Explanation
A fault domain is a grouping of hardware and infrastructure within an availability domain. Each availability domain contains three fault domains. Fault domains provide anti-affinity: they let you distribute your instances so that the instances are not on the same physical hardware within a single availability domain. A hardware failure orCompute hardware maintenance event that affects one fault domain does not affect instances in other fault domains. In addition, the physical hardware in a fault domain has independent and redundant power supplies, which prevents a failure in the power supply hardware within one fault domain from affecting other fault domains.
To control the placement of your compute instances, bare metal DB system instances, or virtual machine DB system instances, you can optionally specify the fault domain for a new instance or instance pool at launch time. If you don't specify the fault domain, the system selects one for you. Oracle Cloud Infrastructure makes a best-effort anti-affinity placement across different fault domains, while optimizing for available capacity in the availability domain. To change the fault domain for an instance, terminate it and launch a new instance in the preferred fault domain.
Use fault domains to do the following things:
Protect against unexpected hardware failures or power supply failures.
Protect against planned outages because of Compute hardware maintenance.

OCI Web Application Firewall (WAF) is a cloud based, PCI compliant, global security service that protects applications from malicious and unwanted internet traffic.

Correct. User access and permissions are managed by the customers.

Explanation
To design a high availability architecture, three key elements should be considered- redundancy, monitoring, and failover:
1) Redundancy means that multiple components can perform the same task. The problem of a single point of failure is eliminated because redundant components cantake over a task performed by a component that has failed.
2) Monitoring means checking whether or not a component is working properly.
3) Failover is the process by which a secondary component becomes primary when the primary component fails.
The best practices introduced here focus on these three key elements. Although high availability can be achieved at many different levels, including the application level and the cloud infrastructure level, here we will focus on the cloud infrastructure level.
An Oracle Cloud Infrastructure region is a localized geographic area composed of one or more availability domains, each composed of three fault domains. High availability is ensured by a redundancy of fault domains within the availability domains.
An availability domain is one or more data centers located within a region. Availability domains are isolated from each other, fault tolerant, and unlikely to fail simultaneously. Because availability domains do not share physical infrastructure, such as power or cooling, or the internal availability domain network, a failure that impacts one availability domain is unlikely to impact the availability of others.
A fault domain is a grouping of hardware and infrastructure within an availability domain. Each availability domain contains three fault domains. Fault domains let you distribute your instances so that they are not on the same physical hardware within a single availability domain. As a result, an unexpected hardware failure or a Compute hardware maintenance that affects one fault domain does not affect instances in other fault domains.
You can optionally specify the fault domain for a new instance at launch time, or you can let the system select one for you.
All the availability domains in a region are connected toeach other by a low-latency, high bandwidth network.
This predictable, encrypted interconnection between availability domains provides the building blocks for both high availability and disaster recovery.

Explanation
Oracle Cloud Infrastructure FastConnect provides an easy way to create a dedicated, private connectionbetween your data center and Oracle Cloud Infrastructure. FastConnect provides higher-bandwidth options, and a more reliable and consistent networking experience compared to internet-based connections.