u/Djinjja-Ninja

Customer had an Azure HA deployment that couldn't be in-place upgraded.

Originally an R81.10 deployment with the double whammy of unsupported disk config and 32 bit VMs, so had to do a redeployment upgrade because the in place upgrade refused to even import.

Marketplace deployment kept failing because it kept trying to deploy with an already used IP address of the original deployment.

They had originally deployed it with a terraform template, but turns out they had a slight misunderstanding about Azure reserving the first 4 addresses, so the original template they used .5 as the first address for the HA deployment. The first 4 reserved addresses are .0 though .3, so you should deploy with .4 as the first subnet address.

Turns out that the marketplace ARM template only checks for the first unused address in the subnet, which turned out to be .4, so the rest of the deployment fails because it doesn't check whether the rest of the addresses it assumes are free weren't actually free, because .5 through .7 were already used by the exits deployment.

Fixed it in the end by creating an unattached network interface with the .4 address to force the ARM template to pick the next available 3 (4 for the backend) addresses for the deployment which fell after the existing HA deployment.

That was a rabbit hole and a half. 3rd party was blaming the ARM template, and I was blaming their original install (turns out I was right).

I've deployed about 10 HA templates today to get to the bottom of this bastard to replicate this issue.

While it annoyed the shit out of me, I very much enjoyed working this out.

So remember kids, when Azure says "Azure reserves the first four addresses" that includes the network address.

Thought he might have something interesting to impart, but no it's basically an advert for everything Weber.

He using briquettes and gas for fucks sake.