Open Source Cloud and DevOps

VPC (Virtual Private Network)

VPC is a virtual network. Software defined network.

Features:

Every VPC has a internet gateway.
Network ACL, Route Table gets created.
One VPC can be across the multiple AZ in a region.
5 VPC, and 200 subnets per VPC
Public subnet EC2 machine has internet access.
NAT gateway is managed service. NAT instance is you have to manage yourself.
Network ACL is on the subnet level. Security Group applied at instance level.

To find the subnet, if public subnet or private subnet:

Check the route table for the subnet. If the Route Table has Internet Gateway mentioned, then the subnet is Public subnet. Otherwise, you would find a NAT gateway for the private subnet.

To check the ACL rules:

Check the Network ACL rules for the VPC, first rule is applied to the VPC.

Create a VPC

aws ec2 create-vpc --cidr-block 10.0.0.0/16 --no-amazon-provided-ipv6-cidr-block --dry-run

Create a Public Subnet

aws ec2 create-subnet --vpc-id vpc-xxxxx --cidr-block 10.0.10.0/26
aws ec2 create-internet-gateway
aws ec2 attach-internet-gateway --vpc-id vpc-xxxxx --internet-gateway-id idw-xxx
aws ec2 create-route-table --vpc-id vpc-xxxxx
aws ec2 create-route --route-table-id rtb-xxx --destination-cidr-block 0.0.0.0/0 --gateway-id igw-xxx

# confirmation
aws ec2 describe-route-tables --route-table-id rtb-xxx

# search subnets using queries and filters
aws ec2 describe-subnets --filters "Name=vpc-id,Values=vpc-xxx" --query 'Subnets[*].{ID:SubnetId,CIDR:CidrBlock}'

# associate subnet with route table
aws ec2 associate-route-table --subnet-id subnet-xxx --route-table-id rtb-xxx

# automatically assign public ip on instance launch
aws ec2 modify-subnet-attribute --subnet-id subnet-xxx --map-public-ip-on-launch

Create a Private VPC

aws ec2 create-subnet --vpc-id vpc-xxx --cidr-block 10.0.0.0/24
aws ec2 allocate-address --domain vpc --network-border-zones "availability zones, local zones"
aws ec2 create-nat-gateway --subnet-id subnet-xxx --allocation-id eipalloc-xxx
aws ec2 create-route-table --vpc-id vpc-xxx
aws ec2 create-route --route-table-id rtb-xxx --destination-cidr-block 0.0.0.0/0 --nat-gateway-id nat-xxx

Some points to consider:

VPC cannot be deleted directly, you need to delete the NAT gateway and route tables.
Also, remove the elastic IP associated with NAT gateway to make it public.