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A friend of mine was having issues connecting to a couple of VMs that he provisioned using an ARM template. The template worked perfectly until he added the JSON block to add an NSG.

Every time he started a deployment with the NSG block in the ARM template, he wouldn’t be able to connect to the VMs in any way. The fun fact was that even deleting the NSG didn’t solve the issue, so he had to recreate the whole environment from scratch and trust me that took a while 🙂

So what was the problem, you may ask?

He was using a source TAG Internet which for some reason (I still haven’t figured this one out), killed the connectivity on the VMs on both sides (Private and Public IPs) and funnily enough, the logs didn’t show anything.

If you encounter a problem like this one, double check your NSG blocks to not have sourceAddressPrefix: Internet but sourceAddressPrefix: *

Problematic example:

Working example:

So far I haven’t been able to reproduce it, and I’m still looking into what’s causing the issue for that particular ARM template but if you encounter something similar, give it a try and let me know your findings 🙂

Have a good one!

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