The Site Reliability Workbook

Chapter 7. Simplicity

By John Lunney, Robert van Gent, and Scott Ritchie with Diane Bates and Niall Richard Murphy

A complex system that works is invariably found to have evolved from a simple system that worked.

Gall’s Law

Simplicity is an important goal for SREs, as it strongly correlates with reliability: simple software breaks less often and is easier and faster to fix when it does break. Simple systems are easier to understand, easier to maintain, and easier to test.

For SREs, simplicity is an end-to-end goal: it should extend beyond the code itself to the system architecture and the tools and processes used to manage the software lifecycle. This chapter explores some examples that demonstrate how SREs can measure, think about, and encourage simplicity.

Measuring Complexity

Measuring the complexity of software systems is not an absolute science. There are a number of ways to measure software code complexity, most of which are quite objective.¹ Perhaps the best-known and most widely available standard is cyclomatic code complexity, which measures the number of distinct code paths through a specific set of statements. For example, a block of code with no loops or conditionals has a cyclomatic complexity number (CCN) of 1. The software community is actually quite good at measuring code complexity, and there are measurement tools for a number of integrated development environments (including Visual Studio, Eclipse, and IntelliJ). We’re less adept at understanding whether the ...