AWS firewall rules: 7 best practices for security that actually works
Firewall rules block or allow traffic. Get them wrong and either nothing works or attackers get in. Simple rules are better than complex ones.
1. Start with deny all
Default policy: block everything. Explicitly allow what you need.
Not the other way around (allow all, block bad things).
Explicit is safer.
2. Use security groups for layer 3-4
Security groups filter by source IP, port, protocol. Use them.
Allow only what's necessary. If a service needs port 443 from the internet, allow 443 from 0.0.0.0/0 (or more restrictive). Don't allow all ports.
3. Use Network Firewall for layer 7
Network Firewall reads domain names, SSL certificates, application content.
Block malware domains. Block admin panel access from non-admin networks. Layer 7 control.
4. Test before deploying
Create rules in a test environment first. Verify they work. Don't block legitimate traffic.
Test both inbound and outbound. Blocking outbound is easy to forget.
5. Log everything
Logging is essential for debugging and auditing. Enable flow logs on VPC, firewall rules, security groups.
When traffic is blocked, logs show why.
6. Review quarterly
Security posture changes. Rules accumulate. Delete old rules. Add new ones.
What made sense 2 years ago might not anymore.
7. Use tags and naming
Name rules clearly. "Allow SSH from bastion" is better than "rule 42."
Tag by environment, team, service. Makes management easier.
Where Critical Cloud comes in
Firewall rules are complex. Testing rule changes is hard. We validate rules work as intended.