This article explores Destination Rules, their role in routing policies, and integration with Istio’s traffic management strategy for effective load balancing.
In this article, we explore Destination Rules, their function in managing routing policies, and how they integrate with Istio’s traffic management strategy. Destination Rules enable you to define policies that are applied after traffic is routed to a specific service, ensuring controlled distribution and effective load balancing.Previously, we demonstrated how Virtual Services can be configured to manage traffic distribution across different service versions. For instance, consider the following Virtual Service configuration for the reviews service:
In this example, 99% of the traffic is directed to the subset “v1” and 1% to the subset “v2”.
Subsets used in Virtual Services are defined in Destination Rules. These rules allow you to apply specific configurations to traffic after it has been routed to a service.
Subsets represent groups of service instances identified by labels on the respective pods. The following Destination Rule illustrates how subsets for the reviews service are declared:
By default, Envoy uses a round-robin load-balancing strategy. However, you can modify this behavior by specifying a traffic policy within a Destination Rule. The following example demonstrates a simple pass-through load-balancing policy:
If you require a different policy for a specific subset (for example, a random algorithm for subset “v2”), the global traffic policy can be overridden at the subset level. This flexibility enables you to apply a default policy across all subsets while tailoring specific configurations as necessary.
Destination Rules also support various security configurations such as enabling TLS at the client level. The following configuration sets up mutual TLS, ensuring secure communication between services:
Remember, the host field plays a crucial role in the Destination Rule. When using a short name (e.g., “reviews”), Istio interprets it relative to the rule’s namespace. To ensure that the rule correctly references the intended service, especially if it resides in a different namespace, always use the fully qualified domain name (FQDN).
The following configuration shows how to use FQDN to avoid potential misconfigurations:
Destination Rules provide a powerful way to control post-routing traffic behavior by defining subsets and applying specific load-balancing and security policies. They are an essential component in Istio’s traffic management architecture and are particularly useful in advanced routing scenarios.For further reading, consider these resources:
