Secure servercommunication: Isolation and controlled exposure¶
Unrestricted communication between servers increases the attack surface. A compromised instance can pivot laterally, escalating access to sensitive systems. Proper network segmentation limits blast radius and enforces least-privilege principles.
Network isolation¶
Private Subnets:
Deploy backend services (e.g., databases, APIs) in private subnets with no public IPs.
Use NAT gateways for outbound traffic if needed.
VPC/VNet Peering: For cross-account/team communication, use private peering (AWS VPC, Azure VNet) instead of public routes.
Example (AWS):
aws ec2 create-vpc-peering-connection --vpc-id vpc-123 --peer-vpc-id vpc-456
Service-specific exposure¶
Public-Facing Services Only:
Expose only load balancers (ALB/NLB) or API gateways publicly.
Backend servers (e.g., app logic, databases) should never be directly internet-accessible.
Security Groups & NACLs: Restrict ingress/egress to specific IPs and ports.
Example (AWS SG rule):
aws ec2 authorize-security-group-ingress \
--group-id sg-123 \
--protocol tcp \
--port 443 \
--cidr 203.0.113.0/24
Zero Trust for internal traffic¶
Mutual TLS (mTLS): Require certificate-based auth between services (e.g., Istio, Linkerd).
Service Meshes: Enforce policies like “Service A can only talk to Service B on port 8080” (Cilium, Calico).
Monitoring & enforcement¶
Flow Logs: Log all traffic (AWS VPC Flow Logs, Azure NSG Flow Logs) to detect anomalies.
Automated Policy Checks: Tools like AWS Config or Azure Policy can flag overly permissive rules.
Implementation checklist¶
Isolate internal services in private subnets.
Expose minimally: Only public endpoints get internet access.
Encrypt internal traffic (TLS, mTLS).
Monitor traffic patterns for deviations.
Example Architecture:
Public Internet → [Load Balancer] → [Private Subnet: App Servers] → [Private Subnet: Database]
When to break isolation (carefully)¶
DevOps access: Use SSM Session Manager (AWS) or Bastion Hosts (with MFA) for admin access.
Hybrid clouds: Site-to-site VPNs or Direct Connect for on-premises links.