Readme updates

Author: opensource4learn

README.md

@@ -3,9 +3,11 @@ Terraform AWS VPC Module by Source4Learn(An Opensource Community to learn and sh
 ![Source4Learn](https://github.com/opensource4learn/terraform-aws-vpc/blob/main/s4l.png?raw=true)
 
 ## AWS VPC Module
-This AWS VPC Module will create following resources:
-- Subnets ["Public", "Private", "Storage"]
-- Route Tables ["Public", "Private", "Storage"]
+This AWS VPC module is designed to implement the common AWS infrastructure patterns such as single or multi-tier. The multi-tier patterns allow users to create infrastructure in separate layers as per the needs of modern applications.
+
+AWS VPC Module will create following resources:
+- VPC and Subnets
+- Route Tables
 - Security Gruoups
 - Internet Gateway
 - NAT Gateway
@@ -31,6 +33,28 @@ module "vpc" {
 }
 ```
 
+# AWS VPC multi-tier architecture
+The AWS resources created in the public layers can be accessed publicly(i.e. - frontend servers, load-balancers, bastion instances, etc) but backed resources such as application servers, database, caching servers will remain in private sections. The AWS infrastructure patterns can be categories as follows:
+
+
+- **Public Layer:** This layer consists of public subnets and has one subnet on each availability zone for high availability.
+- **Application Layer:** This layer of AWS infrastructure contains the private subnets and one on each Availability Zone.
+- **Database Layer:** The third layer consists of 3 private subnets and the same subnet on each availability zone.
+
+Let's take a brief overview of multi-layers or multi-tier architecture. It basically divides the AWS infrastructure into layers like - Public, Private, and Storage(Isolated database) layers. The reason behind this implementation is to protect and isolate private layers from any unwanted public access. In other words, the Public layer provides a shield to internal layers of architecture.
+
+AWS allows users to create the multi-tier infrastructure and distribute it across the availability zones of the current region to achieve the high availability of resources. 
+
+## 3-tier architecture
+To split the AWS infrastructure into multiple tiers and availability zones, please refer to below architectural diagram:</br>
+**Information yet to be added.
+
+## 2-tier architecture
+**Information yet to be added.
+
+## 1-tier architecture
+**Information yet to be added.
+
 ## Requirements
 
 | Name | Version |