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Router Expressions Language Reference for Kong Gateway

With the release of version 3.0, Kong Gateway now ships with a new router. The new router can describe routes using a domain-specific language called Expressions. Expressions can describe routes or paths as combinations of logical operations called “predicates”. This document serves as a reference for all of the available operators and fields. If you want to learn how to configure routes using Expressions read How to configure routes using Expressions.

General design

Kong router Expressions are designed as combinations of simple comparisons called “predicates”. All predicates have one of the following form:

field op value
transformation(field) op value

Example:

http.path ^= "/prefix/"
lower(http.path) ^= "/prefix/"

Note: transformations only works on fields, it will not work on the value side of the predicate. This means you can not write:

http.path ^= lower("/preFIX/")

Predicates can be grouped with parenthesis () or logical operators ||, &&:

Example:

(http.path ^= "/prefix/" && net.port == 80) || http.method == "POST"

Types

Router expressions are strongly typed. The operators available to each field depends on the type of that field. For example, you can not perform string comparisons on a integer type field.

Available fields

String

String transformations

Integer

IP

Boolean

More information

• Expressions repository
• How to configure routes using Expressions