Intro to pods

rosehgal · Sep 26, 2020 · ed24b99 · ed24b99
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diff --git a/README.md b/README.md
@@ -11,7 +11,7 @@ This is not exclusive guide to learn Kubernetes from scratch, rahter this is jus
  - **kubeadm**
  - **kubelet**
  - **kubectl**
-1. **Kuberenetes pods**: How are they different than Docker containers.
+1. [**Kuberenetes pods**](#Kubernetes-pods): How are they different than Docker containers.
  - Moving from Docker container to Kubernetes pods.
 1. **Kubernetes Resource**:
  - Pods
@@ -133,3 +133,112 @@ Kubernetes runs in client server model, similar to the way the docker runs. Kube
  - Runs in Worker nodes.
  - Runs task over worker nodes.
  - Maintain Pod lifecycle. Not just for pods, but all Kubernetes resources lifecycle.
+
+## Kubernetes pods
+
+- Pods run multiple containers.
+- Pods abstract out multilpe containers into single unit.
+- If two service in pods are both exposing service on same port, the other one wont spin up and it will fail.
+- The unit of Kubernetes work load is called Pod. 
+
+### How to create a pod
+You can create a simple nginx pod with following yaml spec. Save this in file name : [pod.yml](pod.yml)
+```yaml
+apiVersion: v1
+kind: Pod
+metadata:
+ name: nginx
+spec:
+ containers:
+ - name: nginx
+ image: nginx
+```
+|Key name| Key Description|
+|---|---|
+|`apiVersion`|Kubernetes server API| 
+|`kind`|Kubernetes Resource type: `Pod`| 
+|`metadata.name`|Name of Kubernetes Pod|
+|`spec.container.name`|Name of Container which will run in a Pod|
+|`spec.container.name`|Name of docker image to run| 
+
+Run this Pod spec with. `kubectl apply -f pod.yml`
+```bash
+root@vagrant:/home/vagrant/kubedata# kubectl apply -f pod.yaml
+pod/nginx created
+
+# If everything goes OK, you will se something like this.
+
+root@vagrant:/home/vagrant/kubedata# kubectl get pods
+NAME READY STATUS RESTARTS AGE
+nginx 1/1 Running 0 43s
+root@vagrant:/home/vagrant/kubedata#
+```
+
+1. Running command into container, running inside Pod. `kubectl exec -it <pod_name> -c <container_name> -- <command>`
+ ```
+ root@vagrant:/home/vagrant/kubedata# kubectl exec -it nginx -c nginx -- whoami
+ root
+
+ root@vagrant:/home/vagrant/kubedata# kubectl exec -it nginx -c nginx -- /bin/sh
+ # cat /etc/*-release
+ PRETTY_NAME="Debian GNU/Linux 10 (buster)"
+ NAME="Debian GNU/Linux"
+ VERSION_ID="10"
+ VERSION="10 (buster)"
+ VERSION_CODENAME=buster
+ ID=debian
+ HOME_URL="https://www.debian.org/"
+ SUPPORT_URL="https://www.debian.org/support"
+ BUG_REPORT_URL="https://bugs.debian.org/"
+ ```
+1. Running multiple container in one pod.
+ ```yaml
+ apiVersion: v1
+ kind: Pod
+ metadata:
+ name: nginx
+ spec:
+ containers:
+ - name: nginx
+ image: nginx
+ - name: curl
+ image: appropriate/curl
+ stdin: true
+ tty: true
+ command: ["/bin/sh"]
+ ```
+ Save this into [pod-with-two-containers.yml](files/pod-with-two-containers.yml). 
+ Run this : `kubectl apply -f pod-with-two-containers.yml`
+1. Delete a running pod. `kubectl delete -f pod-with-two-containers.yml`. This will remove the pod mentioned in spec file.
+1. Container in a Pod can connect to another container in same pod with `spec.containers.name`.
+ ```bash
+ root@vagrant:/home/vagrant/kubedata# kubectl exec -it nginx -c curl -- /bin/sh
+ # curl nginx
+ <!DOCTYPE html>
+ <html>
+ <head>
+ <title>Welcome to nginx!</title>
+ <style>
+ 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:https://nginx.org/">nginx.org</a>.<br/>
+ Commercial support is available at
+ <a href="http:https://nginx.com/">nginx.com</a>.</p>
+
+ <p><em>Thank you for using nginx.</em></p>
+ </body>
+ </html>
+ #
+ ```
+
diff --git a/files/pod-with-two-containers.yml b/files/pod-with-two-containers.yml
@@ -0,0 +1,13 @@
+apiVersion: v1
+kind: Pod
+metadata:
+ name: nginx
+spec:
+ containers:
+ - name: nginx
+ image: nginx
+ - name: curl
+ image: appropriate/curl
+ stdin: true
+ tty: true
+ command: ["/bin/sh"]
diff --git a/files/pod.yml b/files/pod.yml
@@ -0,0 +1,8 @@
+apiVersion: v1
+kind: Pod
+metadata:
+ name: nginx
+spec:
+ containers:
+ - name: nginx
+ image: nginx