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.

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Last update: 2025-06-07 06:04