I have following problem:
I need to synchronize access to cache objects that are accessed by WCF-service operations. The calling clients provides a parameter that maps to which cache object(s) operation will use.
In short, requests should be queued by the parameter and then executed in synchronous manner.
What would be best way to implement this? I don't want to expose the queue to the client and I want solution that easily scales if there are multiple service instance running in different machines with shared cache.
Related
We have migrated/refactored one of our micro-service from request per thread model (sync) to Reactive (async). Development is complete and started stress testing the reactive service. We are looking for the help on how to perform the activity for reactive APIs
What we have done?
Our service makes HTTP call for an external service. During our stress test, we mocked the external service call. Instead of making a network call, we introduced delay using Thread.sleep() method and returning mock response in our service component(where we make actual HTTP call to the external service).
With this approach, we are observing our reactive service is getting crashed even with very small requests volume. Just to add, we follow similar approach while testing other sync services (request per thread model).
What can we try next?
To have infrastructure closer to what will be live environment, I would suggest to run separate mock server, preferably on separate machine, so it will not steal resources from your service.
You can do it easily with wiremock - see running as standalone page.
When you run wiremock as proxy, you can record and playback real requests from your service.
To make this mock more real, you can add delay for mock responses - it will simulate external service "processing time".
reactive services have a very small thread pool which is optimized to be utilized at 100%.
If you introduce something blocking like Thread.sleep() you are basically removing this ability. What makes reactive, "reactive" is its ability to switch execution threads if something is blocking.
Thread.sleep() holds the thread where it is, and it cant switch to doing something else, basically crippling its entire functionality.
You should never Thread.sleep() in a reactive application, unless you are using OnSubscribe and placing each call on a separate scheduler, which in turn sort of makes your reactive application "non-reactive" and instead fallbacks to default standard servlet application behavior.
I have developed a WCF service for consumption within the organization's Ethernet.
The service is currently hosted on a windows-service and is using net.tcp binding.
There are 2 operation contracts defined in the service.
The client connecting to this service is a long running windows desktop application.
Employees(>30,000) usually have this client running throughout the week from Monday morning to Friday evening straight.
During this lifetime there might be a number of calls to the wcf service in question depending on a certain user action on the main desktop client.
Let us just say 1 in every 3 actions on the main desktop application would
trigger a call to our service.
Now we are planning to deploy this window service on each employee's desktop
I am also using `autofac` as the dependency resolver container.
My WCF service instance context is `PerSession`, but ideally speaking we have both the client and service running in the same desktop (for now) so I am planning to inject the same service instance for each new session using `autofac` container.
Now am not changing the `InstanceContext` attribute on the service implementation
because in future I might deploy the same service in a different hosting environment where I would like to have a new service object instance for each session.
Like mentioned earlier the client is a long running desktop application and I have read that it is a good practise to `Open` and `Close` the proxy for each call but if I leave the service to be PerSession it will create a new service instance for each call, which might not be required given the service and client have a 1-1 mapping. Another argument is that I am planning to inject the same instance for each session in this environment, so Open & Close for each service call shouldn't matter ?
So which approach should I take, make the service `Singleton` and Open Close for each call or
Open the client-side proxy when the desktop application loads/first service call and then Close it only when the desktop application is closed ?
My WCF service instance context is PerSession, but ideally speaking we have both the client and service running in the same desktop (for now) so I am planning to inject the same service instance for each new session using autofac container
Generally you want to avoid sharing a WCF client proxy because if it faults it becomes difficult to push (or in your case reinject) a new WCF to those parts of the code sharing the proxy. It is better to create a proxy per actor.
Now am not changing the InstanceContext attribute on the service implementation because in future I might deploy the same service in a different hosting environment where I would like to have a new service object instance for each session
I think there may be some confusion here. The InstanceContext.PerSession means that a server instance is created per WCF client proxy. That means one service instance each time you new MyClientProxy() even if you share it with 10 other objects being injected with the proxy singleton. This is irrespective of how you host it.
Like mentioned earlier the client is a long running desktop application and I have read that it is a good practise to Open and Close the proxy for each call
Incorrect. For a PerSession service that is very expensive. There is measurable cost in establishing the link to the service not to mention the overhead of creating the factories. PerSession services are per-session for a reason, it implies that the service is to maintain state between calls. For example in my PerSession services, I like to establish an expensive DB connection in the constructor that can then be utilised very quickly in later service calls. Opening/closing in this example essentially means that a new service instance is created together with a new DB connection. Slow!
Plus sharing a client proxy that is injected elsewhere sort of defeats the purpose of an injected proxy anyway. Not to mention closing it in one thread will cause a potential fault in another thread. Again note that I dislike the idea of shared proxies.
Another argument is that I am planning to inject the same instance for each session in this environment, so Open & Close for each service call shouldn't matter ?
Yes, like I said if you are going to inject then you should not call open/close. Then again you should not share in a multi-threaded environment.
So which approach should I take
Follow these guidelines
Singleton? PerCall? PerSession? That entirely depends on the nature of your service. Does it share state between method calls? Make it PerSession otherwise you could use PerCall. Don't want to create a new service instance more than once and you want to optionally share globals/singletons between method calls? Make it a Singleton
Rather than inject a shared concrete instance of the WCF client proxy, instead inject a mechanism (a factory) that when called allows each recipient to create their own WCF client proxy when required.
Do not call open/close after each call, that will hurt performance regardless of service instance mode. Even if your service is essentially compute only, repeated open/close for each method call on a Singleton service is still slow due to the start-up costs of the client proxy
Dispose the client proxy ASAP when no longer required. PerSession service instances remain on the server eating up valuable resources throughout the lifetime of the client proxy or until timeout (whichever occurs sooner).
If your service is localmachine, then you consider the NetNamedPipeBinding for it runs in Kernel mode; does not use the Network Redirector and is faster than TCP. Later when you deploy a remote service, add the TCP binding
I recommend this awesome WCF tome
I have a driver that I need to access via a web site that is not thread-safe. Since many people can be on the site at a given time I figured I would create a WCF service that would handle all the calls. Most of the calls would be asynchronous calls to add items to a work queue. Some would be synchronous calls to get a list of items still unprocessed or items that have been processed.
Since the driver isn't thread safe, the service must take in potentially many requests at once and either add items to the work queue, return the work queue, or return the work-completed queue. A single-threaded operation in the service needs to read from the work queue, processes the job using this non-thread-safe driver, and, when complete, update the work-completed queue.
While I conceptually have clear in my mind what to do, the specifics of implementation confuse me a little. I think I should host the service in IIS since it will have to respond to web requests and otherwise act like any other web site, but I'm not sure how to guarantee that the access of the driver will remain single-threaded without blocking web requests. Do I need a second service, perhaps a Windows service, that would process all access to the driver and use the IIS-hosted WCF service to get the next queue item and update the queue when processing is complete?
I'd consider:
Clients call your aspx pages,
Pages call to wcf service (netMsmqBinding)? - to avoid blocking and waiting (singke service, can be hosted where you want).
When server done - it's notify clients (websocket? SignalR?)
I'm writing an application which will use the Azure Service Bus. For local development I'm using Windows Server Service Bus to provide the same services (the code to use either is identical).
I want to write the application to be tolerant of transient errors when sending or receiving messages. To that end, I want to be able to test the fault-handling code can deal with the local Service Bus instance suddenly being unavailable during execution of various operations.
Ideally, I'd want to write some automated integration tests around these scenarios, but I appreciate that may not be practically achieved.
What can I do to simulate transient errors on my local Service Bus?
One easy thing would be to call the stop-sbservice (affects one node) or stop-sbfarm (affects the entire farm) cmdlets. This would let you simulate a servicebus outage locally. You can then call start-sbservice or start-sbfarm to bring the service back and validate that your code recovers properly. This approach also has the added benefit that you control when the service returns (compare to just crashing the process). This page has information on the available cmdlets.
If that's not enough, another approach that I've used in the past is to shut down the network interface, or, if the server is in another machine, put up a firewall on the ports used to communicate to service bus.
So I'll be providing a few functions via a self hosted (in a WindowsService) WebServiceHost (not sure how to process HTTP GET/POST with ServiceHost), one of which may be called a large amount of the time. This function will also rely on a connection in the appdomain (hosted by the WindowsService so it can stay alive over multiple requests).
I have the following concerns and would be oh so thankful for any input/thoughts/comments:
Concurrent access - how does the WebServiceHost handle a bunch of concurrent requests. Are they queued and processes sequentially or are new instances of the contracts automagically created?
WebServiceHost -> WindowsService communication - I need some form of communication from the WebServiceHost to the hosting WindowsService for things like requesting a new session if one does not exist. Perhaps implementing a class which extends the WebServiceHost with events which the WindowsService subscribes to... (unless there is another way I can set off an event in the WindowsService when a request is made...)
Multiple WebServiceHosts or Contracts - Would it give any real performance gain to be running multiple WebServiceHost instances in different threads (one per endpoint perhaps?) - A better understanding of the first point would probably help here.
WSDL - I'm not sure why (probably just need to do more reading), but I'm not sure how to get the WebServiceHost base endpoint to respond with a WDSL document describing the available contract. Not required as all the operations will be done via GET requests which will not likely change, but it would be nice to have...
That's about it for the moment ;) I've been reading a lot on WCF and wish I'd gotten into it long ago, but definitely still learning.
Concurrent access - this is something you can set using ServiceBehaviorAttribute. there are a number of options -- you can have WCF create a new instance of your service class for each incoming request, or you can have a single instance handle all requests. Additionally you can tell WCF whether to pass you the requests serially or concurrently.
WebServiceHost -> WindowsService communication. Two approaches spring to mind: WCF supports a mode called "well known instance" where you pass an instance of your service to the ServiceHost constructor instead of passing a Type and letting WCF instantiate it for you. With this mode you can preconfigure your service instance with a reference back to your hosting code (alternatively you could use events). An alternative if you want to preserve instancing flexibility would be to have a static method in your hosting code that the WCF service could call back into.
Multiple WebServiceHosts or Contracts - really no advantage to having more than one ServiceHost instance. see also this SO thread: What are the benefits for several servicehosts? Does one ServiceHost support several simultaneous connections on one endpoint?.
WSDL - While you can enable WSDL by turning on metadata publishing (http://msdn.microsoft.com/en-us/library/ms788760.aspx), WSDL support is intended for SOAP-based services, not pure HTTP GET/POST. The WSDL that gets auto-generated for your service will likely not be very useful.