Abdullah Şamil Güser

Services

• We need to make the calls between pods dynamic
• A service is another type of K8s object
• Pod IPs are unreliable but service IPs are
• Durable (unlike pods)
  • Static IP address
  • Static DNS name
  • [servicename].[namespace].svc.cluster.local
• Services are ways to access pods
• Target pods using selectors

In kubernetes, we can use these services: ClusterIP (default), NodePort, LoadBalancer (L4), Ingress (L7)

ClusterIP

• ClusterIP is the default service
• Visibility
  • Cluster internal
• Port
  • The port the service is listening to
• TargetPort
  • Redirecting to the port the pod(5) are listening to
• Load balanced using round robin
  • Session affinity is configurable
• When to use
  • To provide a durable way to communicate with pods inside the

kubectl - ClusterIP Cheat Sheet (Applies to NodePort too)

# Create a service to expose a pod
kubectl expose po [podName] --port=80 --target-port=8080 --name=frontend

# Create a service to expose a deployment
kubectl expose deploy [deployName] --port=80 --target-port=8080

# Deploy the service
kubectl apply -f [definition.yaml]

# Get the services list
kubectl get svc

# Get extra info
kubectl get svc -o wide

# Describe the service
kubectl describe svc [serviceName]

# Delete the service
kubectl delete -f [definition.yaml]

# Delete the service using its name
kubectl delete svc [serviceName]

NodePort

• NodePort extend the ClusterIP service
• Visibility
  • Internal and external
• NodePort
  • The port the service is listening to externally
  • Statically defined, or dynamically taken from a range between 30000-32767
• Port
  • The port the service is listening to internally
• TargetPort
  • Redirecting to the port the pod(s) are listening to
• Must have public IP addresses
• Use any Node IP + nodePort to access the service

Load Balancing

• Layer 4 Load Balancing
  • Operating at the transport level (TCP)
  • Unable to make decisions based on content
  • Simple algorithms such as round-robin routing
• Layer 7 Load Balancing
  • Operates at the application level (HTTP, SMTP, etc)
  • Able to make decisions based on the actual content of each message
  • More intelligent load balancing decisions and content optimizations
    • Routing rules