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Transit Gateways are a new introduction within AWS architecture to connect different VPCs together to achieve a more controlled routing behavior. This was earlier being achieved by Transit VPC AWS architecture. Transit gateway is a regional object and can be understood as a centralized router to which different VPCs connect. AWS IAM can be used to allow access to users to a Transit Gateway. Presently at the time of writing this article, Maximum of  5000 Attachments are supported per Transit Gateway. Maximum of 5 Transit Gateway attachments are supported per VPC Following components are required to establish a Transit Gateway: ASN (Autonomous System Number) This is required to ensure routing between different AS number. Transit Gateway Attachments There are different ways to connect a VPC or an On-Premise devices to a Transit Gateway. These are called Attachments. There are 2 types of attachments: VPC Attachment VPCs can be attach...

NAT Instances & NAT Gateway NAT Instances & NAT Gateways are used to provide internet to Private Subnet instances. NAT Instances are similar to the EC2 Instances except that they are used for NAT predominantly. These are Amazon provided Amazon Linux AMIs configured to be used as NAT Instances. These are created in the Public Subnet to provide internet connectivity for instances in Private Subnet thus it is important to have the right route tables associated with the Private Subnets updated to point the internet routes towards these. Since these are internet instances so they are to be linked with the Security Groups just like any other EC2 instances to allow traffic towards these instances. Each EC2 instances perform Source/Destination checks by default i.e. the EC2 instance must be either the source or destination of the traffic flows it sends or receive. For NAT instance this needs to be disabled as NAT instance will not be source or destination but will only be per...

Virtual Private Cloud VPC   or  Virtual Private Cloud  as the name exemplifies is the private cloud which can be built on AWS. It comprises of: Subnet:  Subnet are smaller subnets within VPCs where in EC2 instances reside and are associated with a  Route Table . Route Table : These are tables which carries the next hop details for reaching a subnet. Main Route Table :   Route Table  by default. If a subnet is not associated with any  Route Table  it gets associated with  Main Route Table . Access Control List :  These are stateless and are defined at the subnet. These are defined to allow or deny a particular subnet/IP addresss from reaching the associated Subnet. These are to be defined bothways. Security Group :  These are stateful and are applied on every instance to permit or block the flows/subnets/IP addresses. Internet Gateway :  These are gateways which are applied to a VPC to allow connectivity to...