Routing Policies VS Routing Rules — AWS

Routing policies in Amazon Route 53 and Routing rules in Elastic Load Balancer (ELB). They serve different purposes and operate at different layers of your AWS architecture:

Routing Policies in Route 53

• Purpose: Route 53 routing policies determine how DNS queries are resolved and direct traffic to various endpoints based on different criteria.
• User Control: Users have significant control over how traffic is routed. You can choose from several routing policies to direct traffic:
• Simple Routing: Directs traffic to a single resource.
• Weighted Routing: Distributes traffic based on specified weights, allowing for controlled distribution among different resources.
• Latency-Based Routing: Routes traffic to the region that provides the lowest latency to the user.
• Geolocation Routing: Directs traffic based on the geographic location of the user making the DNS query.
• Geo proximity Routing: Routes traffic based on the geographic location of resources and, optionally, shifts traffic from one resource to another based on a bias value.
• Failover Routing: Automatically routes traffic to a backup resource if the primary one is unavailable.
• Multi-Value Answer Routing: Provides multiple IP addresses in response to DNS queries, improving availability by routing to healthy resources.

Routing Rules in ELB

• Purpose: ELB routing rules determine how traffic is distributed among the backend resources (like EC2 instances, containers, or IP addresses) once the DNS query has been resolved to the ELB.
• ELB Algorithms: ELBs use their own internal algorithms to distribute traffic among the targets:
• Round Robin: Classic Load Balancers (CLBs) use a round-robin algorithm to distribute incoming requests evenly across all healthy targets.
• Least Outstanding Requests: Application Load Balancers (ALBs) use this algorithm to forward new requests to the target with the fewest outstanding requests, which helps balance traffic based on the current load.
• Target Group Health Checks and Stickiness: ELBs can use health checks to determine if a target is healthy and should receive traffic. ELBs also support session stickiness (also known as session affinity), where traffic from a user session is consistently directed to the same target.

Key Differences

User Control vs. Automated Algorithms:

• Route 53 (User-Controlled): Users have direct control over how traffic is routed based on their selected routing policies. You decide which policies to apply and configure them based on your application’s needs.
• ELB (Automated Algorithms): ELB uses pre-defined algorithms to distribute traffic among healthy targets. Users have limited control over these algorithms; the primary control is through target group configuration, health checks, and stickiness settings.

Layer of Operation:

• Route 53: Operates at the DNS layer, determining how DNS queries are resolved to IP addresses or ELB endpoints based on routing policies.
• ELB: Operates at the transport/application layer, distributing traffic among backend resources (e.g., EC2 instances) after the DNS resolution has occurred.

Decision Points:

• Route 53: Decides at the DNS query level which endpoint a user should reach based on the configured routing policy.
• ELB: Decides at the transport/application level which specific backend target should handle the incoming request based on the ELB’s routing rules.

Conclusion

You have correctly understood the fundamental difference between routing policies in Route 53 and routing rules in ELB. Route 53 gives you more control over directing traffic based on high-level policies, while ELB focuses on efficiently distributing that traffic among backend resources using its own set of algorithms and rules. Both are essential for building robust, high-performance, and scalable AWS architectures.

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