Running Startup Jobs¶

NCronJob allows you to configure jobs to run at application startup. This is useful for tasks that need to be executed immediately when the application starts, such as initial data loading, cleanup tasks, or other setup procedures.

Startup jobs are defined like regular CRON jobs and inherit from IJob. The only difference is that they are configured to run at startup. All startup jobs must be completed prior to the start of any other CRON (or instant) jobs.

public class MyStartupJob : IJob
{
    public Task RunAsync(IJobExecutionContext context, CancellationToken token)
    {
        // Perform startup task
        return Task.CompletedTask;
    }
}

As with CRON jobs, they must be registered in the AddNCronJob method.

builder.Services.AddNCronJob(options => 
{
    options.AddJob<MyStartupJob>()
           .RunAtStartup(); // Configure the job to run at startup
});

var app = builder.Build();
// Execute all startup jobs
await app.UseNCronJobAsync();
app.Run();

The RunAtStartup in combination with UseNCronJobAsync method ensures that the job is executed as soon as the application starts. This method is useful for scenarios where certain tasks need to be performed immediately upon application launch.

Failure to call UseNCronJobAsync when startup jobs are defined will lead to a fatal exception during the application start.

Of course, the call to RunAtStartup can also be chained to the registration of a standard CRON job. This setup may be useful, for instance, when one wants to prime a cache before the application starts, and then regularly refresh its content.

It may happen that the specified startup job runs task that are required for the application setup. For those cases, when one cannot tolerate a startup job to fail, the RunAtStartup method accepts an optional parameter shouldCrashOnFailure. When set to true, the specified job is expected to complete in a successful state. Otherwise, an exception will be thrown preventing the application start.

Example Use Case¶

Consider an application that needs to load initial data from a database or perform some cleanup tasks whenever it starts. You can define and configure a startup job to handle this:

Job Definition¶

public class InitialDataLoader : IJob
{
    private readonly IDataService _dataService;

    public InitialDataLoader(IDataService dataService)
    {
        _dataService = dataService;
    }

    public async Task RunAsync(IJobExecutionContext context, CancellationToken token)
    {
        await _dataService.LoadInitialDataAsync();
    }
}

Registering the Job¶

In your Program.cs or Startup.cs file, register the job and configure it to run at startup:

builder.Services.AddNCronJob(options => 
{
    options.AddJob<InitialDataLoader>()
           .RunAtStartup(shouldCrashOnFailure: true);
});

This setup ensures that: - The InitialDataLoader job will be executed as soon as the application starts, loading the necessary initial data. - Would anything prevent the job to successfully complete, the application will fail to start.

Summary¶

Startup jobs are a powerful feature of NCronJob that enable you to execute critical tasks immediately before application startup. By using the RunAtStartup method, you can ensure that your application performs necessary setup procedures, data loading, or cleanup tasks right at the beginning of its lifecycle.

This feature is particularly useful for applications that require certain operations to be completed before they are fully functional. By configuring startup jobs, you can streamline your application’s initialization process and improve its overall reliability and performance.