What is the minimum number of virtual machines and availability zones (AZ-900)

Correct answer: D) Two virtual machines and Two availability zones.
SLA of 99.99%: This translates to a maximum downtime of 5.25 minutes per year. A single virtual machine in one availability zone would be susceptible to outages due to hardware failures, planned maintenance, or unexpected events.
High availability: To achieve 99.99% uptime, you need redundancy and fault tolerance. This means deploying your application on multiple VMs across different availability zones.
Availability zones: These are physically separated data centers within a region. If one zone experiences an outage, the others remain operational, ensuring your application remains available.
Therefore, deploying two virtual machines across two availability zones provides the necessary redundancy and fault tolerance for a 99.99% SLA. Any other option wouldn't meet the high availability requirement.

Here's a breakdown of the other options:
One VM and One availability zone: This leaves the application vulnerable to outages in the single zone.
Two VMs and one availability zone: While having two VMs improves resilience, a single zone outage would still affect both VMs.
Remember, achieving a 99.99% SLA requires both redundancy and geographically separate infrastructure. By deploying your application across two VMs in two different availability zones, you can maximize uptime and minimize the risk of service disruptions.