Under the hood: Box’s HHVM migration

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Box successfully migrated their entire PHP codebase to HHVM, resulting in significant reductions in latency and increases in infrastructure capacity. The migration involved addressing numerous compatibility issues between HHVM and the standard PHP interpreter, including behavioral differences in less popular PHP corners and fundamental design choices like multiprocessing models and memory allocation. Box also revamped their deployment process to accommodate HHVM's JIT compilation warm-up requirements and the benefits of regular restarts. This involved a shift from a symlink-based deployment to a multi-instance HHVM setup that allows for warm-up, rollbacks, and canary deployments.