Last week I built a highly available app on AWS. This week I did it again on Azure, and nothing carried over except the thinking. The names changed, the console changed, and the error messages changed. What stayed the same were the questions I had to ask: Where is the boundary? Who is allowed to talk to whom? What proves it works?

Here's what the week actually looked like, including the parts that didn't go to plan.

Part 1: Learning Azure's rules before building anything

My first real lesson came before a single resource existed. The portal's default VM size cost about $70 a month. The size the assignment asked for, a B1s, cost about $8. Then B1s showed as unavailable, first because of an availability zone setting, then because one region had no capacity for my subscription at all.

Instead of clicking through regions, I opened Cloud Shell and asked the CLI where B1s was allowed for my account.…