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This new system greatly improved upon the free-for-all it replaced. For the purposes of this book, suffice it to say that implementing this improvement meant replacing Obidos, acb, and many other key pieces of our software infrastructure piece by piece while it was still running our business nonstop. This required a major investment in development resources, systems architecture planning, and great care to ensure that the monolith continued to stand until its last surviving function had been replaced by a service. The rolling regeneration of the way we built and deployed technology was a bold move, an expensive investment that stretched over several years of intensive and delicate work.
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Colin Bryar (Working Backwards: Insights, Stories, and Secrets from Inside Amazon)