Add pods exercise

002_0_pods/.gitignore

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+.idea
+*.iml
+
+node_modules/

002_0_pods/.prettierrc

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+{
+  "printWidth": 120
+}

002_0_pods/Dockerfile

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+FROM node:12
+
+COPY . .
+WORKDIR .
+
+RUN npm install
+ENTRYPOINT ["npm", "start"]

002_0_pods/Makefile

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+docker-build:
+	cd node-app && docker build . -t robinnagpal/kubernetes-tutorial-001-node-app
+docker-push:
+	docker push robinnagpal/kubernetes-tutorial-001-node-app

002_0_pods/README.md

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+# What are Pods
+Pod is a "co-located" group of containers abd represents a basic building block in Kubernetes. We don't
+deploy containers individually, we always deploy pods of container/s 
+
+# Why do we need Pods
+## One vs Multiple Containers
+* Containers are designed to run only a single process per container
+* Disadvantages of running multiple processes in a container
+    * You have to manage processes your self
+    * If all processes write to standard output, it then difficult to separate the logs
+    * Difficult to add logic to restart if one of the process dies
+
+
+# Two individual containers vs two containers in a Pod
+
+## Two individual containers
+* Port mappings ad added to the host machine which makes it difficult to replicate since the post mappings 
+need to be unique for each replica
+
+## Two containers in a Pod
+* Pods help provide the two containers running in the same Pod the 
+same env as if they are running in the same pod . ???    
+* Containers are partially isolated
+    * Containers in a pod share the same Linux Namespace instead of each container having its own
+    * Kubernetes achieves this by configuring Docker to not create separate namespaces
+    * Containers run under the same Network and UTS namespace i.e. that share the same hostname
+    * Containers run under the same IPC namespace and can communicate through IPC
+    * Containers in the same Pod can also share the same PID namespace
+* Port mappings are done to the pod making it easy to create replicas of the pods
+* File systems of each container is isolated from the filesystem of other containers in the pod 
+Questions
+ - Do containers don't have separate namespace when running in pods?
+
+# Pod Networking
+When pod is create
+* It gets its own namespace
+* It gets its own virtual ethernet connection( --- does this refer to IP?)
+
+A pod is like a host as it has IP address and a range of ports that it can be mapped to container pods.
+IP of the pod is reachable from all other pods in k8s cluster
+
+# When do you need multiple containers
+* Backups
+* Synchronizer
+* Authentication Gateway
+* Collecting and pushing the logs
+
+
+# Connecting to Pod
+* Using k8s port forward
+`kubectl port-forward kubia-manual 8888:8080`
+* Using services
+
+
+# Using labels to organize pods
+* Organizing pods and all other Kubernetes objects is done through labels
+* ----- Show Kubernetes Pod file -------
+* Listing pods with labels `kubectl get po -l app=admin-ui`
+
+# Stopping and removing pods
+*  Delete by name - `kubectl pod delete nginx`
+*  Delete by label - `kubectl pod delete po -l env=dev`
+
+
+
+Other Networking Concepts
+* Every pod has an IP address
+* 
+https://unix.stackexchange.com/a/183722

002_0_pods/index.ts

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+import { createServer, IncomingMessage, ServerResponse } from "http";
+import { hostname } from "os";
+
+const port = 8080;
+const server = createServer((request: IncomingMessage, response: ServerResponse) => {
+  switch (request.url) {
+    case "/node-app": {
+      if (request.method === "GET") {
+        response.setHeader("Connection", "close");
+        response.end(`Hello world from ${hostname()}`);
+      }
+      break;
+    }
+    default: {
+      response.statusCode = 404;
+      response.end("Unknown path");
+    }
+  }
+});
+
+server.listen(port);

002_0_pods/package.json

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+{
+  "name": "app",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "start": "ts-node index.ts"
+  },
+  "author": "",
+  "license": "ISC",
+  "devDependencies": {
+    "@types/node": "^14.14.8"
+  },
+  "dependencies": {
+    "prettier": "^2.1.2",
+    "ts-node": "^9.0.0",
+    "typescript": "^4.0.5"
+  }
+}