How to proxy request to a specific upstream path when the upstream root path already exists by using `request-transformer` plugin

It is a common case that there are several routes pointing to one service. For example, assuming we are using an echo application as upstream and running it in http://kong.example for testing purpose. There is an existing service entity called exampleservice in Kong, and its URL parameter is defined as http://kong.example. And, we have a route entity with a path /example, and strip_path: true. This route will proxy requests to http://kong.example via Kong. Now, you’d like to enable a plugin only on http://kong.example/api/v1/secret. One method is to create another pair of service and route. But with Kong request-transformer plugin, you can realize it without creating a duplicated service entity of the same application.

This article shows how to create a dynamic route path by using the request-transformer plugin.

1. Define the route path in regex format in the Route entity and point this route to the service exampleservice.

   In versions prior to 3.x:

   /example/(?<g1>api/v1/secret)

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   In versions from 3.x onwards, regex paths have to be prefixed with ~:

   ~/example/(?<g1>api/v1/secret)

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2. Enable the request-transformer plugin for the route.

3. Set Config.Replace.Uri of the request-transformer plugin as below:

   /$(uri_captures.g1)

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4. Test the settings. The request is transformed and sent to /api/v1/secret to your application.

   curl -i {kong proxy}/example/api/v1/secret
   HTTP/1.1 200 OK
   ....
   
   HTTP/1.1 GET /api/v1/secret. <--- request URI has been transformed to /api/v1/secret
   (echo application shows which path has been accessed as above)

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