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Proxy API Requests

Most modern Web applications use APIs to get information for display, to trigger actions or to check if a user is authorized to see or do stuff. Those APIs may be part of your application (i.e. you have written it) or a third-party service running elsewhere. Wherever they run – our favorite spot for them is behind Couper :)

Let's create a Couper configuration that exposes two backend services in a consolidated API for the client.

Configuration

A basic gateway configuration defines upstream backend services and "mounts" them on local API endpoints:

couper.hcl:

server {
  api {
    endpoint "/example/**" {
      proxy {
        backend {
          origin = "https://httpbin.org"
          path = "/**"
        }
      }
    }
  }
}

Routing

So what happens when you request localhost:8080/example?

The api block is implicitly mounted on / on the exposed server (if no base_path is given). Therefore /example is matched against the defined endpoint configurations. We only have one here, that uses the "catch-all" operator /**. This means that our endpoint handles /example (yes, without the trailing /), /example/ and every possible sub-path of it, such as /example/user/login.

The endpoint defines a backend to proxy requests to. The only mandatory information is the origin attribute: Where should Couper connect to? This could be a local application (e.g. running in the same Kubernetes namespace), or some remote service. We can define a lot of HTTP related settings here.

Path Mapping

We have decided to mount httpbin.org onto the /example path. But the origin doesn't know about that path. Its endpoints live under / (e.g. /headers). We need to remove our local path prefix and adapt it to the backend base prefix.

The path property does just that. Everything that was matched by the /** operator of our endpoint is added to the new path where we use the operator again. /example/anything becomes https://httpbin.org/anything in the backend request.

Try it out

Start a Couper container and play with the httpbin endpoints:

$ curl 'localhost:8080/example/anything?a=b'
{
  "args": {
    "a": "b"
  }, 
  "data": "", 
  "files": {}, 
  "form": {}, 
  "headers": {
    "Accept": "*/*", 
    "Accept-Encoding": "gzip", 
    "Host": "httpbin.org", 
    "User-Agent": "curl/7.64.1", 
    "X-Amzn-Trace-Id": "Root=1-5f4b851f-23dfa24d1f3fd4cf142a7fe3"
  }, 
  "json": null, 
  "method": "GET", 
  "url": "https://httpbin.org/anything?a=b"
}

Note how host and path in the curl command line differ from the url in the response JSON.