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# Scalable App Deployment with AWS

Let's say we have a web application named `MyApp` and we want to deploy it to AWS in a scalable fashion. How do we do it?

## Walkthrough

![](https://299721776-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LBPk9Ii0WH-txgubgY2%2F-LBPkEsjuKBT4BqsRiAN%2F-LBPkScKZCp1Z4UWTHDt%2Faws_deployment_1.png?generation=1525162304466260\&alt=media)

As described in above diagram the deployment architecture of AWS consist of following components:

### VPC

* MyApp VPC
  * All EC2 instances are placed inside MyApp VPC for security purposes. MyApp VPC consists of 4 subnets:
    * Private-1a (Private subnet in AZ- 1a)
    * Private-1b (Private subnet in AZ- 1b)
    * Public-1a  (Public subnet in AZ- 1a)
    * Public-1b (Public subnet in AZ- 1b)
  * `Private Subnet` - Outer services can not access the instance directly. The instances do not have a public IP. Whereas, the instances themselves can access the internet and any outer services via NAT Internet Gateway.
  * `Public Subnet` - Outer Services can access such instances directly through their public IP.
* Database Layer
  * A single node of MongoDB instance will suffice for MyApp.
  * It can be a Primary Node hosted in Private Subnet of VPC.
  * A sample setup may look like:
    * MongoDB - `PrimaryNode`
      * Availability Zone: `ap-southeast-1a`
      * Instance Size : `M3.medium (1 vCPU, 3.75GB RAM, 60GB EBS, Volume attached)`

#### Aiming Higher

For High Availability (HA) there should be one more DB instance in another Availability Zone (AZ) i.e **1b** which can act as the replica for `PrimaryNode`.

### Application Layer

* MyApp NodeJS Application Layer
  * This layer Exists in `Private Subnets` (1a, 1b) of VPC i.e they are not directly accessible like DB layer.
  * This is the layer where MyApp is deployed via AWS EC2 Container Service.
  * A sample `Single EC2 instance` configuration in this layer:
    * Instance Size : `T2.micro (1 vCPU, 1GB RAM, 20GB EBS)`
  * The instances are kept in an `AutoScaling Group` where desired Instances are 2 and `ECS Service` desired Running tasks are 2.
  * Count is kept at 2 deliberately, for smooth deployment. 

### LoadBalancer

LoadBalancer (LB) is hosted in Public Subnets of VPC For High Availability. Ports 80 & 443 of LB are mapped with port 3000 of EC2 instances running MyApp.

### CloudFront

CloudFront is placed for caching the static contents like JS and CSS files next to the LB which will serve them and reduce requests to the Original source.