Skip to main content

(Part 1) Azure Service Fabric - Parent Child communication and cancellation

Part 1 - http://vunvulearadu.blogspot.ro/2016/03/azure-service-fabric-parent-child.html
Part 2 - http://vunvulearadu.blogspot.ro/2016/03/part-2-azure-service-fabric-parent.html

A few weeks ago I so an interesting question on MSDN forum that I think that is pretty common. In this post I will try to give a possible solution to this problem.
Context:
There are multiple instances of the same Restful Stateful Services that are running in parallel. A new instance is created by a 'parent service that also might specifies the action that needs to be executed.
Problem:
The parent service needs to be able to cancel the instance of our Restful Stateless Service based on external factors or based on the current state of the child.


What we need
Basically we need to:

  • Store and map all the service instances that are created by a service
  • Store in a specific location a state related to them
  • Share their state with the parent service
  • Give the ability to the parent to cancel a child service
Sharing the state
To be able to share the state between different instances of the same service we can use Reliable Collections. In our case Reliable Dictionary might be a good solution for our problem. We can store as a key value pair the state of each service instance. 
Each instance has the ability to update his state directly. Any concurrency problem like temporary inconsistency are resolved out of the box by Reliable Dictionary.

Cancellation
When we create an instance of a Restful Stateful Service we can use RunAsync method. This method allow us to specify a cancellation token. This token can be used by the child service to see if a cancellation was requests.
protected override async Task RunAsync(
      CancellationToken cancellationToken)
{
    ...
}

Unique identification of each child service
In our Reliable Dictionary we need to identify unique each service. We could generate a unique ID for each service instance. It might work, but we would need to send this ID to each service instance in the moment when we would call RunAsync method.
Another possible solution is to use the CancellationToken that we already have as a key. The instance of cancellation token is known by parent and child  we can use it easily as the key.


Using this approach we can have a mechanism that allow us to have a simple and cheap communication between our services. The main flow would look like this:

  1. [Parent] Create a CancellationToken
  2. [Parent] Add the CancellationToken to our Mapping State dictionary 
  3. [Parent] Start a new instance of your stateless service and give us parameter the CancellationToken
  4. [Service Instance] Do his logic
  5. [Service Instance] Add specific information to the Mapping State dictionary to the item with the same CancellationToken
  6. [Parent] Detect that a condition is TRUE
  7. [Parent] Get the CancellationToken of the service instance that needs to be canceled
  8. [Parent] Send the CancellationToken to the service instance
  9. [Service Instance] Detect the cancellation request and stop


This solution can be very useful when we need to migrate a heavy services from a monolithic architecture to a solution hosted on a micro-service system.
The only problem with this solution is related to the type of service. We cannot use multiple types of Reliable Services for this because a Reliable Collection can be shared and accessed only by the same service type.

Tomorrow we will see another solution for this problem without having to use Reliable Collection and the same Reliable Service.

Part 1 - http://vunvulearadu.blogspot.ro/2016/03/azure-service-fabric-parent-child.html
Part 2 - http://vunvulearadu.blogspot.ro/2016/03/part-2-azure-service-fabric-parent.html

Comments

Popular posts from this blog

How to check in AngularJS if a service was register or not

There are cases when you need to check in a service or a controller was register in AngularJS.
For example a valid use case is when you have the same implementation running on multiple application. In this case, you may want to intercept the HTTP provider and add a custom step there. This step don’t needs to run on all the application, only in the one where the service exist and register.
A solution for this case would be to have a flag in the configuration that specify this. In the core you would have an IF that would check the value of this flag.
Another solution is to check if a specific service was register in AngularJS or not. If the service was register that you would execute your own logic.
To check if a service was register or not in AngularJS container you need to call the ‘has’ method of ‘inhector’. It will return TRUE if the service was register.
if ($injector.has('httpInterceptorService')) { $httpProvider.interceptors.push('httpInterceptorService&#…

ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded

Today blog post will be started with the following error when running DB tests on the CI machine:
threw exception: System.InvalidOperationException: The Entity Framework provider type 'System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer' registered in the application config file for the ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded. Make sure that the assembly-qualified name is used and that the assembly is available to the running application. See http://go.microsoft.com/fwlink/?LinkId=260882 for more information. at System.Data.Entity.Infrastructure.DependencyResolution.ProviderServicesFactory.GetInstance(String providerTypeName, String providerInvariantName) This error happened only on the Continuous Integration machine. On the devs machines, everything has fine. The classic problem – on my machine it’s working. The CI has the following configuration:

TeamCity.NET 4.51EF 6.0.2VS2013
It seems that there …

Run native .NET application in Docker (.NET Framework 4.6.2)

Scope
The main scope of this post is to see how we can run a legacy application written in .NET Framework in Docker.

Context
First of all, let’s define what is a legacy application in our context. By a legacy application we understand an application that runs .NET Framework 3.5 or higher in a production environment where we don’t have any more the people or documentation that would help us to understand what is happening behind the scene.
In this scenarios, you might want to migrate the current solution from a standard environment to Docker. There are many advantages for such a migration, like:

Continuous DeploymentTestingIsolationSecurity at container levelVersioning ControlEnvironment Standardization
Until now, we didn’t had the possibility to run a .NET application in Docker. With .NET Core, there was support for .NET Core in Docker, but migration from a full .NET framework to .NET Core can be costly and even impossible. Not only because of lack of features, but also because once you…