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How to Configure Routes using Expressions

Configuring routes using expressions allows for more flexibility and better performance when dealing with complex or large configurations. This how-to guide explains how to switch to the expressions router and how to configure routes with the new expressive domain specific language. Familiar yourself with the Expressions Language Reference before proceeding through the rest of this guide.

Prerequisites

Edit the kong.conf to contain the line router_flavor = expressions and restart Kong Gateway.

Note: Once you enable expressions, the match fields that traditionally exist on the route object (such as paths and methods) will no longer be configurable and you must specify Expressions in the expression field. A new field priority will be made available that allows specifying the order of evaluation of configured Expression routes.

Create routes with expressions

To create a new route object using expressions, send a POST request to the services endpoint:

curl --request POST \
  --url http://localhost:8001/services/example-service/routes \
  --form-string expression='http.path == "/mock"'

In this example, you associated a new route object with the path /mock to the existing service example-service. The Expressions DSL also allows you to create complex router match conditions:

curl --request POST \
  --url http://localhost:8001/services/example-service/routes \
  --header 'Content-Type: multipart/form-data' \
  --form-string 'expression=(http.path == "/mock" || net.protocol == "https")'

Create complex routes with expressions

You can describe complex route objects using operators within a POST request:


curl --request POST \
  --url http://localhost:8001/services/example-service/routes \
  --header 'Content-Type: multipart/form-data' \
  --form-string name=complex_object \
  --form-string 'expression=(net.protocol == "http" || net.protocol == "https") &&
                (http.method == "GET" || http.method == "POST") &&
                (http.host == "example.com" || http.host == "example.test") &&
                (http.path ^= "/mock" || http.path ^= "/mocking") &&
                http.headers.x_another_header == "example_header" && (http.headers.x_my_header == "example" || http.headers.x_my_header == "example2")'

See the expressions language overview page for common use cases and how to write expressions routes for them.

For a list of all available language features, see the expressions language reference.

Matching fields

The following table describes the available matching fields, as well as their associated type when using an expressions based router.

Field Type Available in HTTP Subsystem Available in Stream Subsystem Description
net.protocol String ✅ ✅ Protocol of the route. Roughly equivalent to the protocols field on the Route entity. Note: Configured protocols on the Route entity are always added to the top level of the generated route but additional constraints can be provided by using the net.prococol field directly inside the expression.
tls.sni String ✅ ✅ If the connection is over TLS, the server_name extention from the ClientHello packet.
http.method String ✅ ❌ The method of the incoming HTTP request. (for example, "GET" or "POST")
http.host String ✅ ❌ The Host header of the incoming HTTP request.
http.path String ✅ ❌ The normalized request path. This field value does not contain any query parameters that might exist.
http.headers.<header_name> String[] ✅ ❌ The value(s) of request header <header_name>. Note: The header name is always normalized to the underscore and lowercase form, so Foo-Bar, Foo_Bar, and fOo-BAr all become values of the http.headers.foo_bar field.
http.queries.<query_parameter_name> String[] ✅ ❌ The value(s) of query parameter <query_parameter_name>.
net.src.ip IpAddr ❌ ✅ IP address of the client.
net.src.port Int ❌ ✅ The port number used by the client to connect.
net.dst.ip IpAddr ❌ ✅ Listening IP address where Kong Gateway accepted the incoming connection.
net.dst.port Int ❌ ✅ Listening port number where Kong Gateway accepted the incoming connection.

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