Routing 2-way Synchronous response to endpoints other than the initiator
Recently, in our implementation of an ESB 2.0 BizTalk 2009 solution, a requirement popped up where an endpoint initiates a request to a synchronous system, and the system responds back with a response. In typical development practices, this is referred to a request/response or client/server pattern. You may say to yourself, “big deal, this is easy…” In a normal solution, the response is routed back to the initiator of the request. Lo and behold, we came across a scenario, where the response needs to be routed to other endpoints based on fairly complex rules and processes; not the original caller (initiator), hence the purpose of this blog entry.
As a BizTalk Developer, you say the above is not a problem. Why? Because BizTalk can handle designs like this with ease, using orchestrations, static send ports with unique filter expressions, and even orchestrations with dynamic send ports. You can actually put the complex logic, rules and processes inside custom components, or the Business Rules Engine (BRE) within orchestrations or even pipeline components. However if we’re staying true to the Agile game, and we want to build a architecturally sound ESB, using the normal BizTalk approach doesn’t fit the bill, in other words, it won’t work. The reasons why are simple, we either loose Agility, gain invisibility, create a mystery black box with custom code, or have increasingly complex algorithms which are prone to break and miss the agile mark altogether. The goal here is to think about BizTalk 2009 and the ESB 2.0 toolkit as a set of capabilities and then model the capabilities to generate the result you want.
Question: So now what capabilities do we need?
Answer: We want the ability to design steps or process flow which accepts a message from an initiator, and then based off of some rules, dynamically determine the 2 way service, retrieve the response and through more rules dynamically send the response to another endpoint who is not the initiator.
Question: So which capabilities match BizTalk and ESB?
Answer: The capabilities to design steps and process flows are the Itineraries pattern of ESB. The BizTalk Business Rules Engine incorporates the complex logic. The ESB Resolvers assist to resolve logic, and endpoint addresses, such as the 2 way service to invoke, and the resulting endpoint to send the responses to. In addition to the resolvers, BizTalk provides WCF Adapters to send and receive the request/response and results.
Question: So how do we do this?
Answer: You model an itinerary in BizTalk 2009′s ESB 2.0 using the Itinerary designer that accepts a message from a caller (initiator), and then sends the request to a 2-way Synchronous Endpoint, which then blocks (correlates automatically for the response) and then sends the Response to a completely different endpoint based off of a Business rule.
Question: Is this easy?
Answer: Yep Follow these high level steps:
Create an Itinerary using the ESB Itinerary Designer.
Configure the Itinerary to use a 2-way Receive Port, even though you will use a 1-way receive port in production.
Configure the Itinerary to be a Request/Response Itinerary, which is to say verify the IsRequestResponse = true. (See the Itinerary Cache Post for more info on this… http://dgoins.wordpress.com/2010/02/22/overstanding-the-esb-itinerary-cache-2/)
Model the itinerary with with the call the the synchronous request/response endpoint.
Within your steps, use the BRE Resolver to determine maps, and endpoint addresses for the configuration of which synchronous endpoint to send the request to.
Optionally: Use the Service Broker shape to route to different endpoints based off of promoted properties from the response.
Lastly, use a Business Rule Resolver to dynamically determine the resulting endpoint configurations.
Below is an example of an Itinerary which uses Business Rules to invoke a Synchronous endpoint and routes the results to another endpoint which is not the initiator.
Explanation of Itinerary:
The above image can be read following the directions of the arrows, starting with the upper Left shape named: ReceiveMsg . This first shape signifies an ESB OnRamp, which equates to a BizTalk Physical receive port.
The next shape: MapToCanonical represents an ESB Messaging Step. Messaging steps are processes or components that are destined to execute inside of pipelines. These pipelines are configured with ESB based pipeline components such as the ESB Dispathcher, which understand the Itinerary step mechanism to execute ESB Itinerary steps. In the above example, the MapToCanonical step uses a Transform based ESB Step process to execute a BizTalk transformation (Map) to convert the message received from the OnRamp into a canonical message format. The map which executes is determined by the ESB Resolver: SetMapToCanonical . This resolver utilizes the BRE Resolver to execute and evaluate complex logic using the BizTalk Business Rules Engine (BRE) to choose the correct map for transformation.
The next step: RouteToEndPoint is another ESB messaging step, which utilizes the ESB Routing process to promote properties and publish the message to the BizTalk Message box. This step is configured to use the BRE Resolver named: GetURI . This resolver executes business logic and evaluate rules to determine the URI address, and Send adapter to send the request to.
The next step: PushToMsgBox, is an off ramp extender shape which gathers more promoted property information from the actual ESB OffRamp: SendToEndPoint (BizTalk Physical Send Port). Here’s an interesting point to note, remember that the ESB Itinerary pattern is just a model to design steps as in the order of execution, not the actual process such as an orchestration. As we define our steps, BizTalk needs to know where these ordered steps should execute. In other words, when we use “Messaging Steps” these obviously execute inside Messaging components of BizTalk, hence pipelines stages. However, for BizTalk we have two sides of the messaging system. BizTalk has a messaging stack before saving to the Message Box (Receive Pipelines), and a stack after the Message Box (Send Pipeline). In the design above, the PushToMsgBox off ramp extender is used to signify all steps after this will execute in the Send Handler (Send pipeline stages).
The next step after the off ramp extender is the MapToEndPoint step. This step, again is a messaging step which uses the BRE Resolver named: SetMapToEndPoint , will be executed after the message is published to the BizTalk Message box, and inside the send pipeline associated with the send port configured through Off Ramp: SendToEndPoint .
The next step is the SendToEndPoint ESB Off Ramp. This Off Ramp is configured to use a 2-way Solicit-Response dynamic send port. From a BizTalk perspective, the 2-way dynamic send port is configured to use a send pipeline which contains the ESB Dispatcher pipeline component, and the ESB Itinerary Cache pipeline component. The receive pipeline is configured to use the ESB Itinerary Cache, Xml Disassembler, and the ESB Dispatcher components respectively. The 2-way send port is also configured with the 4 basic ESB promoted properties within the Filter expression. Screen shots of the various properties and values are provided below.
The next step is MapResponseToCanonical . Notice here that the messaging step is set to run in the Receive Handler (Receive Pipeline) of the SendToEndPoint off ramp. This means that this step runs on the receiving side of the 2-way dynamic send port. This step is configured to use the ESB Transformation service, and the BRE Resolver to again determine which map to use for transformation. This step transforms the reponse to a canonical format to eventually publish back to the Message Box.
The next step is RouteResponseToEndPoint, just like step before, this step also is configured to execute in the Receive Handler of the SendToEndPoint off ramp. Which also means it will execute on the receiving side of the 2-way dynamic send port. This step is also configured to use the ESB Routing service and again the BRE Resolver to determine the Endpoint URI and adapter to use to send the final response.
The next step is PushResponseToMsgBox. This step is an off ramp extender which signifies that the remaining steps will be executed after the message is published to the Message Box, along with any other special properties that need to be promoted.
The next step is MapResponseToEndPoint, this step is a messaging step which again uses the ESB Routing Service and the BRE Resolver to determine the Uri address and BizTalk Send adapter settings to use for sending the response.
The last step is SendResponseToEndPoint, this is the Off Ramp which points to a simple Dynamic Send port for actually sending the response from BizTalk.