Difference in Azure Availability Sets and Scale Sets

Question

Can someone define the difference between the two in the ARM portal. Also what would be the PowerShell if i need to add a new Azure RM VM to a existing AS(Availability Set)? Tha

Answer 1

After reading all of the answers here, I still didn't feel confident in my knowledge. I got the impression that a scale set would be safe because it had multiple fault domains by default, but couldn't understand why people were still going for availability sets.

To put my mind at ease, I hacked around with the azure CLI and found that you can run this command to list the instances of your scale set and actually verify they are in different fault domains:

az vmss get-instance-view --subscription "your-subscription-id" \ 
--resource-group "your-rg" --name "your-scale-set-name" \
--instance-id "*" | grep platformFaultDomain
    "platformFaultDomain": 0,
    "platformFaultDomain": 1,
    "platformFaultDomain": 2,
    "platformFaultDomain": 4,
    "platformFaultDomain": 0,
    "platformFaultDomain": 1,
    "platformFaultDomain": 3,
    "platformFaultDomain": 4,
    "platformFaultDomain": 2,
    "platformFaultDomain": 3

Hope that puts someone else's mind at ease as well!

I provided some more info and links here as well if you're interested in further resources: https://coding-stream-of-consciousness.com/2019/02/27/azure-scale-set-vs-availability-set/