Why it matters
Interviewers for cloud support and junior DevOps roles almost always start with concepts: what is the difference between IaaS and SaaS, what is a region, who is responsible for patching. These ideas also shape real decisions, such as where to put a Ghanaian bank's data and how much work the team takes on. They are the core of entry exams like AZ-900.
Why companies use the cloud
Buying servers means paying a lot up front, waiting for delivery and guessing how much capacity you will need. In the cloud you pay as you go, add capacity in minutes and give it back when you no longer need it. Finance teams call this moving from capital expense (buying equipment) to operating expense (paying for use). The cloud also offers scalability (handle more users by adding resources), elasticity (adding and removing resources automatically as demand changes) and high availability (staying up when one part fails).
Service models
Think of feeding a team for a church harvest:
- IaaS (infrastructure as a service): you rent the kitchen and cook everything yourself. You get virtual machines and networks, and you manage the operating system and everything above it.
- PaaS (platform as a service): a caterer provides the kitchen and cooks; you bring the recipe. You give the platform your code and it runs it, handling servers and patching.