《Designing Data-Intensive Applications》

Reliablity means making systems work correctly, even when faults occur. Note that a fault is not the same as a failure. A fault is usually defined as one componet of the system deviating from its spec, whereas a failure is when the system as a whole stops providing the required service to the user.

Scalability means having strategies for keeping performance good, even when load increaes.

Maintainability has many facets, but in essence it's about making life better for the engineering and operation teams who need to work with the system.