.Net Core in Azure App Service - WebJob

The objective of this exercise is to learn how to run .NET Core Application in Azure App Service – WebJob. WebJob provides ability to run a script (called job) in two different ways:

1. Trigger - run the job every time an API is called or a schedule is reached.
2. Continuous - make sure the job is always running (job should have a while loop but when it goes down we bring it back up).

Jobs are deployed by copying them to the right place in the file-system (or using a designated API which will do the same). These Jobs will run under the worker process of the SCM\Kudu Web Site and not the main site.

Running .NET Core Console App as WebJob -

A WebJob looks for specific file type, for example (.cmd, .bat, .exe, etc). To run a .NET Core console application use the DOTNET command. Therefore, you need to create a file with an extension a WebJob is looking for that executes, for example: dotnet exeWebJob.dll for my example I named it run.bat.

To deploy the .NET Core console application to an Azure App Service Web App Web Job access the Azure portal and navigate to the Azure App Service where you will host the WebJob.  Then click on the WebJobs link and the Add button.

Once the WebJob is successfully uploaded, it will render in the WebJob blade.Click on it and you will see the Run button. As this WebJob is a manually triggered job, you must click on the Run button in order for the job logic within the .NET Core console application to run.

When you write output to the console using the WriteLine() method, it will show in the Run Details window on KUDU/SCM.  After starting the .NET Core WebJob, click on the Logs link and a new browser tab is opened and you can see the most current state of the WebJob.

Lastly, you can see that the .NET Core WebJob is running within the DOTNET.EXE process by looking at the Process explorer in KUDU/SCM.  Click on the Properties button to view the command line.

Invoking from postman –

Note:

1. In case of any failure, you can see Run Details for the reason of failure.

2. WebJob Working Directory - There are 2 options for where the WebJob is running from (what is the working directory):

   A. The WebJob is copied to a temporary directory under %TEMP%\jobs\{job type}\{job name}\{random name} and will run from there This option prevents the original WebJob binaries from being locked which might cause issues redeploying the WebJob. For example updating an .exe file that is currently running.

   B. The WebJob is run directly from the WebJob binaries directory. We call this option in place. This option can have the locking issue and should only be used when there is no risk of locking the file. For example if the WebJob only consists of a .cmd file.

   By default the first option is used (in place = false) other than for .js node.js scripts (in place = true).

3. The Azure WebJobs SDK is a framework that simplifies the task of writing background processing code that accesses data in Azure services. The SDK features a declarative syntax for specifying events that should trigger a function, such as a new message added to a queue. Similar declarative syntax controls reading and writing data once a function has been triggered. This system of triggers and bindings takes care of most of the low-level coding tasks associated with accessing Azure and third-party services.

   Functions, triggers and bindings

   A WebJobs SDK project defines one or more functions. A function is a method that has a trigger attribute in its method signature. Triggers specify conditions for calling a function, and bindings specify what to read and write.For example, the trigger attribute in the following function tells the runtime to call the function whenever a queue message appears in the items queue.
   The Blob attribute tells the runtime to use the queue message to read a blob in the workitems container. The content of the queue message — provided in the queueTrigger parameter — is the name of the blob.

4. In case you are unable to read the content of Image keep pressing Ctrl + until it's readable.