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I think I know the answer to this one, but I have just spotted someone doing exactly the opposite - who is a very skilled developer, were they just having a bad day?

Q: Is it OK to call a service from within a service in an SOA architected system?

I suspect not, but i'll ask anyway...

John Saunders
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I can't think of any reason why not. I can think of multiple reasons why a service could call another service. I've architected and implemented multiple services that do this. I'm also aware of other architectures that set up this sort of system.

Mark
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  • you don't think that, considering the architecture should be vertically sliced appropriately, that this would create a spaghetti architecture? –  Jan 11 '11 at 17:28
  • I think if you run saws vertically through your servers, you'll have other problems to deal with. I also think pasta will be bad for the internals. Do you have concrete examples of what problems you think might arise? – Mark Jan 11 '11 at 17:32
  • one issue i have is that for instance if on my website, i call a wcf service, which calls a wcf service, which could potentially call a wcf service... etc. etc. –  Jan 12 '11 at 11:51
  • And, to put this another way... Say on your service, you access a database server. Isn't that just another "service"? It didn't go over SOAP, but conceptually, it's no different. "Services" call other "services" all the time. Just because we arbitrarily label one thing as a "service" and not another thing doesn't change the architecture conceptually. – Mark Jan 12 '11 at 15:33
  • i'm thinking latency here - it's not like calling into an object that resides in the same app pool. Are we at the point now where the fee for calling into services across boundaries is so minimal that we don't even care whether or not the interface we're calling into is remote? –  Jan 12 '11 at 15:40
  • I can't tell you if it's fast enough or not, because I don't know anything about your performance requirements, nor do I know anything about the performance characteristics of your services. What I can tell you, however, is that services can be *extremely* fast even out-of-process, and you can't make a blanket statement like "services can't call services" because that's NEVER been true. – Mark Jan 12 '11 at 16:18
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Definitely yes. This SOA pattern is commonly called choreography where one web service processes and then passes the message to another down a processing pipeline. Google it and you will find some good references.
Another case may be more technical reason like routing, where you have frontend webservices that routes your messaged to different backend services based on security policy, content, bridge different technology or transport protocol etc.

softveda
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The answer to this is as always "it depends..." let me explain what I mean.

Calling another service in a SOA is of course a totally acceptable thing to do, it is at the heart of SOA to be able to compose new things out of existing services.

The more important part is how you call the services, consider a SOA system where multiple services collaborate in a call chain call each one enlisting the other in the transactional scope. Doing this sort of thing without careful planning will have a massive impact on your systems performance. The same call chain designed using well partitioned services that are scoped at the correct unit of work suffers less.

Consider system robustness, in a typical architecture one service tends to become more popular than others and lands up having many other services calling it. A failure of this one service brings down the entire system due to all the other services being dependent on the call to this one service.

Consider the difference between synchronous and asynchronous calls, when do you use what? That is the impact of each?

How do you design and partition services to limit the cost of crossing the service boundary on each call?

Lots of questions, but if you look around there are many places to find answers, I suggest starting with these.

I would suggest you read articles by Thomas Erl and Roger Sessions, this will give you a firm handle on what SOA is all about.

Building a SOA

SOA Design Pattern

Achieving integrity in a SOA

Why your SOA should be like a VW Beetle

SOA explained for your boss

WCF Service Performance

MetalLemon
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think about the architectural goal of "separation of concerns". instead of each service knowing how to do everything, it can rely on other specialized services for shared pieces of functionality

Robert Levy
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  • I don't agree with this at all. One of the core tenets of Service Orientation is that services are autonomous. You are creating dependancies on other web services if you "rely" on other specialized services for shared pieces of funcationality. – user1431072 Apr 27 '15 at 18:40
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I have some different scenario. What if you want to implement service level clustering in your SOA? For example, say persistence service is resides on one machine and is responsible for handling all persistence tasks in the cluster. So, on other machine which needs persistence functionality, need to connect to the that machine only(ignore fail over factor).

Now while login, if User service has instance of Persistence service directly, then you will not be able to implement service level clustering.

We have our SOA middleware and I called service from each other directly. But when we implemented service level clustering using JMS/ActiveMQ, we faced the problem for those interconnected services.

Nikunj
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