CODEWITHSUNDEEP
azure-service-fabric
Sean Feldman
Sean Feldman

Reputation: 26012

Embedding custom metadata with Service Fabric application/service

The objective that I have is to run multiple applications with some metadata embedded into applications/services so that I could query applications/services using the metadata. Is this possible?

I was looking at the following post and the answer hints at this possibility, but no specific details on how to achieve the result.

Upvotes: 2

Views: 171

Answers (1)

Vaclav Turecek
Vaclav Turecek

Reputation: 9050

The primary piece of "metadata" you get is the service/application instance name. That's what I talked about in my other post. The way that works is by creating each service/application instance with a name that contains some information clients can use when resolving them. Clients can then query Service Fabric for named application/service instances and connect to a specific one. A service/application instance name is URI, so you can use a path hierarchy to categorize information.

Continuing with the audio/video example: Let's extend that example so we have an application that can perform specific tasks for specific media formats for audio or video. Each combination of task + media format is a unique named service instance, resulting in a deployment that looks something like this:

Application:
fabric:/avapp
  Services:
  fabric:/avapp/video/encoding/mp4
  fabric:/avapp/video/encoding/h264
  fabric:/avapp/video/captioning/english
  fabric:/avapp/video/captioning/czech
  fabric:/avapp/audio/encoding/aac
  fabric:/avapp/audio/encoding/mp3
  etc.

Now clients can query Service Fabric to discover what services are available:

FabricClient fabricClient = new FabricClient();

System.Fabric.Query.ServiceList services = await fabricClient.QueryManager.GetServiceListAsync(new Uri("fabric:/avapp"));

Then you can simply query the list of services with LINQ. For example, if I want to see all services that do video encoding:

services.Where(x => x.ServiceName.AbsolutePath.Contains("video/encoding"));

And then you can resolve an address for a specific service to connect to it:

ServicePartitionResolver resolver = ServicePartitionResolver.GetDefault();
ResolvedServicePartition servicePartition = await resolver.ResolveAsync(new Uri("fabric:/avapp/video/encoding/h264"), new ServicePartitionKey(1), cancellationToken);
ResolvedServiceEndpoint endpoint = servicePartition.GetEndpoint();

There's a bit more to the address resolution part (see here), but that's the general idea.

Application instances also allow you to set custom application parameters (key-value pairs) that can be set per instance at creation time. They don't show up in the application name, but you get that information back when you ask Service Fabric for a list of running application instances. That can potentially also be used as metadata by clients when they need to decide what application to connect to.

Update: More info on application instance parameters:

When you create a new application instance you can supply a set of key-value pairs in the application description. Then when you query Service Fabric for application instances you get back a list of Application result objects that have said parameters. This also shows up in Visual Studio, in your application project, where you have environment-specific application parameter files. Visual Studio extracts those key-value pairs from the XML files and uses them in the application description when it creates an instance of your application.

enter image description here

Upvotes: 2

Related Questions