Twitter, PayPal, and Netflix had serious problems. Problems like scaling, quality, and downtime became common and increasing issues. Each had a large, single-code base application known as a “monolith.” And each hit different frustration points where a fundamental architecture change had to occur. Development and deployment cycles were long and tedious, causing delays in feature delivery. Each deployment meant downtime or expensive infrastructure to switch from one set of servers to another. As the code base grew, so did the coupling between modules. With coupled modules, code changes are more problematic, harder to test, and lower overall application quality.