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VPC Peering and Endpoints

Links: 101 AWS SAA Index

VPC Peering

  • Privately connect two VPC using AWS network.
  • Make them behave as if they were in the same network.
  • The VPCs can be in different region or accounts.
  • The CIDRs must not overlap.
  • VPC peering is not transitive. This means VPC peering must be enabled for each VPC that needs to communicate with each other.

    • So if there are 3 VPCs A, B and C. Peering is enabled between A B and B C. But since peering is not transitive A C are not peered.
  • We must update the route tables in each VPCs subnets to ensure EC2 instances can communicate with each other. This is very important.

    • Lets suppose the CIDR of VPC 1 is and the CIDR of VPC 2 is
    • In the route table of VPC1 we need to add this rule → send any traffic for to the peering connection
      • attachments/Pasted image 20220430100506.jpg
    • In the route table of VPC2 we need to add this rule → send any traffic for to the peering connection
      • attachments/Pasted image 20220430100535.jpg
  • We can reference a security group in a peered VPC.

Note that a VPC peering connection does not support edge to edge routing. This means that if either VPC in a peering relationship has one of the following connections, you cannot extend the peering relationship to that connection:
  • A VPN connection or an AWS Direct Connect connection to a corporate network
  • An Internet connection through an Internet gateway
  • An Internet connection in a private subnet through a NAT device
  • A gateway VPC endpoint to an AWS service; for example, an endpoint to Amazon S3.

VPC Endpoints

  • These are private endpoints within VPC that allow us to initiate a private connection to the AWS services. For example an instance in the private subnet can connect to S3 without going through the public internet.

    • attachments/Pasted image 20220430111219.jpg
  • VPC Endpoints are powered by AWS PrivateLink. So if the question doesn't mention Endpoints then you can go with PrivateLink.

  • They are redundant and scale horizontally.

Why use VPC Endpoint

  • Let's take the example of connecting to AWS SNS with and without VPC Endpoint.

    • Without VPC Endpoint: Option 1

      • Traffic goes from the private subnet to the NAT Gateway to the internet gateway and then to SNS over the public internet. This is possible since every AWS service has a public URL
      • This costs us a lot of money since the NAT Gateway has an hourly cost and everything goes through the public internet and we don’t get the best network performance.
    • With VPC Endpoint: Option 2

      • All the traffic stays private within the AWS network.
    • attachments/Pasted image 20220430111611.jpg

  • They remove the need of NATGW and IGW to access AWS services. This means you only need access to internet in the private subnet if you want to update the instances or if you are talking to services which are not inside AWS.

??? important] [Site to Site VPN]] and [[Direct Connect "[Site to Site VPN]] and [Direct Connect cannot access VPC endpoints. VPC endpoints are just to access AWS services privately within your VPC."

Types of Endpoints

Differences between interface and gateway endpoint.
  • Interface endpoint uses SG for security where as gateway endpoint uses endpoint policies.
  • You need to modify route tables for gateway endpoint, not needed for interface endpoint.

Interface Endpoint

  • It provisions an ENI (private IP address) as an entry point.

    • attachments/Pasted image 20220430112420.jpg
  • We must attach a security group to the ENI.

  • Supports most services
  • You pay an hourly rate for the provisioned end points.

Gateway Endpoint

  • Provisions a gateway that must be used as a target in a route table.

    • A Gateway Endpoint is a gateway that you specify as a target for a route in your route table for traffic destined to a supported AWS service.
  • It only supports 2 services S3 and DynamoDB.

    • You can use two types of VPC endpoints to access Amazon S3: gateway endpoints and interface endpoints
    • You can have both the endpoints independently in a VPC.
Endpoint policies control the security in case of gateway endpoint.
  • When you create a VPC endpoint, you can attach an endpoint policy that controls access to the service to which you are connecting.
  • An endpoint policy does not override or replace IAM user policies or service-specific policies (such as S3 bucket policies).
  • It is a separate policy for controlling access from the endpoint to the specified service.
Gateway endpoint is more cost efficient than interface endpoint.

Last updated: 2022-05-14