Software Engineering at Google

Chapter 15. Deprecation

Written by Hyrum Wright

Edited by Tom Manshreck

I love deadlines. I like the whooshing sound they make as they fly by.

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All systems age. Even though software is a digital asset and the physical bits themselves don’t degrade, new technologies, libraries, techniques, languages, and other environmental changes over time render existing systems obsolete. Old systems require continued maintenance, esoteric expertise, and generally more work as they diverge from the surrounding ecosystem. It’s often better to invest effort in turning off obsolete systems, rather than letting them lumber along indefinitely alongside the systems that replace them. But the number of obsolete systems still running suggests that, in practice, doing so is not trivial. We refer to the process of orderly migration away from and eventual removal of obsolete systems as deprecation.

Deprecation is yet another topic that more accurately belongs to the discipline of software engineering than programming because it requires thinking about how to manage a system over time. For long-running software ecosystems, planning for and executing deprecation correctly reduces resource costs and improves velocity by removing the redundancy and complexity that builds up in a system over time. On the other hand, poorly deprecated systems may cost more than leaving them alone. While deprecating systems requires additional effort, it’s possible to plan for deprecation during the design of the ...