Choosing Between Route, Service Callout and Publish

When you are first starting with OSB it can be a little tricky to determine when to use a Route, Service Callout or a Publish node.  All three can be used to call either a Business service or a local Proxy service.  You can use the following lists to determine which will best fit your needs.

Route

1. Last node in request processing.  It can be thought of as a bridge between request pipeline processing and the response pipeline processing.
2. You can only execute one route in your Proxy Service.
3. Can only be created in a route node.
4. OSB will wait for the Route call to finish before continuing to process.
   1. If you are calling a Business service and you specify Best Effort for QoS (Quality of Service), then OSB will release the thread it is holding while the business service executes.
   2. If you are calling a Business service and you specify Exactly Once or At Least Once for QoS, then OSB will hold onto the thread while the business service executes.
   3. If you are calling a local Proxy service, then OSB will hold onto the thread until the Proxy service finishes executing.

Service Callout

1. Can have multiple Service Callout nodes in a Proxy service.
2. Pipeline processing will continue after a Service Callout.
3. Can be invoked from the request and/or response pipelines.
4. Used to enrich the incoming request or outgoing response. For example, a call to get a country code.
5. Used for real time request/response calls (Synchronous calls).
6. OSB will hold a thread and not continue until the Service Callout completes.
7. Can tie up resources and degrade performance under heavy loads.

Publish

1. Can be synchronous or asynchronous
   1. If you are calling a business service with a Quality of Service of Best Effort , then it will be an asynchronous call.
   2. If you call a business service with a Quality of Service of Exactly Once or At Least Once, OSB will wait until the processing completes in the business service completes before proceeding and it is effectively a synchronous call.
   3. If you are calling a local proxy service, OSB will wait until the processing in the local proxy service completes and it is effectively a synchronous call.
2. Can be invoked from the request and/or response pipelines.
3. Best to use when you do not need to wait for a response from the process you are calling (Fire and Forget.... Asynchronous Calls)

For more detailed information on the differences between a Route and a Service Callout including how OSB handles threads during each of these calls see OSB, Service Callouts and OQL - Part 1.