Add deployment intro

README.md

@@ -12,15 +12,15 @@ This is not exclusive guide to learn Kubernetes from scratch, rahter this is jus
  - **kubelet**
  - **kubectl**
 1. [**Kuberenetes pods**](#Kubernetes-pods): How are they different than Docker containers.
- - Moving from Docker container to Kubernetes pods.
-1. **Kubernetes Resource**:
- - Pods
- - Deployment
- - Services
- - Replicaset
- - Namespaces
- - Context
- - Config
+ - [Moving from Docker container to Kubernetes pods.](#how-to-create-a-pod)
+1. [**Kubernetes Resource**](#kubernetes-resources):
+ - [Pods](#pods)
+ - [Deployment](#deployments)
+ - [Replicaset](#replicasets)
+ - [Services](#services)
+ - [Namespaces](#namespaces)
+ - [Context](#context)
+ - [Config](#config)
 1. **Kubernetes network manager**
  - I will pick up the plugin called [Flannel](https://github.com/coreos/flannel#flannel).
 1. **Stateless Workload**
@@ -142,7 +142,7 @@ Kubernetes runs in client server model, similar to the way the docker runs. Kube
 - 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)
+You can create a simple nginx pod with following yaml spec. Save this in file name : [pod.yml](files/pod.yml)
 ```yaml
 apiVersion: v1
 kind: Pod
@@ -242,3 +242,71 @@ root@vagrant:/home/vagrant/kubedata#
  #
  ```
 
+## Kubernetes Resources
+
+### Pods
+- Fundamental unit of k8s cluster.
+- Abstraction for container/multiple-containers, running under single name.
+- Discussed in detail : [here](#how-to-create-a-pod)
+
+### Deployments
+- A Deployment provides declarative updates for Pods.
+- The configuration state in `yml` file, defines how the pods will run in cluster. They can specify:
+ - Replicas
+ - Resource allocation
+ - Connection with Volumes etc.
+ - We will see example once we see [replicasets](#replicasets)
+
+### Replicasets
+1. Run deployments in replicas.
+2. Create [file](files/deployment-replica.yml) with following specification.
+ ```yaml
+ apiVersion: apps/v1
+
+ kind: Deployment
+ metadata:
+ name: nginx
+
+ spec:
+ replicas: 3
+ selector:
+ matchLabels:
+ app: nginx-app
+ template:
+ metadata:
+ labels:
+ app: nginx-app
+ spec:
+ containers:
+ - name: nginx
+ image: nginx
+ ```
+
+ Notice the difference.
+
+ ```diff
+ -- kind: Pod
+ ++ kind: Deployment
+
+ ++ spec:
+ ++ replicas: 3
+ ++ selector:
+ ++ matchLabels:
+ ++ app: nginx-app
+ ```
+3. Remove existing pods(if any) `kubectl delete pods --all`, and create deployment.
+ ```bash
+ root@vagrant:/home/vagrant/kubedata# kubectl apply -f deployment-replica.yml
+ deployment.apps/nginx created
+
+ root@vagrant:/home/vagrant/kubedata# kubectl get deployments
+ NAME READY UP-TO-DATE AVAILABLE AGE
+ nginx 0/3 3 0 7s
+
+ root@vagrant:/home/vagrant/kubedata# kubectl get deployments -w
+ NAME READY UP-TO-DATE AVAILABLE AGE
+ nginx 1/3 3 1 14s
+ nginx 2/3 3 2 20s
+ ```
+
+

files/deployment-replica.yml

@@ -0,0 +1,17 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+ name: nginx
+spec:
+ replicas: 3
+ selector:
+ matchLabels:
+ app: nginx-app
+ template:
+ metadata:
+ labels:
+ app: nginx-app
+ spec:
+ containers:
+ - name: nginx
+ image: nginx