AWS Cloud Subnet and Access

In Amazon Web Services (AWS), subnets are subdivisions of a Virtual Private Cloud (VPC) IP address range where you can place groups of resources. Subnets allow you to segment and organize your network resources within a VPC. Additionally, controlling access to resources within subnets is crucial for network security. Let's explore subnets and access control in AWS:

Subnets in AWS:

1. Definition:

   • A subnet is a range of IP addresses in your VPC.
   • Subnets are created within a VPC and are associated with a specific availability zone.

2. IP Addressing:

   • Subnets have their own IP address range, a subset of the overall VPC CIDR block.

3. Public and Private Subnets:

   • Public Subnet: Typically associated with resources that need direct access to the internet. Instances in a public subnet might have Elastic IP addresses or public IP addresses.
   • Private Subnet: Reserved for resources that do not require direct internet access. Instances in a private subnet can access the internet through a Network Address Translation (NAT) gateway or NAT instance.

4. Route Tables:

   • Each subnet is associated with a route table, which controls the traffic leaving the subnet.
   • Public subnets typically have a route to an Internet Gateway (IGW) for direct internet access.

5. Network ACLs and Security Groups:

   • Network ACLs (NACLs): These act as a firewall for controlling traffic in and out of a subnet.
   • Security Groups: These are stateful firewalls associated with instances. They control inbound and outbound traffic at the instance level.

Access Control in AWS:

1. Security Groups:

   • Definition: Security Groups act as virtual firewalls for your instances.
   • Inbound Rules: Define what traffic is allowed to reach your instances.
   • Outbound Rules: Define what traffic is allowed to leave your instances.

2. Network ACLs (NACLs):

   • Definition: NACLs are stateless and control traffic at the subnet level.
   • Inbound and Outbound Rules: Specify rules for allowing or denying traffic based on IP addresses, protocols, and ports.

3. Route Tables:

   • Definition: Route tables determine where network traffic is directed.
   • Public and Private Routes: Define routes to IGW for public subnets and NAT gateways or instances for private subnets.

4. Internet Gateway (IGW):

   • Definition: An IGW allows communication between instances in your VPC and the internet.
   • Associated with Public Subnets: Typically associated with public subnets to enable direct internet access.

5. NAT Gateway or NAT Instance:

   • Definition: NAT gateways or instances enable instances in private subnets to initiate outbound traffic to the internet while preventing inbound traffic.
   • Private Subnet Access: Used for instances in private subnets that need internet access (e.g., for software updates).

6. Elastic IP Addresses (EIPs):

   • Definition: EIPs are static IP addresses that can be associated with instances in a VPC.
   • Public IP Addresses: Instances in a public subnet can have public EIPs or public IPs.

7. VPN and Direct Connect:

   • VPN (Virtual Private Network): Provides secure communication between your on-premises data center and your VPC.
   • Direct Connect: Offers dedicated network connections between your on-premises environment and AWS.

8. Amazon VPC Peering:

   • Definition: VPC peering allows communication between instances in different VPCs.
   • Inter-VPC Connectivity: Enables resource sharing and communication between different VPCs.

9. AWS PrivateLink:

   • Definition: AWS PrivateLink allows access to services over the AWS backbone network rather than the public internet.
   • Secure Access: Enhances security by avoiding exposure to the public internet.