Local Transport

Apache Axis2's local transport implementation is used to make fast, in-VM (Virtual Machine) service calls and transfer data within proxy services. The transport does not have a receiver implementation. The following class implements the sender API:

org.apache.axis2.transport.local.NonBlockingLocalTransportSender

WS-Security cannot be used with the local transport. Since the local is mainly used to make calls within the same VM, WS-Security is generally not required in scenarios where it is used.
If you want to make calls across tenants, you should use a non local transport even if they run from the same VM.
If you need to use local transport with callout mediator, you do not need to perform configuration mentioned in this section as callout mediator requires blocking local transport which is configured by default in WSO2 ESB distribution.

To use this transport, configure an endpoint with the local:// prefix. For example, to make an in-VM call to the HelloService, use local://services/HelloService. Note that the local transport cannot be used to send REST API calls, which require the HTTP/S transports.

Configuring the Local Transport

By default, WSO2 ESB provides CarbonLocalTransportSender and CarbonLocalTransportReceiver, which are used for internal communication among Carbon components and are not suitable for ESB service invocation. To enable the local transport for service invocation, follow these steps.

1. In the carbon.xml file at location <ESB_HOME>/repository/conf, an endpoint is available as follows by default.

<ServerURL>local://services/</ServerURL>

Replace it with

<ServerURL>https://${carbon.local.ip}:${carbon.management.port}${carbon.context}/services/</ServerURL>

2. In the axis2.xml file at location <PRODUCT_HOME>/repository/conf/axis2/axis2.xml, there is a transport sender and receiver named 'local' specified as follows in two different places:

<transportReceiver name="local" class="org.wso2.carbon.core.transports.local.CarbonLocalTransportReceiver"/>

<transportSender name="local" class="org.wso2.carbon.core.transports.local.CarbonLocalTransportSender"/>

Remove both these lines and add following line.

<transportSender name="local" class="org.apache.axis2.transport.local.NonBlockingLocalTransportSender"/>

For more information about transports, see Working with Transports.

Example

There are three proxy services in WSO2 ESB named LocalTransportProxy, SecondProxy and StockQuoteProxy. The invocation of services take place in the following order.

1. The stockquote client invokes LocalTransportProxy.
2. The message received is forwarded to SecondProxy.
3. The message is forwarded to StockQuoteProxy.
4. StockQuoteProxy invokes the backend service.
5. StockQuoteProxy receives a response.
6. The response is returned by StockQuoteProxy to SecondProxy.
7. The response is returned by SecondProxy to LocalTransportProxy.
8. The response is returned by LocalTransportProxy to the client.

When local transport is not used, the messages sent by one proxy service to another (i.e. flows b, c, f and g) goes through the network as shown in the following diagram.

Local transport can be used as shown below to prevent message flows between proxy services from going through the network. When local transport calls are in JVM calls, the time taken for communication between proxy services will be reduced since no network overhead will be introduced.

Run sample 268 for a demonstration of this scenario.