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Backend Configuration

A backend block defines the connection to a local/remote backend service.

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

The connection can be modified via transport settings like max_connections, timeout, disable_certificate_validation etc. You can find the complete list of the transport settings here.

For example, if a backend should to be relieved, you can limit the number of simultaneous connections (in any state - active or idle) to the backend service via max_connections and limit the total request duration via the timeout setting:

server {
  endpoint "/**" {
    proxy {
      backend {
        origin = "https://httpbin.org"
        path = "/**"
        max_connections = 10
        timeout = "5s"
      }
    }
  }
}

Reusing backend configurations

You can "reuse" backend configurations by defining a labeled backend in the definitions block:

definitions {
  backend "main" {
    origin = "https://httpbin.org"
    timeout = "5s"
    max_connections = 10
    ttfb_timeout = "10s"
  }
}

and then refer to it from an endpoint:

  endpoint "/anything" {
    proxy {
      backend = "main"
    }
  }

When you start Couper and send a request to the endpoint /anything, you will get a response from https://httpbin.org/anything:

$ curl -is localhost:8080/anything
HTTP/1.1 200 OK
Access-Control-Allow-Credentials: true
Access-Control-Allow-Origin: *
Connection: close
Content-Type: application/json
Date: Wed, 19 May 2021 10:41:13 GMT
Server: couper.io
Vary: Accept-Encoding
Content-Length: 343

{
...

  "url": "https://httpbin.org/anything"
}

You also have the option to refine this reference, depending on the use case in the respective endpoint block:

  endpoint "/downloads/**" {
    proxy {
      backend "main" {
        path = "/anything/**"
        timeout = "10m"

        set_request_headers = {
          x-hello = "from Couper"
        }
      }
    }
  }

In this example we increase the request timeout for all /download/** routes to 10m and add a HTTP request header field X-Hello: from Couper.

The other settings (max_connections, ttfb_timeout etc.) are inherited from the backend configuration in the definitions block.

When you request the endpoint /downloads, you will see the additional header:

$ curl -is localhost:8080/downloads
HTTP/1.1 200 OK
Access-Control-Allow-Credentials: true
Access-Control-Allow-Origin: *
Connection: close
Content-Type: application/json
Date: Wed, 19 May 2021 10:46:48 GMT
Server: couper.io
Vary: Accept-Encoding
Content-Length: 374

...

  "headers": {
    ...

   "X-Hello": "from Couper"

...

  "url": "https://httpbin.org/anything"
}

See also