VMSS Custom image pros/cons

Question

I need to install .net framework 4.7 on my VMSS. I tried using script extension but since I need to reboot the machine after the installation, it was a bit complex.

I decided to go with custom image. I created a VM, installed the .net framework and then captured it to image. Was painless process.

My question is, it seems that if my VMSS is using custom image, I cannot update it to use a marketplace image. Are there any other things I lose by using custom images?

Answer 1

George! Long time no see :).

This is a great question, but I don't think it's documented anywhere. I threw together a quick blog post describing the pros and cons: https://negatblog.wordpress.com/2018/06/28/custom-vs-platform-images-for-scale-sets/. Here's the summary:

• Platform images tend to allow for greater scale
• Some features only support platform images
• When using custom images, you control the image lifecycle, so you don't need to worry about the image being removed unexpectedly
• Deployment speed can differ between the two (either way can be faster depending on the scenario)
• With custom images, you can actually capture data disks along with the OS disk, allowing you to easily initialize each VM in the scale set with data

Hope this helps! :)

-Neil