Configuration Settings

Filters, handlers, and other objects whose configuration settings are defined by strings, integers, or booleans, can alternatively be defined by expressions that match the expected type.

Expressions can retrieve the values for configuration settings from system properties or environment variables. When IG starts up or when a route is reloaded, the expressions are evaluated. If you change the value of a system property or environment variable and then restart IG or reload the route, the configuration settings are updated with the new values.

If a configuration setting is required and the expression returns null, an error occurs when IG starts up or when the route is reloaded. If the configuration setting is optional, there is no error.

In the following example, "timer" is defined by an expression that recovers the environment variable "ENABLE_TIMER" and transforms it into a boolean. Similarly, "numberOfRequests" is defined by an expression that recovers the system property "requestsPerSecond" and transforms it into an integer:

{
  "name": "throttle-simple-expressions1",
  "timer": "${bool(env['ENABLE_TIMER'])}",
  "baseURI": "http://app.example.com:8081",
  "condition": "${matches(request.uri.path, '^/home/throttle-simple-expressions1')}",
  "handler": {
    "type": "Chain",
    "config": {
      "filters": [
        {
          "type": "ThrottlingFilter",
          "name": "ThrottlingFilter-1",
          "config": {
            "requestGroupingPolicy": "",
            "rate": {
              "numberOfRequests": "${integer(system['requestsPerSecond'])}",
              "duration": "10 s"
            }
          }
        }
      ],
      "handler": "ReverseProxyHandler"
    }
  }
}

If "requestsPerSecond"=6 and "ENABLE_TIMER"=true, after the expressions are evaluated IG views the example route as follows:

{
  "name": "throttle-simple-expressions2",
  "timer": true,
  "baseURI": "http://app.example.com:8081",
  "condition": "${matches(request.uri.path, '^/home/throttle-simple-expressions2')}",
  "handler": {
    "type": "Chain",
    "config": {
      "filters": [
        {
          "type": "ThrottlingFilter",
          "name": "ThrottlingFilter-1",
          "config": {
            "requestGroupingPolicy": "",
            "rate": {
              "numberOfRequests": 6,
              "duration": "10 s"
            }
          }
        }
      ],
      "handler": "ReverseProxyHandler"
    }
  }
}

For information about expressions, see "Expressions".