How to Use uriRegexRewrite in Istio VirtualService for Regex-Based URI Rewriting

If you’re struggling to use the newly merged regex rewrite feature (uriRegexRewrite) within your Istio virtual service, don’t worry! The key is understanding how to structure it properly according to the official Istio documentation.

Here’s an updated version of your VirtualService manifest that demonstrates the correct usage:

apiVersion: networking.istio.io/v1beta1
kind: VirtualService
metadata:
  labels:
    app.kubernetes.io/instance: authserver-webapi
  name: authserver-webapi
spec:
  gateways:
  - default
  hosts:
  - "auth.example.com"
  http:
  - match:
    # Match the base URI and any additional path segments after '/captcha-srv/' should be rewritten to just their contents, i.e., "/v1", "-/foo".
    uri: /captcha-srv(/|$)(.*)    
    rewrite: 
      uriRegexRewriteMatch: { regexp: "^\/captcha-srv((\/)|$)([^/\n]*)*" }       # Define a regular expression for the match. Matches '/captcha-srv/' and everything after it until reaching either another slash or end of line which would indicate no additional path segments are present.
      uriRegexRewrite: { rewrite:/\3                               # The third group in regex (parenthesized part within `()`) corresponds to the matched content without trailing '/captcha-srv'. This will be rewritten directly as `/v1`, for example, when a request comes like "/captcha-service/foo".
    route:
    - destination:
        host: captcha         # Specify where this rewrite should go. Assume 'captcha' is your service name hosting the actual content (without redirect).
        port:
          number: 80           # The TCP port on which Istio proxy listens for traffic going to services behind it, typically HTTP/HTTPS ports are used here when dealing with external applications like Nginx.

Here’s what each part does based on the provided content and instructions from official documentation:

• apiVersion: Specifies that this configuration is using Istio v1beta1 VirtualService specification (please refer to Istio API for updates).

• kind – Indicates the resource type, in our case a VirtualService which defines routing rules within an environment with service discovery and load balancing provided by Istio’s mesh network capabilities.

• The structure under ‘spec’, includes:

  • A reference to your gateway (if one is configured), otherwise using default.

• Under the HTTP traffic configuration, you specify a regex match pattern for URLs that need rewriting and then rewrite them with proper indentation as required by Istio YAML schema. Here we’ve specified /captcha-srv(/|$)(.*) which means any URL starting with this prefix should be matched regardless of what follows it (denoted using $() group).

  • The uriRegexRewriteMatch specifies the actual regular expression to match against incoming requests, capturing necessary parts for rewriting. Here { regexp: ... } defines a literal string as our complex Regex pattern—note that this example assumes your service name has ‘captcha-srv’ and expects at least one additional path segment after it (if any).

  • The uriRegexRewrite directive then takes what was captured by the regex within its parentheses (\3) as a template for our rewrite. This is where we strip away anything before /captcha-srv/ and retain only necessary segments, which Istio will use to redirect traffic correctly when requests come in with such URLs (e.g., rewrites “/capthappy” into just “v1”).

This setup ensures that incoming requests are matched against the specified regex pattern then processed through a rewrite mechanism where captured portions of URIs determine their final routing, effectively transforming them as required for your application logic—with Istio doing all heavy lifting behind scenes. Remember to align with official documentation and adjust configurations based on real service naming conventions and expected URL structures within the mesh network environment you’m deploying in.

By following these examples precisely, requests arrive at /captcha-service will be correctly redirected internally without alteration of protocol or ports (unless specified), ensuring a seamless flow through your application stack as intended by Istio with its robust routing capabilities enhanced for service discovery and load balancing. Always double-check the current version’se specifications in Istio Documentation before applying these configurations to match them up against evolving API versions or feature sets available at your time of deployment.