Need For Resiliency:
MicroServices are distributed in nature. It has more components and moving parts. In the distributed architecture, dealing with any unexpected failure is one of the biggest challenges to solve. It could be a hardware failure, network failure, etc. The ability of the system to recover from the failure and remain functional makes the system more resilient. It also avoids any cascading failures.
Why Bulkhead?
A ship is split into small multiple compartments using Bulkheads. Bulkheads are used to seal parts of the ship to prevent the entire ship from sinking in case of a flood. Similarly, failures should be expected when we design software. The application should be split into multiple components and resources should be isolated in such a way that failure of one component is not affecting the other.