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# VPC
- [VPC](#vpc)
- [VPC & Subnets Primer](#vpc--subnets-primer)
- [Internet Gateway & NAT Gateways](#internet-gateway--nat-gateways)
- [Network ACL & Security Groups](#network-acl--security-groups)
- [Network ACLs vs Security Groups](#network-acls-vs-security-groups)
- [VPC Flow Logs](#vpc-flow-logs)
- [VPC Peering](#vpc-peering)
- [VPC Endpoints](#vpc-endpoints)
- [Site to Site VPN & Direct Connect](#site-to-site-vpn--direct-connect)
- [Transit Gateway](#transit-gateway)
- [VPC Summary](#vpc-summary)
## VPC & Subnets Primer
- VPC -Virtual Private Cloud: private network to deploy your resources (regional resource)
- Subnets allow you to partition your network inside your VPC (Availability Zone resource)
- A public subnet is a subnet that is accessible from the internet
- A private subnet is a subnet that is not accessible from the internet
- To define access to the internet and between subnets, we use Route Tables.
## Internet Gateway & NAT Gateways
- Internet Gateways helps our VPC instances connect with the internet
- Public Subnets have a route to the internet gateway.
- NAT Gateways (AWS-managed) & NAT Instances (self-managed) allow your instances in your Private Subnets to access the internet while remaining private
## Network ACL & Security Groups
- NACL (Network ACL)
- A firewall which controls traffic from and to subnet
- Can have ALLOW and DENY rules
- Are attached at the Subnet level
- Rules only include IP addresses
- Security Groups
- A firewall that controls traffic to and from an ENI / an EC2 Instance
- Can have only ALLOW rules
- Rules include IP addresses and other security groups
### Network ACLs vs Security Groups
| Security Group | Network ACL |
| ------------------------------------------------------------------------------------------------------------------------------------------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------- |
| Operates at the instance level | Operates at the subnet level |
| Supports allow rules only | Supports allow rules and deny rules |
| Is stateful: Return traffic is automatically allowed, regardless of any rules | Is stateless: Return traffic must be explicitly allowed by rules |
| We evaluate all rules before deciding whether to allow traffic | We process rules in number order when deciding whether to allow traffic |
| Applies to an instance only if someone specifies the security group when launching the instance, or associates the security group with the instance later on | Automatically applies to all instances in the subnets it's associated with (therefore, you don't have to rely on users to specify the security group) |
<https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Security.html>
## VPC Flow Logs
- Capture information about IP traffic going into your interfaces:
- VPC Flow Logs
- Subnet Flow Logs
- Elastic Network Interface Flow Logs
- Helps to monitor & troubleshoot connectivity issues. Example:
- Subnets to internet
- Subnets to subnets
- Internet to subnets
- Captures network information from AWS managed interfaces too: Elastic Load Balancers, ElastiCache, RDS, Aurora, etc…
- VPC Flow logs data can go to S3 / CloudWatch Logs
## VPC Peering
- Connect two VPC, privately using AWS’ network
- Make them behave as if they were in the same network
- Must not have overlapping CIDR (IP address range)
- VPC Peering connection is not transitive (must be established for each VPC that need to communicate with one another)
## VPC Endpoints
- Endpoints allow you to connect to AWS Services using a private network instead of the public www network
- This gives you enhanced security and lower latency to access AWS services
- VPC Endpoint Gateway: S3 & DynamoDB
- VPC Endpoint Interface: the rest
## Site to Site VPN & Direct Connect
- Site to Site VPN
- Connect an on-premises VPN to AWS
- The connection is automatically encrypted
- Goes over the public internet
- On-premises: must use a Customer Gateway (CGW)
- AWS: must use a Virtual Private Gateway (VGW)
- Direct Connect (DX)
- Establish a physical connection between on-premises and AWS
- The connection is private, secure and fast
- Goes over a private network
- Takes at least a month to establish
## Transit Gateway
- For having transitive peering between thousands of VPC and on-premises, hub-and-spoke (star) connection
- One single Gateway to provide this functionality
- Works with Direct Connect Gateway, VPN connections
## VPC Summary
- VPC: Virtual Private Cloud
- Subnets:Tied to an AZ, network partition of the VPC
- Internet Gateway: at the VPC level, provide Internet Access
- NAT Gateway / Instances: give internet access to private subnets
- NACL: Stateless, subnet rules for inbound and outbound
- Security Groups: Stateful, operate at the EC2 instance level or ENI
- VPC Peering: Connect two VPC with non overlapping IP ranges, nontransitive
- VPC Endpoints: Provide private access to AWS Services within VPC
- VPC Flow Logs: network traffic logs
- Site to Site VPN: VPN over public internet between on-premises DC and AWS
- Direct Connect: direct private connection to AWS
- Transit Gateway: Connect thousands of VPC and on-premises networks together