> For the complete documentation index, see [llms.txt](https://bagus-cahyono.gitbook.io/programming-notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://bagus-cahyono.gitbook.io/programming-notes/cka/03_pod.md).

# Pod

Pods are the smallest deployable units of computing that you can create and manage in Kubernetes.

A Pod is a group of one or more containers, with shared storage and network resources, and a specification for how to run the containers.

Think of a Pod as a wrapper around containers, ensuring they work as a single unit.

## Single Container Pod

We can start or run a particular image in a pod using `kubectl run` command.

```bash
➜ kubectl run nginx --image=nginx --port=80
pod/nginx created
```

This command will create a pod named `nginx` will single container named `nginx` using image `nginx` and open port `80`. We can see the details using command `kubectl describe`.

```bash
➜ kubectl describe pod nginx 
Name:             nginx
Namespace:        default
Priority:         0
Service Account:  default
Node:             minikube/192.168.49.2
Start Time:       Tue, 04 Feb 2025 12:48:15 +0700
Labels:           run=nginx
Annotations:      <none>
Status:           Running
IP:               10.244.0.94
IPs:
  IP:  10.244.0.94
Containers:
  nginx:
    Container ID:   docker://6f804d723c05e62267a7b70896ec07dac53991f4e152874a8e713144c57c02d2
    Image:          nginx
    Image ID:       docker-pullable://nginx@sha256:0a399eb16751829e1af26fea27b20c3ec28d7ab1fb72182879dcae1cca21206a
    Port:           80/TCP
    Host Port:      0/TCP
    State:          Running
      Started:      Tue, 04 Feb 2025 12:48:19 +0700
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-6bc8f (ro)
...
```

We can also use `yaml` file to define pod configuration. The command `kubectl run` we previously use is more or less equal with this configuration below.

```yaml
apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
  - name: nginx
    image: nginx
    ports:
    - containerPort: 80
```

Explanation:

* `metadata.name: nginx`: The name of the Pod (must be unique in the namespace).
* `spec`: The specification of the Pod.
* `containers`: List of containers that will run inside this Pod.
* `- name: nginx`: The name of the container inside the Pod.
* `image: nginx`: The Docker image used to run the container (pulled from Docker Hub by default).
* `ports`: Defines which ports are opened on the container.
* `containerPort: 80`: The container listens on port 80.

To apply it as usual we can use `kubectl apply -f <file>` command.

## Multiple Container Pod

To create a pod that have multiple containers we just need to add new entries in `containers` section. Create new file `pod.yaml` and put example configuration below.

```yaml
apiVersion: v1
kind: Pod
metadata:
  name: nginx-with-logger
spec:
  containers:
  - name: nginx
    image: nginx
    ports:
    - containerPort: 80
  - name: logger
    image: busybox
    command: ["sh", "-c", "while true; do echo 'Logging...'; sleep 10; done"]
```

Apply the configuration file using `kubectl apply` and let see the details using `kubectl describe` command.

```bash
➜ kubectl apply -f pod.yaml 
pod/nginx-with-logger created
```

```bash
➜ kubectl describe pod nginx-with-logger 
Name:             nginx-with-logger
Namespace:        default
Priority:         0
Service Account:  default
Node:             minikube/192.168.49.2
Start Time:       Tue, 04 Feb 2025 13:49:17 +0700
Labels:           <none>
Annotations:      <none>
Status:           Running
IP:               10.244.0.95
IPs:
  IP:  10.244.0.95
Containers:
  nginx:
    Container ID:   docker://7ff16ce361c2acba92bc4e7a5ad4591c2f8943dc9fc766d8c89870a66e35d012
    Image:          nginx
    Image ID:       docker-pullable://nginx@sha256:0a399eb16751829e1af26fea27b20c3ec28d7ab1fb72182879dcae1cca21206a
    Port:           80/TCP
    Host Port:      0/TCP
    State:          Running
      Started:      Tue, 04 Feb 2025 13:49:21 +0700
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-dmx2c (ro)
  logger:
    Container ID:  docker://a2bf248b0f9cad05d9e9af0e99fc273e479bda47018c43b406d3469ed93a88e8
    Image:         busybox
    Image ID:      docker-pullable://busybox@sha256:a5d0ce49aa801d475da48f8cb163c354ab95cab073cd3c138bd458fc8257fbf1
    Port:          <none>
    Host Port:     <none>
    Command:
      sh
      -c
      while true; do echo 'Logging...'; sleep 10; done
    State:          Running
      Started:      Tue, 04 Feb 2025 13:49:26 +0700
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-dmx2c (ro)
...
```

As you can see above we have 2 containers with name `nginx` and `logger`.

We can get the container logs using this command below.

```bash
➜ kubectl logs pods/nginx-with-logger logger 
Logging...
Logging...
Logging...
Logging...
Logging...
Logging...
```

The command above will print logs from pod `nginx-with-logger` specifically in container `logger`. To print logs from all container we can add option `--all-containers=true`.

## Access the Pod

To access the pod we can use `kubectl port-forward` command.

```bash
➜ kubectl port-forward nginx-with-logger 8080:80  
Forwarding from 127.0.0.1:8080 -> 80
Forwarding from [::1]:8080 -> 80
```

This command will forward traffic from port `8080` in our local machine to pod named `nginx-with-logger` port `80`.

Lets try to access it using `curl` and we should see default response from nginx server.

```bash
➜ curl http://localhost:8080
```

```html
<!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>
```

## Delete Pod

To delete pod we can use `kubectl delete pods <pod-name>` command.

```bash
➜ kubectl delete pods nginx
pod "nginx" deleted
```

## References

* <https://kubernetes.io/docs/concepts/workloads/pods/>
* <https://kubernetes.io/docs/reference/kubectl/generated/kubectl_run/>
* <https://kubernetes.io/docs/reference/kubectl/generated/kubectl_port-forward/>
* <https://kubernetes.io/docs/reference/kubectl/generated/kubectl_logs/>


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