Bite-Sized Kubernetes Part 5 - Services

#kubernetes #devops #containers

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!!!🚀