If I want to schedule a task to run say once every 30 minutes. I could do this with a basic timeout or use a node module like node-schedule.
But If I deploy my app to the cloud, such as Amazon AWS or Azure, and scale the instances to say 10, will this task then be scheduled to run 10 times, one for each instance? How can I avoid this, or am I thinking about how cloud instanced work in the wrong way.
If you want to use an Azure component, you could use the Azure scheduler:
Create jobs that run on your schedule
Azure Scheduler lets you create
jobs in the cloud that reliably invoke services inside and outside of
Azure—such as calling HTTP/S endpoints or posting messages to Azure
Storage queues. You can choose to run jobs right away, on a recurring
schedule, or at some point in the future.
Azure Scheduler
It entirely depends on your code but I'd imagine that yes it will run on each instance, probably slightly out of sync too.
This article describes quite nicely the problems with scheduled tasks:
http://dejanglozic.com/2014/07/21/node-js-apps-and-periodic-tasks/
My advice would be to try and avoid scheduled tasks as much as possible.
Related
I have this .NET long running API process/function that usually runs 30 mins in one execution that is hosted in AKS. This API is usually executed from the users coming from the front end of the app.
Due to concurrent executions from users, this is causing exhaustion of the app so I'm planning to implement a some sort of a queueing mechanism with the help of a scheduler(s).
What possibly is applicable Azure service that can execute my API in AKS on a scheduled basis (let's say every minute) and possibly check the database for some flagging values.
I need a way to check the table for some flagging value if there a currently running process or its been completed so it can process the next one, otherwise ignore the call until current on is complete.
I was looking into Azure Web Apps, Web Jobs or Batch Jobs but kinda confused which is applicable with my case.
Please advise thank you in advance.
There are a couple of options here.
Hangfire
Hangfire is an open-source library that can run background jobs in queues. In your case, you can enqueue each request from the client in a queue. Then Hangfire server will process them one by one (even with retry if the job fails). Hangfire supports SQL Server or Redis. You can query the storage to see the status of the queued jobs.
Hangfire can also run scheduled jobs, which will take care of that only one job run at a time.
Azure Service Bus
A more expensive option is to use Azure Service Bus for your queueing capability. For scheduled jobs, you can use AKS CronJobs but you will
implement the check yourself to see if there is a job already running.
Overall, I would recommend Hangfire, which can meet your requirements and is cheaper.
I have a Website (on Azure) where you can trigger asyncronous jobs, that needs a lot of traffic (copy files from one location to another).
So you press a button on the site and then I want to trigger a new job. What would be the best solution?
Solution 1) Use web jobs. But then there may problems with huge traffic, so that the website will not be reachable.
Solution 2) Use cloud service. Is it a good solution to start a new instance for each job? The jobs will not need a lot of cpu usage, but the traffic will be the point.
Solution 3) Is there any solution on azure, where you can just trigger a job, and ervery time it is triggered, a new instance will start, do the job and shutdown. Like fire and forget?
Put a job message in an Azure Storage queue. Use an Azure Cloud Service worker role to consume the message and do whatever processing needs to be done.
Can anybody explain the difference between Azure Web Jobs and Azure Scheduler
Azure Web Jobs
Only available on Azure Websites
It is used to run code at particular intervals. E.g. a console application every day
Used to trigger and run workloads.
Mainly recommended for workloads that either scale with the website or are relatively small.
Can be persistently running if "Always On" selected, otherwise you will get the 20 min timeout.
The code that needs to be run and schedule are defined together.
Azure Scheduler
Is not tied to Websites or Cloud Services
It allows you to call a website or add a message to a storage queue
Used for triggering events or triggering small workloads (e.g. add to queue), usually to trigger larger workloads
Mainly recommended for triggering more complex workloads.
This is only a trigger, and a separate function listening to trigger events (e.g. queue's) needs to be coded separately.
For many instances I prefer to use the scheduler to push to a storage queue and a worker role on each instance takes off the queue. This keeps tasks controlled granularly and can also move up or down in scale outside of your website.
With WebJobs they scale up and down with your site and hence your background tasks can become over taxed if your website is experiencing low traffic and scaled down.
Azure Scheduler - Provides a way to easily schedule http calls in a well-defined schedule, like every hour, every Friday at 9:00 am, Once a day, ...
Azure WebJobs - Provides a way to run small to medium work load (in the form of a script: .exe, .cmd, .sh, .js, ...) at the same context of an Azure Website (but can be hosted even with an empty website).
While a WebJob can run continuously (with a process that has a while loop) and Azure will make sure this WebJob is always running (with "Always On" set).
There is also an integration between Azure scheduler and Azure WebJobs where you have a WebJob that is running some finite work and the schduler is responsible for scheduling this work (invoking the WebJob).
So in summary, the scheduler is about scheduling work and WebJobs is about running work load.
A very simple question:
Why would someone use the Azure Scheduler if Azure WebJobs are free?
I couldnt find any topic regarding "azure webjobs vs azure scheduler"
The main difference is that the webjob contains everything that the scheduler can do:
Scheduler can make HTTP calls
WebJob can do that and more (run SQL commands, etc)
The actual scheduling bits of WebJobs are built on top of the scheduler. When you set up a Web Job on a schedule under the hood it uses the scheduler to kick it off. WebJobs provides a nice little location to host the code that gets executed. In fact, if you create WebJobs for a web site look in the Scheduler on the portal and you'll see them listed there as well.
Also note that the scheduler could call out to other systems not running Azure. If you have something running in a Cloud Service that needs to be called regularly, or even if something was hosted elsewhere (another provider or on premises) the scheduler is where you can set that up.
Regarding the cost aspect, there is a free tier to the scheduler as well: http://www.windowsazure.com/en-us/pricing/details/scheduler/.
It's 2016. The below answers are no longer accurate.
WebJobs now also has a built-in scheduler and the schedule can be defined by a cron expression.
When publishing to Azure, you can choose if you want to have the WebJob sparked off by the Scheduler or by the WebJob internal scheduler.
Important Note: The Azure Scheduler has limits to frequency of either 1hr or 1min depending on if paid or not. For the internal scheduler however, your App Service requires Always On to keep on running and firing off the job. This Always On status may affect your pricing.
Continuous jobs are monitored, and if they exit they are re-executed. In this way they act more like "services" in your local machine. There is a module that monitors and keeps your app working. Always-ON is a feature that will help your site stay alive and hence, your webjobs to continuously run.
Scheduler is used to trigger the webjobs. It uses the scheduler user account (not the back-end account). This way you can move out of the free tier for scheduler, sign up to higher tiers to suit your needs. But essentially, all the scheduler is doing is hitting an https endpoint (which is public, but required your auth).
Triggered jobs (scheduled and on demand) are invoked by an https call. These calls are load balanced - much in the same way that a web app with many instances is load balanced. Continuous jobs run concurrently by default, but can be set to be a singleton.
For Webjobs starting from version 2, there is no reason to use an Azure Scheduler anymore. As a matter of fact, the Azure Portal already flags this functionality as (Legacy).
From WebJob SDK v2 additional triggers have been introduced and one of them is TimerTrigger, which works with CRON expressions to schedule executions. This execution mode does not need any additional Azure construct, you just need the webapp to be set as AlwaysOn to guarantee the webjob to run.
Another azure service that works with TimerTriggers is Azure Functions, which is built on top of the WebJob SDK that allows a serverless execution.
Is there a way to use the windows scheduled task to kick off a url or a exe on a schedule?
Can I write a program as an exe then create a Azure VM then RDP into the Azure VM and hook it up to windows task scheduler?
Azure does have a scheduler now.
It allows invoking a Web Service over HTTP/s and post a message to a Windows Azure Storage Queue. It's very new but it can be free if you do not need the scheduler to be executed often. Otherwise it's a small monthly fee which come with scheduled task that can be up to every minute.
Things got much easier lately, please see this link https://azure.microsoft.com/en-us/services/scheduler/ to create a scheduled job in the new Azure Scheduler. There is a basic Free tier as well as some paid options but I think this is exactly what many of us were looking for. It is an excellent solution for triggering URLs with GET,POST,PUT,DELETE requests.
Just follow the simple instructions. Starting by selecting "Scheduler" from the Azure dashboard app menu:
Today the scheduler has been Azure Logic Apps:
https://learn.microsoft.com/en-us/azure/logic-apps/logic-apps-overview
If you are looking for something like a cron job (which is a job, that is being run at specific time again and again), then check out Azure Functions:
https://learn.microsoft.com/en-us/azure/azure-functions/functions-overview
Google Azure Storage Queues. They allow you to schedule jobs that will run at a later date. You can even specify when the job should run.