Azure Automation and Function Apps offer server-less script execution.
This post explains key differences between Azure Automation and Function Apps, concludes with an opinion on the preferred choice for a Scheduled Task replacement.
Comparing site by site
Usage / Use cases
Both allow the execution of scheduled jobs which themselves are based on scripts. PowerShell is supported on both options.
Azure Automation is triggered either by time or via web-hook. The “result” is like when working with Scheduled tasks. From file-operations to changes in the Azure infrastructure or any other job which is deterministic.
Function Apps also allow time trigger, but also offer a eventgrid integration and some native events, like for instance “on new file in storage account”. Also they can expose web endpoint. That means you could pass in parameters via HTTP Post or in the Query string and get result as JSON for example. There is also the concept of “durable functions” which more or less means that there are always ready to deliver results.
Audience
Azure Automation are targeting IT-Pros, formerly known as System Administrators.
Function Apps on the other hand are more developer focused. SREs or DevOps are also included here.
Manageability
Azure Automation uses “Accounts” as container objects for RunBooks. Settings that apply to all RunBooks such as Environment-Variables, Secrets or shared PowerShell modules.
Activating “Managed Identity” allows granting permissions on other Azure services like for instance allowing starting and stopping of VMs.
A RunBook itself is as dedicated Azure object that contains the script which may bound to a schedule and the execution choice.
Function Apps require an App Server Plan as foundation. The plan defines supported frameworks and dictates the costs. On the other hand, it allows vertical and horizontal scaling!
Dependencies and other settings are defined in *.json files and require little research.
Typically, only one script is stored on a Function App. Multiple scripts are possible but require attention when maintaining them in the different folder structures.
Complexity Level
Azure Automation in general is “simpler” in setting up and maintaining. Mostly because multiple jobs can be managed from one console. Another important aspect is that many aspects configurable via graphical user interface.
Once figured out how they work, using them is convenient.
Function Apps require more considerations when setting up and while maintaining. Most aspects must be done via configuration files. Setting up a schedule for instance requires knowledge of Cron syntax. In my experience PowerShell module dependencies are regular problematic. It is advisable to only import those which are essential for the script to work.
Mastering them have a steeper learning curve.
Various Differences
Azure Automation know the concept of “Hybrid Worker”. Behind that term are ARC enabled Windows Servers which allow the execution of scripts on them. This allows access to resources within the datacenter / the active directory / the private cloud with benefiting for all advantages that Azure technologies brings.
Using Hybrid Woker may also required to overcome limitations that are given such as the amount of available memory or concurrent jobs. – More on: https://github.com/MicrosoftDocs/azure-docs/blob/main/includes/azure-automation-service-limits.md
Supported languages: PowerShell and Python
GIT integration with bidirectional sync. – Deployment pipeline managed automatically.
Function Apps offer a rich set of integrations with Azure PaaS services. As they run within the context of an App Service Plan there are horizontal and vertical scaling options available to overcome also very demanding jobs.
Supported languages: PowerShell, C#, NodeJS, Python and more.
GIT integration with bidirectional sync and support for complex pipelines within Azure DevOps allow also sophisticated scenarios.
Conclusion
In my opinion is Azure Automation the best fit to be the better alternative to tradition Scheduled Task. Version Control, Change-Tracking, Security, Monitoring, Redundancy options and much more are reason for it.