2.1.4. DNS in VPCs (Route 53 Resolver)

DNS (Domain Name System) within VPCs, managed by Route 53 Resolver, is fundamental for hostname resolution between AWS resources and on-premises networks, enabling seamless communication in hybrid cloud environments.

Scenario: You need to enable instances in your AWS VPC to resolve hostnames for servers in your on-premises data center (e.g., server.onprem.local) and vice versa.

DNS is a critical component of any network, translating human-readable hostnames into IP addresses. In AWS, Amazon Route 53 Resolver provides DNS resolution for your VPCs and enables seamless hybrid DNS functionality.

Key Concepts of DNS in VPCs with Route 53 Resolver:

• VPC DNS (Default): Each VPC has a default DNS server provided by AWS (VPC CIDR + 2) for resolving Amazon-provided DNS hostnames (e.g., ec2-192-0-2-44.compute-1.amazonaws.com) and public DNS records.
• Private Hosted Zones (Route 53): Allow you to manage custom domain names for your VPC without exposing them to the public internet. You can define custom domain names (e.g., internal.example.com) that resolve only within your VPC or connected networks.
• Route 53 Resolver: A feature of Amazon Route 53 that enables DNS queries between your VPCs and your on-premises network.
  • Endpoint: Deploys Resolver endpoints (with ENIs) in your VPC to enable DNS queries to/from on-premises.
  • Rules: Create forwarding rules to send queries for specific domains (e.g., onprem.com) to on-premises DNS servers, or inbound rules to allow on-premises to query AWS VPC DNS.
• Use Cases: Hybrid DNS resolution, VPC Peering DNS resolution, Transit Gateway DNS resolution.

Practical Implementation: Configuring Route 53 Resolver Outbound Endpoint and Rule

# Assuming VPC_ID and subnet IDs are defined for Resolver ENIs
# 1. Create an Outbound Resolver Endpoint
OUTBOUND_ENDPOINT_ID=$(aws route53resolver create-resolver-endpoint \
  --name MyOutboundResolver \
  --direction OUTBOUND \
  --security-group-ids sg-0abcdef1234567890 \
  --ip-addresses SubnetId=subnet-0a1b2c3d,Ip=10.0.1.10 \
  --query ResolverEndpoint.Id --output text)
echo "Outbound Resolver Endpoint ID: $OUTBOUND_ENDPOINT_ID"

# 2. Create a Resolver Rule to forward on-premises queries
RULE_ID=$(aws route53resolver create-resolver-rule \
  --name OnPremisesForwardingRule \
  --rule-type FORWARD \
  --domain-name onprem.local \
  --target-ips Ip=192.168.1.100 \
  --resolver-endpoint-id $OUTBOUND_ENDPOINT_ID \
  --query ResolverRule.Id --output text)
echo "Resolver Rule ID: $RULE_ID"

# 3. Associate the Resolver Rule with your VPC
aws route53resolver associate-resolver-rule \
  --resolver-rule-id $RULE_ID \
  --vpc-id $VPC_ID

⚠️ Common Pitfall: Forgetting to configure security groups for Resolver endpoints to allow DNS traffic (UDP/TCP port 53) from/to relevant networks.

Key Trade-Offs:

• Simplicity (Default DNS) vs. Hybrid Functionality (Resolver): Default VPC DNS is simple but limited to AWS-internal and public resolution. Route 53 Resolver adds complexity but enables seamless hybrid DNS.

Reflection Question: How does DNS (Domain Name System) within VPCs, specifically utilizing Route 53 Resolver with its endpoints and rules, fundamentally enable seamless hostname resolution between AWS resources and on-premises networks in hybrid cloud environments?