Can we safely say that if ESB provides Orchestration features, it is eligible to be an implementation of BPM?
I understand that BPM has a different purpose, which is to Model some business processes and the implementation of those business processes can be done by any simple Java/J2EE application, complex SOA application, or some application saying that I provide BPM. Is that right?
First Question:
Your statement is valid for some business processes which merely models request-response interaction.
But when it comes to complex business processes we need to consider some other features apart from orchestration features. Here I have list down few such scenarios.
Let's take a business process which requires to maintain its state for a long period of time. We normally call them state-ful or long running business processes. To support these sort of business processes, there should be a state persistence mechanism. This functionality is not relevant to orchestration features.
Consider a business process, which requires some compensation capabilities. In that case, some of the business process modelling standards like, WS-BPEL have defined its compensation mechanisms. So apart from orchestration features, there are some other features which are needed to be considered.
Second Question:
Yes. But there are several pros in a BPM engine compared to your mentioned implementation mechanisms.
One advantage is, it's not possible to achieve a level of modelling abstraction provided by a BPM engine from a Java application. Let's say we used a JAVA application to implement a business process logic and that business process went to production. Say we need to change a endpoint URL of its partner service. In this case, now the business process implementation need to be modified, re-compiled and deployed back into the production system. if we implement the business process with a business process language standard like WS-BPEL, we can change the business process configuration very easily and push it back to the production. This improves the efficiency and reduce the business maintenance cost.
As well there are other reasons like easy adaptability and flexibility.
I've created these slides some time ago to explains exactly how you can use them both and the relationships between them:
http://www.slideshare.net/salaboy/jbpm5-community-training-module-25-bpm-for-developers
You need to understand the different perspective between something like BPEL/ESB/Orchestration and BPMN (business oriented) they have very different scopes.
Cheers
Normally ESB is assigned to the middle layer — orchestrating low-level services into larger service units, which will be exposed to the business for use in processes — and BPMs in the top layer.
So BPM will be used in the Business Process Orchestration Layer and ESB will enable and facilitate this by working in the Business Services and Service Enablement.
In another words to be successful with business processes first you need to have all your systems and apps exposed as services; that is where an ESB comes into play.
You could see this link : http://blogs.mulesoft.org/why-bpm-and-esb-need-to-work-together/
Let me add clarity by making the distinction between BPM, Orchestration, and ESB, via design patterns and specifications.
Generally speaking, "Orchestration" has been defined as a compound pattern employing the Process Abstraction, Process Centralization, and the State Repository design patterns. By virtue of the implementation of the State Repository Pattern and contrary to a previous post, Orchestration supports long running, synchronous business processes, just like BPM.
The major practical distinction between the 2 is that Orchestration middleware (e.g. WebSphere Process Server, BizTalk, Oracle BPEL Manager, and Windows Workflow Foundation) supports most of the WS * specifications. This includes Ws BPEL, Ws Security, Ws Atomic Transaction, Ws Business Activity, Ws Reliable Messaging, etc., while most BPM Tools do not.
As a result, feel free to use Orchestration at an Enterprise Level, but be very careful about using BPM in that scope.
In practice, both BPM and Orchestration tools enable the graphical representation of a business process. The distinction is that Orchestration may be expressed through Vendor-Neutral BPEL (Business Process Execution Language), while BPM is expressed via Vendor Specific BPMN (Business Process Modeling Notation). This is another reason to avoid BPM tools at the SOA/Enterprise Level.
In cases where a BPM Tool implements the Ws * specifications, it is an Orchestration Engine for all practical purposes. The distinction again being that BPM tools rely on Vendor-Specific BPMN and Orchestration tools rely on Vendor-Neutral BPEL.
In cases where both BPM and Orchestration need to coexist, limit BPM to application architecture (e.g. MVC style) and let Orchestration promote the sharing of enterprise assets.
An ESB is an entirely different animal. It should used for asynchronous, rather than synchronous processes and relies on a different set of design patterns (i.e. Service Broker, Asynchronous Queuing, Intermediate Routing, and the Content Enricher patterns)
Related
Is it advicible to build the MSA based services on Oracle SOA or any other ESB suite for that matter? Is there any advantage or disadvantage?
If I am using Java, Spring and JPA over a message queue - say - RabbitMQ, I can achieve it in a more controlled environment with less recurring expenses. Of course will end up mixing tools like Drools or JBPM or similar to achieve things that may be OOTB (Out of the box) in the SOA Or ESB Suite. But scaling a specific service without paying licence fee for an additional environment should certainly be a good catch right?
Microservices architecture pattern applies to development of backend systems/services, whereas ESB (e.g. Oracle SOA Suite) is intended as an intermediary layer between consumers and backend services. Backend services contain rich application logic, whereas ESB services provide only intermediary functions like routing, transformation, orchestration etc.
ESB is not intended for rich application logic, though it's possible to do that.
Using ESB (e.g. Oracle SOA Suite) to host microservices is achievable, but you will get a big overhead comparing to limited functions and scalability. If you are looking for centralized API management (tracing, security etc.), you can put an API gateway into your architecture instead of full scale ESB.
they have many common features. but how the difference?
MOM allow asynchronous while SOA does not, this is the only difference?
SOA, Service Oriented Architecture, is an architecture that defines how to structure access to business information between different applications. In a nutshell, usually, one application needs something done with a piece of information (may it be an orderfile or anything else) that application has a need. Another application may be able to do the corresponding processing of that piece of information, hence it has a capability. The first application then Consumes the Service of the second application, which Provides the Service (no matter the underlying technology, which can be anything such as JMS, HTTP/SOAP, HTTP/REST, EMail, FTP, etc.). To make this work, a Contract between the first application and the Service has to be defined which clears such things out as Message Format (XSD or similar), Protocol (HTTP/SOAP? JMS?) etc.
MOM, Message Oriented Middleware, on the other hand is just a family of software/middleware platforms. They are actual implementations, and not a high-level concept like SOA. They can be used to implement a SOA architecture, an Event Driven architecture or other architectures. Usually, MOM enriches a set of applications with asynchronous messaging where a MOM server stores and forwards the messages. Often things such as transactions, guranteed delivery, fail-over, loose coupling and load balancing are built into MOM implementations. Examples of MOM are IBM WebSphere MQ, Apache ActiveMQ, RabbitMQ, JBoss HornetQ, etc.
Message oriented middleware (MOM) is a type of technology where as SOA is a type of architecture. Even though a lot of people think about web-service when they talk about SOA, you can use MOM to implement it as well (in fact in many cases that's the better option)
What are the differences between service orchestration and service choreography from an intra-organization point of view.
Basic technologies (such as XML, SOAP, WSDL) provide means to describe, locate, and invoke services as an entity in its own right. However, these technologies do not give a rich behavioral detail about the role of the service in more complex collaboration. This collaboration includes a sequence of activities and relationships between activities, which build the business process. There are two ways to build this process: service orchestration and service choreography.
Service orchestration
Service orchestration represents a single centralized executable business process (the orchestrator) that coordinates the interaction among different services. The orchestrator is responsible for invoking and combining the services.
The relationship between all the participating services are described by a single endpoint (i.e., the composite service). The orchestration includes the management of transactions between individual services. Orchestration employs a centralized approach for service composition.
Service Choreography
Service choreography is a global description of the participating services, which is defined by exchange of messages, rules of interaction and agreements between two or more endpoints. Choreography employs a decentralized approach for service composition.
The choreography describes the interactions between multiple services, where as orchestration represents control from one party's perspective. This means that a choreography differs from an orchestration with respect to where the logic that controls the interactions between the services involved should reside.
Service orchestration: you put together several services by a fixed logic. This logic is described at a single place. You can imagine a team of people with a manager doing micro-management. The manager precisly tells what, when and who should do. The team members do not care of the entire goal of the job, the manager combines the outputs into a single deliverable.
A practical example is a BPEL process. BPEL process contains the logic, can invoke several services and combine their responses into a single service response.
Service choreography: the decision logic is distributed, with no centralized point. You can imagine a home, where everybody aims for the common good and works pro-actively without micro-management. Or you can imagine a human body, where different members are interdependent and work for the common goal.
A practical example is event driven processing, where an agent is activated by an event and does its job. All the agents make a system together. There is no centralized logic.
Choreography possibilities may go farther beyond orchestration as it is more aligned with the real world.
My opinion is that we do not need to distinguish much between these two, as we need to focus on the business logic. Where a single point of logic does the job, we do orchestration. Where a problem cannot be covered by a centralized logic, we are forced to choreography anyway. That is why we often come accross orchestration in IT, whereas choreograhy remains more an academical concept and a subject for research. And very often we do choreography without actualy knowing it, as in the real world.
Since the thread is old but still writing to it for those who will stumbled here in search of this question as I did. This is much debated question in Service-oriented architecture (SOA) which needs much cleaner explanation for beginners.
Orchestration: Executable Process
Used in private business processes
A central process (which can be another Web service) takes control of
the involved Web services and coordinates the execution of different
operations on the Web services involved in the operation
The involved Web services do not "know" (and do not need to know)
that they are involved in a composition process and that they are
taking part in a higher-level business process.
Only the central coordinator of the orchestration is aware of this
goal, so the orchestration is centralized with explicit definitions
of operations and the order of invocation of Web services.
Choreography: Multi-party Collaboration
Choreography, in contrast, does not rely on a central coordinator.
Rather, each Web service involved in the choreography knows exactly
when to execute its operations and with whom to interact.
Choreography is a collaborative effort focusing on the exchange of
messages in public business processes.
All participants in the choreography need to be aware of the business
process, operations to execute, messages to exchange, and the timing
of message exchanges.
Choreography vs. Orchestration
From the perspective of composing Web services to execute business
processes, orchestration is a more flexible paradigm and has the
following advantages over choreography:
The coordination of component processes is centrally managed by a
known coordinator.
Web services can be incorporated without their being aware that they
are taking part in a larger business process.
Alternative scenarios can be put in place in case faults occur.
Services can be distinguished between atomic services and services composed of other services. Such compositions are called "orchestration". Sometimes workflow, sometimes business process. For instance, BPEL is an orchestration language, but calls itself "business process execution language".
There is no requirement that services need to be hierarchically composed. That means, two services may talk to each other. The protocol running between them is called "choreography". It may be two services, but usually, there are more than two services involved. Each service in a choreography may be seen as orchestrator of the partner services. Each service taking part in a choreography may be realized as orchestration/workflow/process.
An orchestration shows the complete behavior of each service whereas the choreography combines the interface behavior descriptions of each service.
A good scientific article distinguishing choreography, interface behavior, provider behavior, and orchestration is the following one:
Dijkman, R. & Dumas, M. Service-oriented Design: A Multi-viewpoint Approach International Journal of Cooperative Information Systems, 2004, 13, 337-368
Andrei and others did a good job explaining what is orchestration and what is choreography. For the software architect choosing between these two alternatives, it is also important to compare them with respect to different qualities.
Orchestration pluses over choreography
Reliability: Orchestration platforms have built-in support for error handling and transaction management (compensating transactions). In choreography, custom-developed workflow and error handling tends to be more error-prone. Also, choreography is often event-driven and much of the processing is asynchronous. Therefore, choreography may require undo/correction events that add complexity to the solution.
Modifiability: Creating and changing process workflows and complex service compositions is easier in the visual BPM tools found in orchestration platforms. You gain in "process visibility".
Choreography pluses over orchestration
Performance: Orchestration incurs a performance overhead due to workflow script interpretation and the additional layer of the orchestration platform itself.
Cost: Choreography does not require additional middleware or language, which have associated learning curves and governance burden.
EDIT
An orchestration solution might introduce a SPOF if the orchestrator element doesn't employ a mechanism for high availability. Thanks #Deepak por pointing this out in a comment.
Orchestration is useful when you have control over all the actors in a process - when they're all in one domain of control and you can dictate the flow of activities. This is of course most often when you're specifying a business process that will be enacted inside one organisation that you have control over.
Choreography is a way of specifying how two or more parties - none of which has any control over the other parties' processes, or perhaps any visibility of those processes - can coordinate their activities and processes to share information and value. Use choreography when coordination across domains of control/visibility is required. You can think of choreography, in a simple scenario, as like a network protocol. It dictates acceptable patterns of requests and responses between parties.
Another way to look at Service Orchestration vs. Choreography:
- Service Orchestration: Around a Business Domain.
- Service Choreography: Among multiple Business Domains.
I'd say choreography is well suited internally for highly decentralized organizations. You won't need a central business process executor. This facilitates independent growth and development by each of organization sub-units.
(I subscribe to this interpretation of orchestration vs. choreography question:
http://geekexplains.blogspot.com/2008/07/ways-of-combining-web-services.html)
One can use both choreography and orchestration is the same system as we have done in our product. Various actors performing various tasks dispatched to them are choreographed by the event pub/sub system via events they generate. For example, when a prime mover carrying a container arrives at a warehouse, that event, which is subscribed by the warehouse manager app, prompts the warehouse manager to activate the resources to unload the cargo.
But when exceptions happen, such as the forklift to carry the load breaks down, that event starts an orchestration engine (a workflow processor) to orchestrate the task for various actors as per the exception handling workflow to handle the exception.
In orchestration, there is a conductor and there are instrument players. Players play according to how conductor conducts. If conductor is replaced, the harmonic expression will be different i.e. it is still the same play (service) but with a different outcome. For example, to provide a financial arrangement proposal, the orchestration service will conduct by asking (invoking) each player (entity or utility service, e.g. credit check) to play (return results or adjust/update its playing) according to conductor's template (business rules).
In choreography, there is a choreographer and there are groups of dancers. Choreography is a direction, but each group of dancers is autonomous in how to realize that direction.
Both orchestration and choreography are two philosophies of process formalism at large scale, i.e. collaboration spaces. A collaboration space is a formal representation for an industry, for example health industry, food industry, automotive industry or ... . So you should have some service providers at small scale able to speak some language of communication before you decide to orchestrate them or use choreography to supply some demand meaningful to end-consumer.
Orchestration typically follows what has been famous as middleware in distributed systems. Some good tooling examples within IT industry can be Juju, Zapier IFTTT. You have centralized control, auditory, modification and trouble shooting over services you consume.
Choreography is more decentralized than orchestration in the sense that it accepts more autonomous collaborators. For example bitcoin network is a collection of service providers called nodes which collectively provide a Defi service namely distributed ledger functionality to its service end-consumers. But this does not have any centralized authority in charge, and there is no total-view over whole network. There is just a consensus machanism that if respected candidate service provider joins the network and participate in end-consumer service provision. Anywhere you need to attack trusted third party and its side effects such as corruption, an orchestration would not suffice.
Again any collaboration among actors in any industry can be subjected to orchestration or choreography, so I hope limiting examples only to IT industry is not misleading.
Also I can add, naming suggests analogy between the two and stage performance. In an orchestra, every instrument player is harmonized with other team members if he/she follows the single conductor. On the other hand analogous to stage dancing in choreography there is no conductor, each stage dancer only harmonize himself/herself with his/her partner (better if spoke as peer), with no single point of harmonization leadership. But still both present harmonization to viewers.
I am looking into architectural patterns, Enterprise Services Bus (ESB) precisely. Upon reading this article Enterprise Integration, and with little to no experience I am wondering if BizTalk has is a ESB or is it just a EAI (Hub/Spokes or Bus)?
I found this NServiceBus and Biztalk, describing BizTalk as a central message broker.
Taking other ESB frameworks into account (NServiceBus and Rhino Service Bus). These frameworks have no central point to process messages.
Is Biztalk a EAI rather than an ESB?
Many thanks
BizTalk is punted by Microsoft as having ESB capabilities - see the BTS ESB toolkit
However, the term 'ESB' covers a very broad field, and there is a lot of subjectivity about an exact definition of an ESB. IMHO there are weak points in BizTalk's claim to be comprehensive as an ESB (in a > 2010 definition of the term).
BTS originated in the Hub-and-Spoke EAI era, before ESB became widespread.
BTS is more suited toward asynchronous processes than synchronous processes - latencies will vary depending on load on the system, throttling state, etc.
BTS is cumbersome when it comes to ease of versioning of services and schemas (new deployment is needed)
BTS is cumbersome when it comes to management of MANY services (e.g. Using BizTalk as a facade for all 5000 of your corporate SOA / Web Services will be painful)
FWIW we have found BTS a good fit for:
all of our synchronous and asynchronous EAI (i.e. formalized integration contracts between major LOB systems, and with trading partners), and the large number of adapters assists with integrating a wide number of protocols.
For Business Process and Business Monitoring capabilities
Addressing transactional and delivery reliablity - Biztalk has capability to retry, tracking and resumption of Suspended messages, which is useful over unreliable networks or when it comes to integration with unreliable systems.
Update, with some further comparative experiences
BTS is very centralised - ultimately, even a multi-server BizTalk cluster / group is dependent on Sql-Server. Queue based ESB products tend to be more decentralised (logically and physically), so loss of a few endpoint or queue servers should not pull the whole enterprise down.
Many queue based ESB's are built on open source technologies, with an eye on avoiding single vendor lock-in
Many contemporary ESB's seem to take a commodity-computing approach to scale out. Scaling out with products like BizTalk can become expensive.
On the plus side, the monitoring and administration capabilities of commercial offerings like BTS should not be underestimated - make sure any ESB you are considering has adequate auditing, instrumenting, retry, and diagnostic (WMI / SNMP / SCOM etc) capabilities - you'll need a dashboard to monitor the health of your bus, and there is nothing worse than not knowing where a message went. Here, centralisation administration and diagnosis is a plus.
BizTalk is a messaging and workflow orchestration platform, on which you can build ESB behaviours and capabilities. To make this easier, and standardise ESB implementation on BizTalk, Microsoft released the BizTalk ESB Toolkit - a set of guidelines, patterns and code.
The concepts of EAI and BPM have been around for a while, so there are many companies that have leveraged BizTalk to create solutions to these problems. Companies that host a full ESB on BizTalk server are far fewer, and adoption has certainly slowed in the advent of WCF/WF/NServiceBus and, of course, Azure Service Bus.
So in summary, BizTalk out of the box is nether EAI or ESB, but can do both with a number of developers applied to the problem.
By "EAI or ESB" I'm assuming you wanted to know if BizTalk follows the Hub&Spoke or the Bus architecture.
From an architecture patterns perspective, integration solutions roughly fall under one of the two patterns-
The Hub and spoke:
This involves a centralized message broker sending out messages to various receivers, while all the senders send their messages only to this broker.
Thus neither the senders nor the receivers need to be aware of each other.
This is typically what many people refer to as EAI (although it is absolutely possible to implement an EAI solution that follows the BUS pattern).
Solutions following this pattern are easy to develop and administer. All the routing logic is centrally managed at one place - in the hub.
But as you would have guessed, this has a glaring drawback - single point of failure. If the hub crashes everything comes to a halt. Also, this model doesn't scale very well.
BUS:
Enterprise Integration solutions developed around this pattern are generally referred to as ESB. There is no intelligent central authority here. All senders publish their messages on the bus. The receivers need to be intelligent enough to determine which messages are intended for them and take them off the bus.
Thus the senders and the receivers need only be aware of the bus. But here the routing logic is spread across the receivers so there is no single point of failure. Also this model is highly scalable. However such solutions are quite complex and difficult to administer.
Coming to the question which pattern does BizTalk follow- it is a hybrid of both these patterns.
the Hub-like appearance is very obvious with its centralized Messaging Engine, and a central MessageBox database. This gives one the simplicity and ease of administration which is typical of the hub approach.
But if you look at the BizTalk architecture, one can have a Host with its Host Instances spread across multiple servers. It is also possible to have the different BizTalk databases like MessageBox, Tracking, Ent SSO etc. configured on different servers. This makes BizTalk solutions more scalable and tolerant to faults than the run-of-the-mill hub implementations - which is a behavior usually attributed to the bus approach.
Hope this answers your question.
BizTalk is certainly an ESB. EAI is more of a loose concept - BizTalk can certainly be deployed to support EAI, and it can also do a lot more.
BizTalk is more than an ESB but certainly fits the bill. This link is a little old, but answers your exact question.
EDIT: Here is a more-recent MS link that gets into specifics of implementation.
BizTalk can be used as both EAI and ESB.
As for ESB, the BizTalk server architecture is publish-subscribed, a single message can be published to the messagebox which acts as the messaging backbone bus. That message can be received by one or more destination systems that are subscribed to that message. Of course there more capabilities and features that you can get by using BizTalk server like the mapper tool and the use of pipeline components for example.
For use as EAI, BizTalk offers you orchestrations that manage the business logic, LOB(Line of business) adatpers to connect to systems(also legacy), mapper tool, rules engine, and a lot of what you need in order to integrate the different systems in or outside your company.
Absolutely! Biztalk comes from an EIS background, which makes perfect sense for ESB as an infrastructure backplane for service-oriented architectures that span hybrid technical platforms.
At a previous company we chose Biztalk in preference to the IBM ESB product for reasons of functionality and lower cost.
It is Microsoft, so you get what you pay for, but still well worth looking into.
Biztalk Server withot "ESB Toolkit" Is not an ESB.
Because of the following:
Is a contract first, need to build you message types first.
Need to Plan the whole scenario first to minimize the impact of changes.
Changes requires Deployment which increases downtime.
Regarding to your qustion, Yes BizTalk Server is EAI Product
I agree with most of what's said here. It's a stretch to pitch BizTalk as an all inclusive EBS solution even with the EBS toolkit.
To address a couple points made here ...
•BTS is more suited toward asynchronous processes than synchronous
processes - latencies will vary depending on load on the system,
throttling state, etc.
BizTalk hosts with unchanged defaults are not ideal for a low latency. But those hosts are meant to be tuned. Out of the box configuration is not suitable for any situation where throughput is needed. In my experiences of walking into an organization where BizTalk has been shunned there is always an untuned single host setup sitting in the middle of it. It is somewhat analogous to making tables in a dbms with no indexes, getting performance issues and saying the dbms itself sucks.
•BTS is cumbersome when it comes to ease of versioning of services and
schemas (new deployment is needed)
Like with any development platform you need to have a deployment strategy. If schemas have version in the namespace you do not need to redeploy anything. A new version maybe deployed without taking anything down.
As far as the service endpoints are concerned BizTalk can host web services without the use of IIS (BizTalk can use HTTP.SYS to host just as IIS does). To host an inprocess service in BizTalk is merely a matter of importing a binding which can be done without stopping anything in BizTalk. In those end points you can implement versioning as well (like http:.../thing/v1, http:.../thing/v2, etc.).
Anyway ~5 years have passed I'm sure you have hit a conclusion before now :)
BizTalk can do both ESB and EAI, depends how you design your biztalk applications.
Is an Enterprise Service Bus (a tool that acts as a mediator, a message broker, a service enabler, schema transformation enhancer, transparent location provider, service aggregator, load balancer, monitor, and all that stuff) responsible to orchestrate services?
What about putting an automated business business process with more than thousand steps and dozens of service invocations inside your enterprise service bus?
Would you do it, or would you use a specialist in orchestration such as a BPEL engine?
Please gimme you opinion.
Yes and no. There's a thin, and sometimes indistinguishable line between orchestration and aggregation/service augmentation.
In general, if you've got any long-running or complex business process (process being the key word, although I'm going to avoid defining it) - that's best suited to BPEL.
Simple tasks, such as aggregating the results of three service calls, could and often should be done in an ESB layer.
It's not worth losing too much sleep over, though
Disclaimer: I am an IBM ESB consultant, although I'm not writing this in an official capacity.
No, an ESB's responsibility is not the orchestration of services (per se).
The ESB provides a layer of abstraction at the "software infrastructure level".
This means that an ESB is a "single logical abstract port of call for connectivity" with any service that is published on the bus.
The ESB being abstract, means that consumers of services on the bus, don't "need to know" deployment details of the service, and it is possible to expose "internally facing services" with a single document model. The ESB provides low level services (such as protocol translation and message transformation), so that internally services can communicate in a simplified fashion.
This implies some orchestration: The ESB provides orchestration of the afore mentioned low level services (e.g. when service X is called via IIOP, translate this to SOAP with Attachments. Then transform the request from whatever serialized data to an XML payload).
The orchestration you would typically avoid in an ESB is: In order to process this (insurance) sale, we first need to validate the information provided by the buyer, then we need to underwrite the risk of insuring, and finally calculate the premium that needs to be paid for the insurance, after which we need to… etc.
The steps described above are clearly a business process (which could even be interrupted… e.g. if automatic underwriting is not possible, then a human underwriter needs to further assess the risk).
Business Services (e.g. Validation, Underwriting, Premium Calculation) that make up a Business Process (e.g. Insurance Sale), which is what is typically referred to as Orchestration, is best suited to happen in a Business Process Engine and defined using a formalized Business Process Modeling Language (such as BPEL).
Also making a guess about the many steps in your process: In the above example, Validation is a (course grained) service. The validation rules themselves are internal to that service. For complex business rules (i.e. not business process), the use of a Business Rules Engine may be required.
My short quick answer is NO, that not its responsability.
I would rather let that to the BPEL or a BPM suite.
Mhh I don't know what else to add :) ... Good luck?
Now my own vision.
Regarding all the work an ESB has to do, putting service orchestration inside the main infrastructure element of your SOA is not a good idea.
Aggregate, ok! But keeping your communication channel busy with business logic will, for sure, cause a terrible impact in the ability to delivery other features.
After all, most ESBs such as as BEA Aqualogic Service have a limited support for orchestration including lack of stateful capabilities, and activities like wait (a timer) or pick (wait for some input to move on the process), split/join capabilities (already added on ALSB 3.0), and so on.
No way. Just use tools like a BPEL engine or a tool like Weblogic Integration.
Thanks.
Whenever you have two or more services that interact use service orchestrator, i.e. for composition and process control services. If you have esb expose this composition service on esb. Now if you have to compose new service that includes this composition service use orchestrator and again expose on esb.
Use esb as service delivery mechanism and web service broker and proxy. In composing a service orchestrator will use esb to reach interacting services. If these interacting services use incompatible xml schemas esb can transform/map them to common schema in runtime and route service requests based on the content, e.g. namespace.
Yes orchestration is a responsibility, in most cases, of the ESB. Or, alternatively, if you draw a line between ESB infra and orchestration infra, then you are doing so on a physical level for performance reasons, not for logical attribution of responsibility.
You have 2 choices - when, for example, an HR system receives a new employee - where do you place the business logic that says "the compliance department will need to approve and check first, and then if that's ok, the HR department will need to finalise the hire, then the accounting department will need a new entry, and then the payroll system will need updating, and if that fails, then we'll need to send an email to HR"? If all business processes are considered 'owned' by the initiating dept/application, then the overall system that is the enterprise becomes complex, with disparate orchestration systems.
The second choice is centralise the orchestration, essentially making it a logical partner of the messaging platform. If you choose to see these as separate artifacts, that is up to you, but it is equally valid to described both as ESB.
An Enterprise Service Bus should never be responsible for orchestrating services.
Orchestration implies a minimum of "smarts", specifically the ability to compensate for failed transactions. Service bus tools will often say they offer "try-catch" or something like that but the ability to run scoped componsation is the mark of a proper orchestration tool. Additionally the ability to wait, know its own state, or keep things in suspense is another indicator that you're dealing with an orchestrator and not a bus.
Speaking to 1000+ steps plus dozens of services, consider the if-then's in the process. If all the if-then statements in your 1000 steps speak only to routing with no change to the payloads then you're still in "routing" and therefore still in ESB. But if there's even one nested if-then and I start to look for different tools. Aside, if-thens that look like routing can very quickly impact business logic. Once business logic starts showing up then a better language such as BPEL or BPMN is better.
The example of an orchestra conductor is often given to describe how orchestration works, a central individual directing the musicians according to a score. Often what's left off is the idea that the conductor is not only directing, but listening as well, and if something goes wrong can compensate in a reliable, repeatable way.
For instance imagine our first conductor goes to bring in the tuba player but said tuba player has decided to go do something else. A simple pinball-style "orchestrator" will bring in the tuba section, knowing full well it isn't there, and then wait for the audience to complain later. A really savvy conductor would see the tuba gone, and immediately bring up the deeper baritone horns to compensate.