Are you familiar with the CAP theorem? How to implement a distributed system that satisfies all CAP properties? Name all three properties and explain how they are paired.

The CAP theorem states that a distributed system cannot simultaneously guarantee all three properties:

1. Consistency: All nodes see the same data at the same time.
2. Availability: Every request receives a response (success or error) without long delays.
3. Partition tolerance: The system continues to operate despite network partitions (loss of communication between nodes).

According to the theorem, during a network partition, the system must choose between consistency and availability.

• CP (Consistency + Partition tolerance): The system sacrifices availability to ensure consistency. For example, during a partition, some nodes may not respond to prevent data inconsistency.
• AP (Availability + Partition tolerance): The system sacrifices consistency, responding to requests even during a partition, which may lead to temporary inconsistencies.
• CA (Consistency + Availability): This mode is only possible in the absence of network partitions, i.e., in a homogeneous environment without network failures.

Implementing a system that satisfies all three properties simultaneously is impossible under real network partition conditions.

Example:

• A database oriented towards CP may block requests during a partition to maintain consistency.
• A database oriented towards AP will respond to requests even if the data may not be fully consistent.

Thus, when designing a distributed system, it is essential to determine which properties are more critical for the specific case and choose the appropriate architecture.