So far, we’ve covered use cases that involve traffic to and from an existing on-premises data center. This section will review options to address situations where the traffic originates from various locations on the internet.
Application Load Balancer
When an Elastic Load Balancer is set up in an AWS Local Zone, it is done in much the same way as it is in any standard availability zone. First, unlike in a standard region, you only need to assign one subnet. Second, only the layer 7 Application Load Balancer (ALB) variant is available. Layer 4, or network load balancers (NLB), cannot be deployed to an AWS Local Zone.
Amazon Route53 for load balancing
Although ALB addresses layer 7 load-balancing use cases, some low-latency applications that get deployed in AWS Local Zones rely on UDP-based protocols, such as QUIC, WebRTC, and SRT, which can’t be load-balanced by layer 7 load balancers.
Figure 6.16 – Amazon Route53’s weighted routing policy for two WireGuard VPN servers
Fortunately, Amazon Route53 offers an alternative for such situations—weighted routing policies.
Weighted routing policies
These allow you to assign weights to multiple resources or endpoints, enabling a proportionate distribution of DNS responses among them. This is useful for load balancing, A/B testing, or gracefully migrating traffic from one resource to another. By assigning a different value to each resource, you determine the likelihood (or percentage) of traffic directed to each, giving you granular control over the distribution of incoming requests.
You can choose a value between 1 and 255 for the weight on each record. The percentage of traffic each one will respond to is evaluated on a relative basis across all of the weights. For example, the two records shown in the preceding figure each have a weight of 10. This means they are evenly weighted, so each one will respond 50% of the time. Giving each one a weight of 200 would have the same effect.
Amazon Route53’s weighted routing formula
The formula used to determine how much traffic a given record receives is as follows:
Examples are as follows:
Record 1 – Weight 10: 3.85%
Record 2 – Weight 250: 96.15%