Merge pull request #2 from source4learn/mr-alpha

Readme Update

Author: opensource4learn

README.md

@@ -1,11 +1,13 @@
 # Hashicorp Terraform AWS VPC Module
-Terraform AWS VPC Module by Source4Learn(An Opensource Community to learn and share knowledge)
-![Source4Learn](https://github.com/opensource4learn/terraform-aws-vpc/blob/main/s4l.png?raw=true)
+Terraform AWS VPC Module by Source4Learn(Source4Learn is an opensource learning community.)
+![Source4Learn](https://github.com/source4learn/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 Terraform 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
@@ -21,8 +23,8 @@ provider "aws" {
 }
 
 module "vpc" {
-  source                = "opensource4learn/vpc/aws"
-  version               = "0.1.0-beta"
+  source                = "source4learn/vpc/aws"
+  version               = "0.1.1"
   cluster_prefix        = "source4learn"
   cluster_environment   = "development"
   cluster_architecture  = "3-tier"
@@ -31,6 +33,55 @@ module "vpc" {
 }
 ```
 
+# AWS Multi Layer 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, databases, 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 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.
+
+To split the AWS infrastructure into multiple tiers and availability zones, please refer to below architectural diagram:</br>
+![VPC](https://github.com/source4learn/terraform-aws-vpc/blob/main/vpc.png?raw=true)
+
+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
+A three-tier architecture pattern help will help to design a highly secured, modular, scalable, and fault-tolerant infrastructure. In this approach, the application infrastructure will be divided into a public layer, business logic, and storage layer. The resources in the individual layer are being created separately and they can communicate with specific pre-defined routes and security rules.
+
+Use this approach while implementing a microservices-based application architecture. The internet-facing services like - Frontend servers and bastion instances can be created public layer, app servers can be created in the intermediate application layer, and storage layer can have data services such as databases/caching etc.
+
+This AWS Terraform module will help you to create an AWS VPC with 3-tier by just passing `cluster_architecture` as `3-tier`. Users also need to define the desired VPC size in form of `cidr` and subnet mask as `subnet_bits`.
+
+*Example:* Let's assume that the user needs to create a VPC network with ~4000 hosts available and each subnet should have 254 IP addresses. So the cidr value for vpc would be `x.x.x.x/20` and the expected value for subnet would be `x.x.x.x/24`. But in this Terraform module, it accepts subnet mask value as subnet bits which can be calculated by subtracting the subnet cidr value with vpc cidr value.
+
+```
+cluster_architecture  = "3-tier"
+cidr                  = "10.0.0.0/20"
+subnet_bits           = "4"
+```
+
+## 2-tier architecture
+The two-tier pattern is suitable for that application architecture which requires the isolation between the presentation and business logic without increasing the complexity of application infrastructure.
+
+```
+cluster_architecture  = "2-tier"
+cidr                  = "10.0.0.0/20"
+subnet_bits           = "4"
+```
+
+## 1-tier architecture
+This single tier architecture can be used for monolythic infrastructures(Highly in-secure) and test/devlopment environments.
+
+```
+cluster_architecture  = "1-tier"
+cidr                  = "10.0.0.0/20"
+subnet_bits           = "4"
+```
+
 ## Requirements
 
 | Name | Version |
@@ -74,3 +125,14 @@ module "vpc" {
 | Name | Description |
 |------|-------------|
 | <a name="output_vpc_id"></a> [vpc\_id](#output\_vpc\_id) | Terraform Output |
+
+## Summary
+
+If you encounter an error or problem in this setup, please report in the GitHub repository issues.</br>
+Reach us in case you need any further assistance.
+
+Email: source4learn@gmail.com
+
+Twitter: ![@source4learn](https://twitter.com/source4learn/)
+
+LinkedIn: ![linkedin.com/in/source4learn](https://www.linkedin.com/in/source4learn/)