Externalize API Gateway instance configuration

When API Gateway configuration is deployed to a group, the configuration package settings are applied to all API Gateway instances in the group. You can also specify API Gateway configuration values on a per-API Gateway instance basis using environment variables in the envSettings.props file. For example, you can specify different values for the port on which the API Gateway listens for HTTP traffic, depending on the environment in which the API Gateway is deployed.

The environment variable settings in the envSettings.props file are external to the API Gateway core configuration. The API Gateway runtime settings are determined by a combination of external environment variable settings and core configuration. This mechanism provides a simple and powerful approach to configuring specific API Gateway instances in the context of API Gateway group configuration defined in policy and environment packages.

Note   Environment variables in the envSettings.props file apply to the API Gateway instance only. Configuration packages (.fed, .pol, and .env files) apply to the API Gateway group.

The envSettings.props file is located in the conf directory of your API Gateway installation, and is read each time the API Gateway starts up. Environment variable values specified in the envSettings.props file are displayed as environment variable selectors in the Policy Studio (for example, ${env.PORT.TRAFFIC}). For more details on selectors, see the API Gateway Policy Developer Guide.

Configure environment variables

The envSettings.props file enables you to externalize configuration values and set them on a per-server environment basis. This section shows the configuration syntax used, and shows some example values in this file.

Environment variable syntax

If the API Gateway configuration contains a selector with a format of ${env.X}, where X is any string (for example, MyCustomSetting), the envSettings.props file must contain an equivalent name-value pair with the following format:


When the API Gateway starts up, every occurrence of the ${env.MyCustomSetting} selector is expanded to the value of MyCustomValue. For example, by default, the HTTP port in the server configuration is set to ${env.PORT.TRAFFIC}. Specifying a name-value pair of env.PORT.TRAFFIC=8080 in the envSettings.props file results in the server opening up port 8080 at startup.

Example settings

The following simple example shows some environment variables set in the envSettings.props file:

# default port API Gateway listens on for HTTP traffic
# default port API Gateway listens on for management & configuration HTTP traffic
# path to sample directory in API Gateway instance directory

The following example shows the corresponding ${env.PORT.TRAFFIC} selector displayed in the Configure HTTP Interface dialog. At runtime, this is expanded to the value of the env.PORT.TRAFFIC environment variable specified in the envSettings.props file:

Environment variable in Policy Studio

Note   All entries in the envSettings.props file use the env. prefix, and the corresponding selectors specified in Policy Studio use the ${env.*} syntax. If you update the envSettings.props file, you must restart or deploy the API Gateway for updates to be applied to the currently running API Gateway configuration.

Related Links