1.2 - Benefits of cloud computing (scalability, elasticity, availability)
AZ-900 objective 1.2 covers the benefits of using cloud services. You need to tell related terms apart: scalability adds capacity, and horizontal scaling (scaling out) puts more identical instances behind a load balancer, while elasticity automatically scales out and back in as demand rises and falls with no human involvement and no advance schedule. Agility is spinning up a full environment in minutes and tearing it down the same day. Reliability is the ability to recover from failures and keep working, and business continuity covers staffing, communications and alternate facilities so the whole organization keeps functioning, not just IT. Global reach means deploying in regions close to users worldwide for low latency. Governance improves because templates and policies enforce standards on every deployed resource. A 99.9 percent availability SLA allows about 8.76 hours of downtime per year. Expect scenarios that describe an automatic scale event or an availability promise and ask which benefit or characteristic it illustrates.
Scales out and back automatically with demand = elasticity; more identical instances behind a load balancer = horizontal scaling. Spin up and tear down in minutes = agility. 99.9 percent SLA = about 8.76 hours of downtime a year.
Practice questions
1. An e-commerce site automatically adds VM instances during flash sales and removes them when traffic drops, without any administrator action. Which cloud characteristic does this BEST illustrate?
- Elasticity (correct answer)
- High availability across redundant datacenters
- Predictive capacity planning done weeks in advance
- Geo-distribution of content to edge locations
Elasticity is the ability to automatically add and remove resources to match demand in real time, which is exactly what this automatic scale-out and scale-in describes. High availability is about surviving failures, capacity planning is manual and anticipated, and geo-distribution concerns content placement, not resource adjustment.
2. A retail company expects unpredictable traffic peaks on its cloud-hosted store. Which TWO cloud benefits directly help it absorb those peaks? (Choose TWO.)
- Elasticity, which adds and removes resources automatically (correct answer)
- Scalability, which lets the system grow to handle more load (correct answer)
- A CapEx-heavy purchase of spare servers kept powered off on site
- Manual quarterly capacity review meetings with the finance department
- Fixed resource allocation locked in at deployment time
Elasticity automatically adjusts resources to the actual load, and scalability means the platform can grow to absorb higher demand - together they handle unpredictable peaks. Buying idle spare servers, quarterly reviews, and fixed allocations are the rigid on-premises habits the cloud replaces.
3. An online florist sees traffic spike unpredictably around holidays and fall to near zero the rest of the year. Which benefit lets it match resources to demand automatically?
- Elasticity (correct answer)
- A large fixed pool of servers sized for the busiest holiday of the year
- Disaster recovery replication to a geographically distant second region
- Long-term reserved capacity purchased a full year in advance
Elasticity automatically adds resources when demand spikes and removes them when it drops, matching an unpredictable seasonal pattern. A fixed pool sized for the peak wastes money off season, disaster recovery is about surviving failures, and reserved capacity is a static commitment that cannot follow sudden swings.
4. A ten-person business with no IT staff needs professional email, calendars, and document collaboration available tomorrow. Which service model best serves this need?
- IaaS, by deploying and hardening a mail server on new virtual machines
- PaaS, by developing an in-house collaboration platform on managed services
- A private cloud built in the office to keep every mailbox on local disks
- SaaS (correct answer)
SaaS delivers ready-to-use applications like email and document collaboration with nothing to build or administer - ideal without IT staff. Running a mail server on IaaS or developing a platform on PaaS both require skills and time the company lacks, and a private cloud is the heaviest option of all.
5. An online booking system is designed with redundant components so that it keeps serving customers even when a virtual machine or a datacenter component fails. Which cloud concept does this design illustrate?
- Agility, because new environments can be provisioned within minutes whenever needed
- Elasticity, because resources are automatically added and removed to follow the demand curve
- High availability (correct answer)
- Consumption-based billing, because charges apply only to the resources that are used
High availability means the service stays accessible despite failures, thanks to redundancy that removes single points of failure. Agility is about speed of provisioning, elasticity is about matching capacity to demand, and consumption-based billing is a cost model - none of them describes surviving component failures.
6. An Azure service is covered by a 99.9% uptime SLA. What does this commitment primarily define?
- A promise that the service will never experience any downtime or planned maintenance during the subscription period
- The minimum availability Microsoft guarantees, with service credits if it is not met (correct answer)
- The average response time of the service measured across all Azure regions worldwide
- The percentage of support tickets that must be answered within one business day
An SLA (service-level agreement) states the availability level Microsoft commits to, typically as a percentage of uptime, and provides service credits when the commitment is missed. It is not a promise of zero downtime, and it does not measure response times or support ticket handling.