Introduction

The EShopworld.WorkerProcess contains classes for the management of worker process interactions

Installation

Get the latest version of the package from https://

Install-Package EShopworld.WorkerProcess

IWorkerLease

The IWorkerLease component allows distinct instances of IWorkerLease components to cooperatively acquire and release a mutual exclusion lease for a period of time.

Since there is no central lease manager each of the IWorkerLease instances must cooperate to acquire and release lease instances. Worker lease instances will schedule themselves to acquire leases at the configured Leaseinterval.

For example if the LeaseInterval is 10 minutes each of the IWorkerLease instances will schedule the first lease acquire cycle for the next whole interval with in the hour. So if the workers start the lease cycle at 12:01, each IWorkerLease will wait until 12:10 to start the lease cycle.

NOTE: Since the IWorkerLease instances synchronise the acquiring of leases based on the local time of the machine it is important that the clocks be syncronised via NTP. Any inaccuracy in the clocks will effect the lower bound for the LeaseInterval and or the concurrency of the lease acquisition by the various IWorkerLease instances.

Usage

To use the WorkerProcess component the first step is to add the various components to the Di container. Note that this step depends on your DI framework and your hosting environment.

In the public void ConfigureServices(IServiceCollection services) method include the following lines:

    // Include the worker process services
    services.AddWorkerLease();

NOTE: The above creates a singleton instance of the IWorkerLease component. This is fine for a single executing process but will not give the correct behavior when multiple IWorkerLease instances are required for managing separate worker threads.

    // One off initalisation of the ILeaseStore instance
    await leaseStore.InitialiseAsync();

    // Attach the lease allocated callback
    workerLease.LeaseAllocated += (sender, args) =>
    {
        _output.WriteLine($"[{DateTime.UtcNow}] Lease allocated until [{args.Expiry}]");
        // Start doing work
    };

    workerLease.LeaseExpired += (sender, args) =>
    {
        _output.WriteLine($"[{DateTime.UtcNow}] Lease expired");
        
        // Stop doing work
    };

    // Start this worker lease instance leasing
    workerLease.StartLeasing();

Initialise default ILeaseStore

The default ILeaseStore is based on CosmosDb document database. This store needs to be initialised once off to create the database and collection to store the worker process leases.

    // Initalise the lease store instance
    await leaseStore.InitialiseAsync();

Configuration Options

WorkerLeaseOptions

  "WorkerProcess": {
    "WorkerLease": {
      "WorkerType": "SchedulerWorker",
      "LeaseInterval": "0:30:00",
      "ElectionDelay": "0:0:10" 
    },
    "Region": {
      "West Europe": {
        "Priority": "2",
        "InstanceId": Guid1
      },
      "Southeast Asia": {
        "Priority": "3",
        "InstanceId": Guid2
      },
      "East US": {
        "Priority": "4",
        "InstanceId": Guid3
      }
    }
  }

Configuration Setting	Description	Default
WorkerType	This is a category type of a worker that acquires leases	There is no default value and the worker type should be set to a domain specific value
Priority	This is the priority of the worker process	The default is zero which is the highest priority
LeaseInterval	The amount of time in minutes that the lease is acquired	Defaults to 5 mins
ElectionDelay	It's the election time duration. The lease will only be assigned after all the instances have had enough time to vote announcing their presence with their priority	Defaults to 5 seconds

Please note that Priority and InstanceId can also be set region specific. In the json snippet above, we have 3 regions each of them setting their own instance Id and priority