Short, honest write-ups of the ideas that come up in interviews and on the job. Each one teaches the concept properly, cites the Microsoft documentation, and points back to the class that drills it until it sticks.
Premium SSD bills by size tier, not usage — most fleets pay P30 prices for P10 workloads. Measure real IOPS at P95, map to the tier ladder, and know the resize asymmetry before you buy. When Premium SSD v2 ends the problem.
The VNet is free; everything attached to it bills. The billing map for peering, NAT Gateway, private endpoints, gateways and firewalls, how to trace each meter in Cost Analysis, and the three quiet monthly burners.
The honest comparison, plus the correction: Oracle quietly halved its Always Free allowance in June 2026 and most guides still quote the old figure. What each tier really gives, the catch behind each, and the free-practice discipline for Azure.
The fear that stops beginners isn't difficulty — it's the bill. The exact switches that make Azure a free lab, the always-free services, and the one hidden meter (Log Analytics) that catches people out.
Both cut the same bill. A reservation says "I will run this exact VM size in this exact region for a year"; a savings plan says "I will spend five dollars an hour on compute" — and the price of that easier promise is a shallower discount.
A budget is the thirty-second insurance policy against a runaway cloud bill — it emails you as actual or forecasted spend climbs toward your threshold. The catch everyone misses: it warns, it does not stop the spending.
Most overspend is not clever waste — it is idle VMs, over-sized everything, and pay-as-you-go prices on workloads that run all year. The levers that move the bill, in order of effort to payoff.