AKS Gateway Routing Path, Query, and Headers - Part 8

Setting up basic hostname routing is the first step, but modern applications demand more surgical precision when directing traffic. Part 8 of our Kubernetes Gateway API series dives deep into the advanced routing options that allow you to control traffic flow based on specific components of an incoming request: Path, Query Parameters, and Headers.

This guide provides a complete tutorial on how to implement these routing mechanisms on an Azure Kubernetes Service (AKS) cluster using the Gateway API.

Understanding Advanced Routing Options

The Kubernetes Gateway API offers several ways to match and forward traffic beyond simple hostnames:

1. Path Matching: The most common form of advanced routing, allowing traffic to be split based on the URL path.
2. Query Parameter Matching: Directing traffic based on specific parameters present in the query string (e.g., ?version=beta).
3. Header Matching: Routing decisions based on specific HTTP headers (e.g., matching a User-Agent to differentiate between mobile and desktop users).
4. Hostname Matching: The foundational routing based on the domain name, which the custom rules extend.
5. Default/Fallback Route: A crucial “catch-all” route that ensures no request results in a generic 404 error if none of the explicit rules match.

Implementing Path-Based Routing

Path routing can be configured with three main matching types:

• Prefix: Matches any path that begins with the configured value (e.g., /routing matches /routing and /routing/abc).
• Exact: Matches only if the path is exactly the configured value (e.g., /exact matches only /exact).
• Regular Expression (Regex): Offers the most powerful and flexible matching, allowing for complex pattern recognition in the path.

In the demonstration, setting a rule with a path prefix like /routing directs traffic to a specific backend application, while an exact path match only works when the URL is precisely defined.

Extending Routing with Headers and Query Strings

To implement sophisticated deployment strategies like A/B testing or internal feature access, you can combine path matching with checks against HTTP headers and query strings:

• Header Matching: A rule can be configured to send traffic to a second application (e.g., App #2) only if the path is matched and a specific header (e.g., Header: routing) is present. If the header is absent or has a different value, traffic falls to the next matching rule.
• Query String Matching: Similar to header matching, a rule can be set to direct traffic to a third application (e.g., App #3) if a specific query string (e.g., ?query=routing) is included in the request.

By chaining these rules in an HTTPRoute definition, you can establish complex logic to direct traffic to the correct service.

Using Custom Hostnames and Fallback Routes

The guide also covers two critical aspects of production readiness:

1. Custom Domain Integration: By simply adding a custom URL (like routing.programmingwithwolfgang.com) to the hostnames list on the HTTPRoute, you enable access via a custom domain. This relies on the Azure DNS zone being configured with a CNAME record pointing the custom URL to the AGFC’s public hostname.
2. Implementing a Default Route: To enhance user experience, a final, less-indented backendRef is added to the HTTPRoute that acts as a catch-all. If none of the specific path, header, or query rules are satisfied, the request is forwarded to a designated default application (e.g., App #4), preventing a generic 404 error. This ensures a consistent user experience with a helpful landing page or error message.

Conclusion

The Kubernetes Gateway API provides a powerful and flexible way to manage traffic, moving far beyond simple hostname resolution. By utilizing path, query, and header matching, you gain the ability to implement advanced DevOps strategies on AKS, such as precise A/B testing and seamless canary rollouts.

The key takeaways are:

• Keep routing rules as simple as possible to maintain clarity.
• Always include a default/fallback route to handle unmatched requests gracefully.
• Leverage external DNS records to easily use custom hostnames with your HTTPRoute definitions.

You can find all the code sample on GitHub.

This post was AI-generated based on the transcript of the video “AKS Gateway Routing Path, Query, and Headers - Part 8” and reviewed by me.

Video - AKS Gateway Routing Path, Query, and Headers - Part 8