Teams often consider external caches when the existing database cannot meet the required service-level agreement (SLA). This is a clear performance-oriented decision. Putting an external cache in front of the database is commonly used to compensate for subpar latency stemming from various factors, such as inefficient database internals, driver usage, infrastructure choices, traffic spikes, and so on.

Caching might seem like a fast and easy solution because the deployment can be implemented without tremendous hassle and without incurring the significant cost of database scaling, database schema redesign, or even a deeper technology transformation. However, external caches are not as simple as they are often made out to be. In fact, they can be one of the more problematic components of a distributed application architecture.