How should I inject a DbContext instance into an IHostedService?

A good way to use services inside of hosted services is to create a scope when needed. This allows to use services / db contexts etc. with the lifetime configuration they are set up with. Not creating a scope could in theory lead to creating singleton DbContexts and improper context reusing (EF Core 2.0 with DbContext pools).

To do this, inject an IServiceScopeFactory and use it to create a scope when needed. Then resolve any dependencies you need from this scope. This also allows you to register custom services as scoped dependencies should you want to move logic out of the hosted service and use the hosted service only to trigger some work (e.g. regularly trigger a task - this would regularly create scopes, create the task service in this scope which also gets a db context injected).

public class MyHostedService : IHostedService
{
    private readonly IServiceScopeFactory scopeFactory;

    public MyHostedService(IServiceScopeFactory scopeFactory)
    {
        this.scopeFactory = scopeFactory;
    }

    public void DoWork()
    {
        using (var scope = scopeFactory.CreateScope())
        {
            var dbContext = scope.ServiceProvider.GetRequiredService<MyDbContext>();
            …
        }
    }
    …
}

You can add create Scope in constructor as below:

 public ServiceBusQueueListner(ILogger<ServiceBusQueueListner> logger, IServiceProvider serviceProvider, IConfiguration configuration)
        {
            _logger = logger;
            _reportProcessor = serviceProvider.CreateScope().ServiceProvider.GetRequiredService<IReportProcessor>();
            _configuration = configuration;
        }

Do add

using Microsoft.Extensions.DependencyInjection;