Application Request Routing (ARR) affinity in Azure Web Apps and why it might not be the best choice for certain scenarios.
ARR affinity is a feature that enables “sticky sessions” by ensuring that subsequent requests from a client are routed to the same instance of a web app. While this can be useful in some cases, there are several reasons why you might want to avoid using ARR affinity:
- Scalability: Relying on ARR affinity can limit the scalability of your application. When new instances are added or removed, the load balancer may not distribute traffic evenly across all instances, leading to an imbalanced workload and potentially affecting performance.
- Resiliency: If an instance becomes unhealthy or fails, clients with an affinity to that instance may experience downtime or degraded performance until their session expires or they are manually redirected to a healthy instance.
- Statelessness: Modern cloud-native applications are often designed to be stateless, meaning they do not store any session-specific data on the server. Stateless applications can scale more easily and recover from failures more quickly. By using ARR affinity, you may be introducing statefulness into your application, which can make it more difficult to manage and maintain.
- Performance: ARR affinity can lead to performance bottlenecks, as some instances may receive a disproportionate amount of traffic. This can result in slower response times and a suboptimal user experience.
- Global Distribution: If your application is deployed across multiple regions, ARR affinity can limit the ability to distribute traffic efficiently. Users may be routed to instances in distant regions, resulting in increased latency and slower response times.
In summary, while ARR affinity can be useful in certain scenarios, it’s essential to consider the potential drawbacks and evaluate whether it’s the right choice for your application. Stateless applications, proper session management, and leveraging distributed caching solutions can help you build scalable, resilient, and high-performing web apps in Azure without relying on ARR affinity.