Bite-Sized Kubernetes Part 5 - Services

Heave Ho!☸️

In Part 4 we learnt about deployments in kubernetes.
Moseying along now, to Services!🏴‍☠️

OBJECT	DESCRIPTION
Pods	The lowest level, single instance of an application
ReplicaSets	The next level, manages a set of pods
Deployments	The next level, manages a set of ReplicaSets
👉 Services	The next level, manages a set of deployments
Ingress	The next level, manages a set of services
Volumes	The next level, manages a set of ingress
Namespaces	The next level, manages a set of volumes
Cluster	The highest level, manages a set of namespaces

Services:

• K8s services enable the pods to communicate with the outside world.
• K8s services also enable the pods to communicate with each other.
• Services types:
  • NodePort service: a service that listens for requests on a port on the k8s node and forwards them to the pods
  • ClusterIP service: a service that creates a virtual IP address that is accessible only within the cluster, for communication between various services within the cluster.
  • Load Balancer service: a service that creates a load balancer in the cloud provider that forwards requests to the pods accordingly to balance load.

NodePort Service:

• Target port: the port on the pod that the service forwards requests to.
• Node port: the port on the k8s node that the service listens for requests on.
• Port: the port on the service that it listens on.
• The service has its own IP address, called the cluster IP address of the service.

• Creating a NodePort service:

  • Example service-definition.yml:
    

    apiVersion: v1
    kind: Service
    metadata:
      name: my-app-service
      labels:
        app: my-app
        type: my-type
    spec:
      type: NodePort
      ports:
        - targetPort: 8080
          port: 80
          nodePort: 30080
      # selector identifies the pods that the service will forward requests to
      selector:
        app: my-app
        type: my-type
    

  • The type property can be set to NodePort or ClusterIP or LoadBalancer depending on the type of service we're creating.

  • Once the .yml file is created, it can be used to create a service:
    

    $ kubectl create -f <file name>.yml
    

  • See list of services:
    

    $ kubectl get services
    

  • See detailed info about a service:
    

    $ kubectl describe service <service name>
    

  • To access the service from outside the cluster, use the node IP address and the node port:
    

    $ curl <node IP address>:<node port>
    

  • To access the service from inside the cluster, use the cluster IP address and the port:
    

    $ curl <cluster IP address>:<port>
    

• If there are multiple nodes in the cluster with their own pods, the service created can be accessed from all the nodes in the cluster.

ClusterIP Service:

• A service that creates a virtual IP address that is accessible only within the cluster, for communication between various services within the cluster.
• It groups together a set of pods and exposes them as a single service e.g. a service for all pods running the frontend app, a service for all pods running the backend app, for the database pods, redis pods etc.

• Creating a ClusterIP service:

  • Example service-definition.yml:
    

    apiVersion: v1
    kind: Service
    metadata:
      name: my-app-service
      labels:
        app: my-app
        type: my-type
    spec:
      type: ClusterIP
      ports:
          # target port: the port on the pod that the service forwards requests to
          # port: the port on the service that it listens on
          # no need to specify nodePort since this is a ClusterIP service
        - targetPort: 8080
          port: 80
      selector:
        app: my-app
        type: my-type
    

• Commands are same as the ones above for NodePort service.

LoadBalancer Service:

• A service that creates a load balancer in the cloud provider that forwards requests to the pods accordingly to balance load.

• Creating a LoadBalancer service:

  • Example service-definition.yml:
    

    apiVersion: v1
    kind: Service
    metadata:
      name: my-app-service
      labels:
        app: my-app
        type: my-type
    spec:
      type: LoadBalancer
      ports:
        - targetPort: 8080
          port: 80
      selector:
        app: my-app
        type: my-type
    

• Commands are same as the ones above for NodePort service.

You're doing great, Sailor! Captin Ahab would be proud!👨🏼‍✈️
Keep going! We'll look at "Ingress", "Volumes", "Namespaces" and revisit "Clusters" in the next and final part of this series!

Ahead Flank!!!🚀