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I'm playing with WebJobs SDK v3.0.5, using a very simple .NET Core 2.2 Console project as follows:

TimerHost.csproj

<Project Sdk="Microsoft.NET.Sdk">
 <PropertyGroup>
 <OutputType>Exe</OutputType>
 <TargetFramework>netcoreapp2.2</TargetFramework>
 <LangVersion>7.1</LangVersion>
 </PropertyGroup>

 <ItemGroup>
 <PackageReference Include="Microsoft.Azure.WebJobs" Version="3.0.5" />
 <PackageReference Include="Microsoft.Azure.WebJobs.Extensions" Version="3.0.2" />
 <PackageReference Include="Microsoft.Extensions.Logging.Console" Version="2.2.0" />
 </ItemGroup>

 <ItemGroup>
 <None Update="appsettings.json">
 <CopyToOutputDirectory>Always</CopyToOutputDirectory>
 </None>
 </ItemGroup>
</Project>

Program.cs

using System.Threading.Tasks;
using Microsoft.Azure.WebJobs;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace TimerHost

 public class Program
 
 public static async Task Main()
 
 var builder = new HostBuilder();
 var host = builder
 .UseEnvironment("Development")
 .ConfigureServices((context, services) =>
 
 services.AddSingleton(context.Configuration);
 )
 .ConfigureWebJobs(webJobsBuilder =>
 
 webJobsBuilder
 .AddAzureStorageCoreServices()
 .AddTimers();
 )
 .ConfigureLogging((context, b) =>
 
 b.SetMinimumLevel(LogLevel.Debug);
 b.AddConsole();
 )
 .UseConsoleLifetime()
 .Build();

 await host.RunAsync();
 
 

 public static class Function
 
 public static void Run([TimerTrigger("*/10 * * * * *")] TimerInfo timer, ILogger logger)
 
 logger.LogInformation($"Running job for timer. Next 3 runs are: timer.FormatNextOccurrences(3)");
 
 

appsettings.json

The trigger runs fine. However, according to the latest docs (https://docs.microsoft.com/en-us/azure/app-service/webjobs-sdk-how-to#multiple-instances), the timer should run implicitly as a singleton, which means it should be using an Azure storage account for distributed locking support.

When using Azure Functions locally, I would expect to provide a setting like this:

 "AzureWebJobsStorage": "UseDevelopmentStorage=true"

Otherwise I actually can't run a function, I get an error saying this setting is required, however in the Console host example, I don't get any error at all.

Can someone explain why the console host is not requiring the use of a default storage account? How is the timer maintaining singleton behavior in this scenario?

I spent some time debugging the WebJobs SDK source code from my app, and found more information on what is happening under the hood:

• If the AzureWebJobsStorage app setting is not defined in the configuration, then the SDK falls back to using an in-memory distributed lock manager for timer and singleton triggers. There is no logging associated with this fallback, and the default lock manager is suitable for local development only.




• Azure Storage Emulator can be used instead by setting the connection string as you would for Azure Functions, just make sure you've re-built your project so that the appsettings.json files are propagated to the project output folder, this tripped me up for a bit.




• No errors or log entries are emitted if the value of AzureWebJobsStorage is not a valid local or cloud-based storage account connection string - the configuration will just silently fall back to the in-memory lock manager instead.