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In a Rebus service bus, there is a single message transport queue per endpoint. It is possible for an endpoint to handle more than one message, and it is possible to have only a single endpoint in a system.
Other than the throughput of messages, what reasons are there to use more than a single endpoint in a Rebus service bus system?
Excellent question! :) There can be many reasons why you might want to have several Rebus endpoints active at the same time.
An obvious reason is that you might want to host the endpoints in separate processes so you can update them independently of each other. But since this reason is pretty obvious, I assume you are thinking about reasons one might want to host multiple Rebus endpoints in the same process.
Let me just mention a few(*):
Concurrency requirements
One endpoint might be hosting data that experiences contention and therefore does not benefit from being able to process messages concurrently - this endpoint will probably have only a few threads and low parallelism, possibly 1/1.
Another endpoint might be doing stream-based data processing (e.g. loading blobs from one place into another, downloading data from web services, etc.), which can be done with very high throughput and low resource requirements with one single thread and a high level of parallelism - e.g. 1/20.
Yet another endpoint might be doing a lot of serialization/deserialization, which is usually CPU-bound, and therefore might benefit from running on a many-core box with many worker threads and matching parallelism - e.g. 10/10.
As you can see, the type of tasks performed by an endpoint can call for a configuration that matches the nature of the tasks.
SLAs
One endpoint might be designated for processing low-priority background stuff, like e.g. moving data to cold storage, optimizing storage of historic data, etc.
Another endpoint might be processing messages where low latency is the most important quality attribute.
If these two were using the same queue, the low-priority background stuff could sometimes clog up the queue, hindering low-latency processing of the other messages.
Logical separation
I have many times started out by hosting several Rebus endpoints in the same process because it was easy to deal with during development, while keeping the endpoints separate because they were implementing different business functions.
This way it is easy to physically break them apart some time later on, allowing for a higher degree of separation and independence.
(*) Udi Dahan works with the concepts "business components" and "autonomous components" where the first one is an implementation of a business capability and the second one is what business components are decomposed into, mostly for technical reasons.
I guess you could say that the first two reasons I mentioned are separate endpoints for "autonomous component" reasons, whereas the third is separation because things belong to different business components.
Udi keeps a pretty strict view of these concepts that is completely orthogonal to how the system is physically composed, but I almost always end up with pretty high convergence between logical separation and physical separation.
I'm dealing with an architecture approach that doesn't convince me deeply, but I can't figure out a good alternative.
Basically our company is pretty much always under attack... I mean there's constant attempt of phishing, spoofing, bruteforcing, etc. attacks to our public web site.
Decision has been taken to delpoy the web apps on a 3 tier configuration (I really mean tier, not layer as often they're confused), letting the presentation tier being on a machine, in a subnet exposed to the internet, and the rest of the application being on an internal subnet, with an application server that basically expose everything needed by the presentation server or other internal system, and obvioulsy a database server.
Now, the separation between presentation and business logic, is very heavy both in terms of development and in terms of performance: use a DLL dedicated to perform data access is obviuosly faster than call a remote service to perform the same operation.
This, on the other, has been seen as the most pratical way to improve security: in this deployment model the presentation layer could be break throug by some hacker, but still, from there, they gain no access to the database, and that's the important part.
The communication between the presentation tier and the business tier is made through WCF services, exposing authenticated SOAP methods.
Moreover the approach is to let all the business logic in the BL tier, letting the presentation tier be quite "stupid": so the BL tier is not merely a secured DAL layer, but contains all the logic.
Is that an acceptable approach? There's some smarter way to handle such scenario out there, that we're missing? Would you prefer to keep BL on the presentiation tier, living just the DAL in the middle tier? And for what reason?
I'm feeling pretty unsure about our solution, so I'm asking for any advice.
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.
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.
I'm working on a .net portal which would be having lots of concurrent users.
so scalability,performance need to be addressed in the design and architecture.
We plan to use load balancing in the application.
Keeping this in mind,what would be the best way of communicating between IIS web server(hosting aspx,aspx.cs files) and application server (hosting .net assemblies like business logic and data access layer)?
Should it be .net remoting or soap web service?or is there any other approach?
Thanks.
Is there another approach? Yes - don't distribute your objects.
The most scalable approach is to NOT to distribute your objects away from each other. Ask yourself, why do you want to deploy one flavor of code to an "app server" while another flavor of code goes to a "web server"? The communication that goes on between those two layers, if they are distributed, will be much much much much (etc etc) more expensive than a local call.
With today's 64-bit servers, with all of that memory, and the hot CPUs, and with ASP.NET's superior memory management, why not put your business logic and DAL on the same physical machine as the ASPX files? Why not?
If you need to scale, add more servers. Simple.
There are good reasons, of course, to distribute. The most common good reasons have to do with domains of ownership - along several axes: security management, or even budget and control. In other words, to take the latter case, if team is responsible for running the business logic and a separate team is responsible for building and running the web layer -then it may make sense to distribute those two things to allow independence of management. Most of the good reasons for distributing computer code, have their origins in the structures of the human organizations using or developing the code.
There is no good technical reason why a web page should not run on the same CPU, sharing the same CLR VM and memory heap, as the database access layer.
Regardless what you do with distribution, it would be unwise to architect your system with less-than-formal interfaces defining the connections between the layers. If you keep formal interfaces, then it should be no problem for you to measure the perf and efficiency of a distributed approach versus a co-located approach.
Do you really need an app server? Just how big are you talking exactly? For example Stackoverflow.com has ~50k uniques a day and doesn't have an app server so I assume you are talking much bigger than that? Most performance bottle necks come down to database issues so I would concentrate on that.
I suggest you take a look at the Patterns and Practices groups guidelines for performance, more specifically Chapter 6 - Improving ASP.NET Performance of the guideline. I agree with Cheeso that you should seriously consider NOT physically splitting your application layer and UI layer if you can. The P&P guideline has the following notes:
Avoid Unnecessary Process Hops
Although process hops are not as expensive as machine hops, you should avoid process hops where possible. Process hops cause added overhead because they require interprocess communication (IPC) and marshaling. For example, if your solution uses Enterprise Services, use library applications where possible, unless you need to put your Enterprise Services application on a remote middle tier.
Understand the Performance Implications of a Remote Middle Tier
If possible, avoid the overhead of interprocess and intercomputer communication. Unless your business requirements dictate the use of a remote middle tier, keep your presentation, business, and data access logic on the Web server. Deploy your business and data access assemblies to the Bin directory of your application. However, you might require a remote middle tier for any of the following reasons:
You want to share your business logic between your Internet-facing Web applications and other internal enterprise applications.
Your scale-out and fault tolerance requirements dictate the use of a middle tier cluster or of load-balanced servers.
Your corporate security policy mandates that you cannot put business logic on your Web servers.
If you absolutely have to split the application logic up anyways, you could use WCF as a transport mechanism. I'm not sure how it stacks up against remoting when it comes to performance. However, I seem to remember that this is the guideline Microsoft is pushing.
Clemens Vasters (Technical Lead for the Microsoft .NET Service Bus) talks about WCF vs. Remoting in this answer on MSDN forums.
Learn to write asynchronously.
Explore the CCR runtime for example.
Each thread that is blocked waiting for IO responses is one less available to your system.
Turn off 'idealised logging' leave the ability to switch it back on via admin console. But logging is often a hidden bottle neck.
CACHE CACHE CACHE!
If it was expensive to get the data the first time, don't pay for it the second!
Avoid ASP.net's Session State - This can seriously bloat and lead to a large slow down in page responsiveness.
Modify the http headers to specify short browser caching (5sec - 20sec) (Depends on the nature of the content)
Utilise GZIP while you are at it!
AND USE LOTS OF RAM
Here are my tips
1)Move all your static files - images , css, js to a load balancer like nginx. This will greatly reduce the load on IIS server and it will have enough free resources to serve the main request.
2)Think about caching and avoiding database access altogether.
3)Try to implement REST principles are far as possible.
4)Keep session state to a bare minimum - if possible avoid it altogether.
There are some good performance and scalability points in these articles from Omar Al Zabir.
10 ASP.NET Performance and Scalability Secrets
and
99.99% available ASP.NET and SQL Server SaaS Production Architecture
(also check out his book Building a Web 2.0 Portal with ASP.NET 3.5)