AWS NACL — Subnet-Level Security in AWS 🔐

📅 Day 14 | AWS NACL — Subnet-Level Security in AWS 🔐

NACL (Network Access Control List) is a subnet-level firewall in AWS VPC, controlling traffic at the subnet boundary. Mastering NACLs is crucial for building secure cloud architectures, as they act as a security gate for each subnet.

🔥 Why NACL Is Important in AWS & DevOps

NACLs address the limitations of stateful firewalls like Security Groups by providing stateless inspection and granular control at the subnet level. Without NACLs, organizations risk exposing internal resources to unintended network access, potentially leading to data breaches and compliance violations, costing millions in remediation and fines.

Key Insights

• Stateless inspection: NACLs require explicit rules for both inbound and outbound traffic.
• ALLOW and DENY rules: NACLs support both allowing and denying traffic, offering flexibility in security policy enforcement.
• Terraform integration: Infrastructure-as-code tools like Terraform enable automated NACL management for consistent and repeatable deployments.

Working Example

resource "aws_network_acl" "public_nacl" {
vpc_id = aws_vpc.main.id
tags = {
Name = "public-nacl"
}
}
resource "aws_network_acl_rule" "allow_http_in" {
network_acl_id = aws_network_acl.public_nacl.id
rule_number = 100
egress = false
protocol = "6" # TCP
rule_action = "allow"
cidr_block = "0.0.0.0/0"
from_port = 80
to_port = 80
}
resource "aws_network_acl_rule" "allow_https_in" {
network_acl_id = aws_network_acl.public_nacl.id
rule_number = 110
egress = false
protocol = "6"
rule_action = "allow"
cidr_block = "0.0.0.0/0"
from_port = 443
to_port = 443
}

Practical Applications

• E-commerce platform: A company like Shopify can use NACLs to restrict database access to only application servers within a private subnet.
• Pitfall: Incorrectly configured NACL rules can inadvertently block legitimate traffic, causing service outages and impacting user experience.

References:

• https://dev.to/sudarshan_yadav/day-14-aws-nacl-subnet-level-security-in-aws-22lj