Hands-On Microservices with Kubernetes

Understanding the CAP theorem

The CAP theorem states that a distributed system can't have all three properties at the same time:

• Consistency
• Availability
• Partition resiliency

In practice, you get to pick if you want a CP system or AP system. A CP system (consistent and partition resilient) is always consistent and will not serve queries or make changes if there is a network partitioning between components. It will function only when the system is fully connected. This obviously means that you don't have availability. On the other hand, an AP system (available and partition resilient) is always available and can operate in split-brain fashion. When the system splits, each part may continue to operate normally, but the system will be inconsistent ...