A while back, Microsoft Azure team announced preview of WebJobs and Hanselman blogged about it. Since then, I always wanted check out Web Jobs and finally I did it recently. And ..holy mother of god!
WebJobs are cron jobs. For operation(s) that are to be performed repetitively or in a scheduled manner WebJob is good proposition. WebJobs have been packaged along with Azure websites. The popular use case Microsoft is targeting to use WebJobs is as backend for the Websites.
Let’s say you have an e-com website and you are receiving tons of orders. For better scalability, your website (front end) would submit those order to let’s say a Azure queue. You would then have WebJob(s) configured as backend to read messages off top of the queue and process them. Or you can have a nightly cron job, which goes through the orders and sends a digest or suggestions in an email etc. Or you can have it to do a monthly invoicing. So all those backend jobs that you do not want to perform in front end for obvious reasons can be done using WebJobs.
Even if WebJobs comes packaged along with Azure Websites – nobody is stopping us from using them without websites. For doing certain operations repetitively, Azure PaaS already offers what is termed as Worker Role. But I personally find worker roles very ceremonial. They do make sense when you want to perform long running, heavy-duty operations and you need horizontal/ vertical scaling to do that. But for doing tiny, repetitive, loopy code blocks or doing certain things in scheduled manner worker roles are expensive (time, money-wise). Worker roles are powerful, no doubt, but with great power comes great responsibility. (Can’t believe I just said that ) Primarily what they offer is an infinite while loop and then it’s your responsibility to implement scheduling, triggers etc. WebJobs are light-weight, deployment-friendly and provide in-built mechanism to schedule stuff.
Implementing popular use cases using WebJobs
Conceptually, WebJob (the way I understood them) is an infinite while loop that listens for an event or trigger. You can make this listener trigger again and again continuously or you can schedule it if that’s the story you want to tell.
For all sorts of WebJobs development, Azure Web Jobs SDK and respective nuget packages needs to be pulled.
Here is an example of a WebJob that is implemented as a command line .NET exe. This one reads a message off top of a storage queue and writes that entity to the Azure table storage. Every time a new message is available in the queue the ProcessQueueMessage() method is trigged automatically along with the respective trigger inputs.
Interestingly WebJobs support multiple ways to deliver the package. (I prefer and like the command line .NET exe, but suit yourself).Using Azure management portal you can drop a file in a certain location on the IIS box and rest is magic. Following file types are supported :
- .exe – .NET assemblies
- .cmd, .bat, .exe
Once the deployment is done one can manage the WebJob – start, stop, delete etc.
Using Website => WebJobs => Add a job switch a new job can be added.
A WebJob can be set to run continuously or scheduled.
Schedule can be as granular as your requirement demands. Interestingly a WebJob can be configured as recurring or as a one-time-deal as well.
Quick word of caution. Webjobs are deployed on the IIS box, so make sure you are not doing such an operation as part of it that hogs all the memory and CPU. Good news though is it does not use IIS’s thread pool. For scaling WbJobs you need to scale your website.
Feel free to ping me in case of any help.