API Gateways with Dedicated Backends

We can extend the multiple gateway environments feature by utilizing dynamic endpoint capabilities of WSO2 API Manager to have each gateway point to a different back-end endpoint. API Gateway is the actual runtime of the APIs that are developed and published from the API Publisher. WSO2 API Manager is capable of publishing APIs to different Gateways where API users connect to those API Gateways in order to do the actual API calls through the applications to which they are subscribed. 

However, the API Publisher can only provide a single static endpoint for an API in the implementation. Therefore, the API call is directed to a single endpoint in whichever Gateway the API is deployed in, as depicted in the diagram below.

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However, in most situations, you would want to have each Gateway proxying to a dedicated backend API. To provide that capability, WSO2 API Manager provides the ability to specify dynamic endpoint URLs at the time of specifying the API endpoint URL. This UEL is resolved at runtime with the details (host and port) specified at the startup of each Gateway. Each gateway then points to a dedicated backend API, as depicted in the digram below.

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Configuring dynamic endpoints

Follow the steps below to configure a dynamic endpoint as the API endpoint.

1. Start the WSO2 API Manager server that includes the API Publisher component and create an API.

2. Go to the Implement tab of the API and replace the host and port of the API endpoint with {uri.var.host} and {uri.var.port} respectively, as shown below.

3. Save and publish the API. 

4. Navigate to the <API-M_HOME>/repository/deployment/server/synapse-configs/default/sequences directory of each Gateway and create the following sequence.

   <sequence xmlns="http://ws.apache.org/ns/synapse" name="WSO2AM--Ext--In"> <property name="uri.var.host" expression="get-property('system','host')" /> <property name="uri.var.port" expression="get-property('system','port')" /> </sequence>

5. Execute the following command when starting up each Gateway to set the system variables at the server start up from within the <API-M_HOME>/bin directory by replacing the following values.

   ./wso2server.sh -Dhost=<ip_of_backend_environment> -Dport=<port_of_backend_environment>

   Now the Gateways have started with the dedicated backend host/port combinations.

6. Invoke the API.

You receive the response from the API, which is sent through the dedicated backend, from the Gateway that this API is published.