I have a set of services I want to be able to access via one end point altogether.
Now I want to build something in wcf rather than use an existing framework/software so that is out of the question.
Suppose I have 10 contracts each representing a contract of an indepedent service that I want to "route" to, what direction should I go?
public partial class ServiceBus : ICardsService
{
//Proxy
CMSClient cards = new CMSClient();
public int methodExample()
{
return cards.methodExample();
}
So far I've tried using a partial class "ServiceBus" that implements each contract but then I have more than a few (60+) recurrences of identical function signatures so I think I should think in a different angle.
Anyone got an idea of what I should do? or what direction to research? currently I'm trying to use a normal wcf service that's going to be configured with a lot of client end points directing to each of the services it routes TO - and one endpoint for the 'application' to consume.
I'm rather new at wcf so anything that may seem too trivial to mention please do mention it anyway.
Thanks in advance.
I have a set of services I want to be able to access via one end point
altogether.
...
So far I've tried using a partial class "ServiceBus" that implements
each contract
It's questionable whether this kind of "service aggregation" pattern should be achieved by condensing multiple endpoints into an uber facade endpoint. Even when implemented well, this will still result in a brittle single failure point in your solution.
Suppose I have 10 contracts each representing a contract of an
indepedent service that I want to "route" to, what direction should I
go?
Stated broadly, your aim seems to be to decouple the caller and service so that the caller makes a call and based on the call context the call is routed the relevant services.
One approach would be to do this call mediation on the client side. This is an unusual approach but would involve creating a "service bus" assembly containing the capability to dynamically call a service at run-time, based on some kind of configurable metadata.
The client code would consume the assembly in-process, and at run-time call into the assembly, which would then make a call to the metadata store, retrieving the contract, binding, and address information for the relevant service, construct a WCF channel, and return it to the client. The client can then happily make calls against the channel and dispose it when finished.
An alternative is to do the call mediation remotely and luckily WCF does provide a routing service for this kind of thing. This allows you to achieve the service aggregation pattern you are proposing, but in a way which is fully configurable so your overall solution will be less brittle. You will still have a single failure point however, unless you load balance the router service.
I'm not sure about making it client side as I can't access some of the
applications (external apis) that are connecting to our service
Well, any solution you choose will likely involve some consumer rewrite - this is almost unavoidable.
I need to make it simple for the programmers using our api
This does not rule out a client side library approach. In fact in some ways this will make it really easy for the developers, all they will need to do is grab a nuget package, wire it up and start calling it. However I agree it's an unusual approach and would also generate a lot of work for you.
I want to implement the aggregation service with one endpoint for a
few contracts
Then you need to find a way to avoid having to implment multiple duplicate (or redundant) service operations in a single service implementation.
The simplest way would probably be to define a completely new service contract which exposes only those operations distinct to each of the services, and additionally a single instance of each of the redundant operations. Then you would need to have some internal routing logic to call the backing service operations depending on what the caller wanted to do. On second thoughts not so simple I think.
Do you have any examples of a distinct service operation and a redundant one?
Related
I think elements of this question have been answered elsewhere, but I couldn't find an answer to my specific circumstance.
I work with an enterprise application. This application interfaces with various 3rd party APIs & services via what is currently a single class and a plethora of proxy dlls. This means that each of these dlls is referenced in the main project. In addition to this, over time as we've added new service calls, a lot of code has been duplicated, with only very small amendments. Most of the service calls do roughly the same thing and take largely the same objects as parameters.
As you can imagine, this presents us with a number of problems, not least of which is the time it takes to add a new service.
We have a task now to refactor and streamline this process to make it more manageable and resilient - I have an idea in my head and I've done a lot of research but I just wanted to see if anyone had any better ideas or similar experiences before I dive in.
What I want to do is add a facade layer so that the base code gets all the data commonly used and bundles it off to the facade along with a parameter stipulating which service it wants to call. The facade would then pass the data to either the proxies or a bridge, which would transform it into the right format for the target service, make the required calls in order, and return any responses back to the facade to pass on.
Although I have an idea of the architecture I want, I'm not 100% sure which way to go in terms of concrete C# code - whether to add the facade and bridge/adapter code in a new project which also has the proxy dlls referenced, or whether to go down the base/interface route and add the required transformation classes directly into the proxy dlls.
Edited to add: I am unable to consider consolidating this functionality into a service or microservice due to wider infrastructure considerations that I am unable to discuss here.
Any suggestions appreciated!
WCF beginner's question: I've been told that changing the WCF contract is costly and requires constant maintenance (recreating the proxy in the client side), and therefore the preferred method is having one very generic point-of-contact method (which decides how to act, say, according to a given enum parameter).
This sounds quite smelly to me, but I haven't been able to find any information about this issue (bad choice of search keywords? probably).
Any advice, or maybe a useful link?
Thanks!
You don't need to generate the proxy again, you can simply ensure the client is built with the correct interface version. If you're very careful and only add methods, not remove or modify, that works just fine too. That's a lot of responsibility to manage, of course.
To use an interface rather than generate a client proxy, check my question from a while ago:
WCF Service Reference generates its own contract interface, won't reuse mine
You are confusing some terms here and I think you might be referring to a known flaw which has been fixed in .Net 3.5 SP1.
Recreating the WCF proxy used to be an expensive operation at runtime. This has been improved in .Net 3.5 to cache the proxy objects transparently MSDN Blog.
If you are referring to the "code maintenance" of the proxy, then all you are referring to is implementing an interface at the client. If you need to maintain the interface then this comes back to basic SOA. If your services provide access and as much information as possible, assuming that your service will be used for purposes you haven't yet considered then you will likely not need to modify the interface after it is created. You should also consider your upgrade paths as well.
Juval Lowy has a good discussion about this problem in his book which is a little dense but has some pretty good information in it.
A piece of advice: WCF has a whole lot of features designed to make your code really simple and elegant. If you are worreid about maintenance, what you may be driven to do is write an interface:
string ServiceMethod(string xml) //returns XML
Don't do this. Take the time to design a good maintainable interface and a good data/message contract. This will let WCF provide all the extras you get for free when hosting your service for interaction.
Generic (as in non-specific, monolithic) interfaces are hard to understand and program to. The reason not to define a single method as the API is that it's impossible for clients to understand what's going on, and when you change the (implicit) API of this interface, your clients will break in horrible ways that you won't detect at compile time.
It's been a while since I touched WCF, but if your clients are internal (same codebase, versioning and deployment schemes), then regenerating the WCF proxies is very easy, and having a "strong" detailed API will make your life so much easier than a generic one.
It depends on what kind of change you mean. Change to the service contract is indeed costly and should not happen. Service contracts are (or should be) at a sufficiently high level of granularity that change is very rare.
More common are changes to the types which are exposed on the service. These changes are more common and therefore you do need to approach your change in such a way as to avoid breaking existing clients if possible.
There are several ways you can do this, such as exposing your types polymorphically using an interface, but the simplest way is to simply ensure that changes to your types on add new data member fields and make the new fields non-mandatory. If you can limit your changes to these then this is has the lowest impact to existing clients and enables new clients to use the new fields.
Hope this helps.
This is true that modifying the service contract (interface) would also required the client to recreate the proxy class at their end using the new published WSDL and may even require the client to change their code as par the new proxy. I don't think you can create such a generic interface that can handle all changes further down the road in the contract. A contract has to be written very carefully so that it doesn't change often and if there is a need to change the contract then it is better to deploy the service with a different version so that your old client can still work with the old version.
I'm working on a system right now that is in a single process space; we are breaking this up into several processes, initially to run on the same box but ultimately to distribute across several separate machines. I'm leaning towards using an ESB (NServiceBus, Rhino ESB) or possibly rolling my own with WCF + queues to handle the pub/sub and request/response scenarios our app has.
However, I'm struggling with the abstraction: I don't want the various components to know they are talking over the bus. The current APIs connecting the various services translate pretty well to this kind of model, but I want to hide that from the client and server sides. Short of writing a lot of custom proxy code for the client and server, is there a better way to approach this? I realize WCF can auto-generate proxies based on the service definition, but I really like some of the other stuff I get with (say) rhino servicebus.
Ideally, I'd like to be able to swap out different implementations (with and without an ESB/messaging layer) just using IoC (knowing there would have to be limits enforced by convention on what can be passed across the interfaces), but I'm not sure where to go with that. I'd really prefer to not have to change every method call on the current interfaces into its own discrete message class, either.
Any resources/patterns/tools to help me do this? Please ask questions if I'm not clear. Thanks.
There may not be one solution/off-the-shelf component that might help you.
Problem 1:
The basic problem can be solved via an ESB, as it provides location transparency and service aggregation. A regular ESB mediates/brokers requests between service consumer and service provider.
Take a simple example:
Service_A depends on Service_B
Service_C depends on Service_B
Service_B depends on Service_D
In this scenario, the best way to progress is this:
Define contracts exposed by Service_B and Service_D as external dependencies (possibly as a web service, though an ESB supports multiple protocols) in services Service_A, Service_C and Service_B, and consume via an ESB.
In ESB, to start with, route thes services Service_B and Service_D on the same instance.
If you migrate Service_D and Service_B as Service_Dx and Service_Bx on a different location, the ESB can be reconfigured to route to the new location. Also, an ESB can be configured to route to Service_B or Service_Bx based on some set of parameters (eg., test data to Service_B and production data to Service_Bx)
Problem 2:
The problem of IOC could probably be hard to achieve; there may not be a need.
I presume the clients, instead of consuming from a known location, are injected with the whereabouts of service location. This in reality transfers the configuration to client side. With this, for every new client added to the system there needs to be a separate configuration control. This might lead to logistical issues.
Please post your final solution, very interested to know your approach.
I have description of my Application Services using my fancy classes (ServiceDescription class that contains collection of ServiceMethod description, for simplification).
Now, I want to expose one Application Service as one WCF Service (one Contract). The current solution is very lame - I have console application that generates *.svc file for each Application Service (ServiceDescription). There is one method (Operation) generated for one ServiceMethod.
This works well but I would like to make it better. It could be improved using T4 template but I'm sure that there is still better way in WCF.
I would still like to have one *.svc file per one Application Service but I don't want to generate methods (for corresponding Application Service methods).
I'm sure that there must be some interfaces that allow to discover operations dynamically, at runtime. Maybe IContractBehavior...
Thanks.
EDIT1:
I don't want to use generic operation contract because I would like to have the ability to generate service proxy with all operations.
I'm sure that if I write WCF service and operations by hand then WCF uses reflection to discover the operations in the service.
Now, I would like to customize this point in order not to use reflection, just use my "operations discovering code" instead.
I think there is nothing wrong with static code generation in that case. In my opinion, it is a better solution than dynamic generation of contracts. Keep in mind that your contract is the only evidence you have/provide that a service is hosting a particular set operations.
The main issue I see about the dynamic approach is about versioning and compatibility. If everything is dynamically generated, you may end up transparently pushing breaking changes into the system and create some problems with existing clients.
If you have a code generator when you plan on implementing some changes in the application services, it will be easier to remember that the changes you make on the services may have a huge impact.
But if you really want to dynamically handle messages, you could use a generic operation contract (with the Action property set to *), and manually route the messages to the application services.
Keep in mind that you would lose the ability to generate from the service a proxy containing a list of operations available.
A project I am working on requires a structure as such:
{BasePrefix}/Application/{id}/Security/Users/{userId}
{BasePrefix}/Application/{id}/Objects/{objectId}
etc.
Application.svc would be end up being my WCF Web Service. I tried to convince them to do:
{BasePrefix}/Security/Application/{id}/Users/{userId}
This would allow me to have multiple WCF Web Services as Security.svc, Objects.svc, etc.
They still want it all under application so instead of throwing all my service methods into a single file, I wanted to break it out by functionality and use partial classes to combine it all into one resource.
I saw an article about how to do this here: http://www.meineck.net/2008/04/wcf-hosting-multiple-wcf-services-as.html
The developer in that article is working with a Net TCP binding, however, so I am not sure if this will work with a WebHttpBinding and how IIS will handle the multiple resources.
Has anyone done this? Is the article I linked a good resource? Or is there a better alternative method to achieve the same results?
The methodology in the linked article is sound, and will work for bindings other than netTcpBinding (including webHttpBinding, wsHttpBinding and so on).
However, I believe what you are trying to do is use a URL rewriting scheme (probably using the UriTemplate property), which is subtly different from what that article actually talks about. It is referring to the creation and implementation of multiple interfaces, by the same service, and mapping each interface to its own endpoint.
The approach does not work with a single endpoint. So if your endpoint is {BasePrefix}/Application, that can only be mapped to one interface (say IApplicationService) in the configuration.
In your case, I don't think you'll be able to go the multiple-interface route because you need to have just one endpoint. So you'll still need a single monolithic interface with all of the methods (ugly), but you could in theory use partial classes to split up the implementation of those methods into logical groups. It's better, but not exactly ideal.
You were on the right track with your original assessment. If your scheme looked like:
{BasePrefix}/Security/Application/{id}/Users/{userId}
{BasePrefix}/Repository/Application/{id}/Objects/{objectId}
Then you would be able to use either of the approaches - either have multiple services, or have a single service that implements multiple interfaces and hosts multiple endpoints.
What the code/configuration in that article is really designed to do is enable a single service instance to host multiple endpoints. The main reason to do this is if you would otherwise have to duplicate a lot of code between services. Unfortunately that's not your goal here, so you will either have to push harder for your proposed URI scheme, or deal with a monolithic service contract (interface) and do the best you can to keep the implementation clean through #region directives and/or partial classes.