are not identical

• Client needs to figure out IP address of each pod

  • Option 1 - API call to K8 API Server (X)

  • Option 2 - DNS Lookup (Recommended)

    • DNS lookup for service - returns single ip address

    • If ClusterIP is set to None - returns pod ip address instead

    • 

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Service Type Attributes

1. ClusterIP

   • Only accessible within cluster

2. NodePort

   • extension of clusterip service

   • External traffic has access to fixed port on each worker node

   • 
   • 
   • not secure and efficient since port is directly accessible externally

   • not used in production environments

3. Load Balancer

   • extension of nodeport service

   • becomes accessible externally through cloud provider loadbalancers

   • 
   • secure and efficient since port is not accessible directly but via load balancer

   • used in production environments

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