K8s Hands-On: Multi-container pod and Service

#beginners #kubernetes #handson #tutorial

Introduction
Hi, I am Akshay Rao. This series will help you in hands on experience.
Pre-requisites
have done with create pod
https://dev.to/aksrao1998/k8s-hands-on-create-a-pod-8ef
Agenda
In the last blog we saw how to create a pod of single container but we were not able to access the nginx application. In this we will access the nginx and deploy multi-container pod.
Let's Start

we our pod named pod1 running but to access it we need to connect the container port 80 -> node port 80. So when the container port is connect to node port then the container is exposed to the outside world.
So to connect this ports we will use another k8s component that is service, in which using the labels we will tell the controller to connect.
we will do some slight changes in the pod1.yaml, before that if the pod is running pls delete it.

apiVersion: v1
kind: Pod
metadata:
  name:  pod1
  labels:         <- add this line to pod1.yaml
    type: webserver <- add this line to pod1.yaml
spec:
  containers:
  - name: nginx
    image: nginx:latest
    ports:
    - containerPort: 80

now create another file vi service.yaml and fill it with the below content

apiVersion: v1
kind: Service
metadata:
  name: basicservice #name of the service
spec:
  selector:
    type: webserver  <- same as in the pod1.yaml
  type: NodePort
  ports:
  - protocol: TCP
    port: 80

now deploy both of them

kubectl create -f pod1.yaml
kubectl create -f service.yaml

# verify
kubectl get po
[ts-akshay.rao@JP-FVFZ91DHL414 k8s-ckad (⎈|minikube:default)]$ k get svc
NAME           TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)        AGE
basicservice   NodePort    10.105.134.51   <none>        80:30933/TCP   106m
kubernetes     ClusterIP   10.96.0.1       <none>        443/TCP        19h

pick the ip address then ssh into the minikube as the cluster is running inside and curl the ip address.

[k8s-ckad (⎈|minikube:default)]$ minikube ssh
docker@minikube:~$ curl http://10.105.134.51:80
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

Multi-container Pod

edit the pod1.yaml (first delete the existing pod)and deploy it.

apiVersion: v1
kind: Pod
metadata:
  name:  pod1
  labels:
    type: webserver
spec:
  containers:
  - name: nginx
    image: nginx:latest
    ports:
    - containerPort: 80
  - name: collector
    image: fluentd

here we are using fluentd and nginx container in one pod.
now describe this pod

[k8s-ckad (⎈|minikube:default)]$ k describe pods pod1
Name:             pod1
Namespace:        default
Priority:         0
Service Account:  default
Node:             minikube/192.168.49.2
Start Time:       Tue, 03 Oct 2023 18:08:00 +0900
Labels:           type=webserver
Annotations:      <none>
Status:           Pending
IP:               
IPs:              <none>
Containers:
  nginx:
    Container ID:   
    Image:          nginx:latest
    Image ID:       
    Port:           80/TCP
    Host Port:      0/TCP
    State:          Waiting
      Reason:       ContainerCreating
    Ready:          False
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-hml2n (ro)
  collector:
    Container ID:   
    Image:          fluentd
    Image ID:       
    Port:           <none>
    Host Port:      <none>
    State:          Waiting
      Reason:       ContainerCreating
    Ready:          False
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-hml2n (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             False 
  ContainersReady   False 
  PodScheduled      True 
Volumes:
  kube-api-access-hml2n:
    Type:                    Projected (a volume that contains injected data from multiple sources)
    TokenExpirationSeconds:  3607
    ConfigMapName:           kube-root-ca.crt
    ConfigMapOptional:       <nil>
    DownwardAPI:             true
QoS Class:                   BestEffort
Node-Selectors:              <none>
Tolerations:                 node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
                             node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
  Type    Reason     Age   From               Message
  ----    ------     ----  ----               -------
  Normal  Scheduled  11s   default-scheduler  Successfully assigned default/pod1 to minikube
  Normal  Pulling    10s   kubelet            Pulling image "nginx:latest"
  Normal  Pulled     8s    kubelet            Successfully pulled image "nginx:latest" in 2.04728618s
  Normal  Created    8s    kubelet            Created container nginx
  Normal  Started    8s    kubelet            Started container nginx
  Normal  Pulling    8s    kubelet            Pulling image "fluentd

you can see the the events and of nginx and fluentd.

Links for further undertanding
https://kubernetes.io/docs/concepts/services-networking/service/#type-nodeport

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K8s Hands-On: Multi-container pod and Service

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