Final answer:
The OCI construct designed to shield from failures within an availability domain is called a fault domain. Fault domains ensure instances are distributed across different physical hardware, improving resilience against hardware failures.
Step-by-step explanation:
The construct within Oracle Cloud Infrastructure (OCI) that protects against failures within an availability domain is the fault domain. In OCI, an availability domain is one or more data centers located within a region. Fault domains provide a way to distribute instances so that they are not on the same physical hardware within an availability domain. This aids in mitigating the risk of hardware failure affecting all instances at once. If one piece of hardware within a fault domain fails, only the instances in that fault domain are affected while instances in other fault domains continue to run unaffected.
OCI also offers other strategies for high availability. These include the use of multiple availability domains within a region, as well as cross-region replication to protect against the failure of an entire region. For databases, services like Oracle Data Guard can be employed for automatic failover in case of an outage.