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macOS CI Bare Metal Migration

2 posts · Oct 2013 – Apr 2020

What this trail covers

Spotify's Client Platform tribe continues to enhance the CI/CD experience for mobile apps. This post details the successful migration from macOS virtual machines to bare metal machines for iOS application builds. This transition significantly reduced build times (up to 75% for pre-merge checks) and improved stability by eliminating the performance variability inherent in shared VM environments and SAN storage. The team plans to further increase the adoption of bare metal machines and eventually replace the legacy Xcode build system with Bazel.

All Spotify trails
  1. How We Gave Superpowers to Our macOS CIThis post details the technical decision-making and implementation of migrating macOS CI agents from virtual machines to bare metal. It outlines the performance issues with VMs (variance in build times, I/O bottlenecks due to high write usage on SAN) and the benefits observed with bare metal (consistent build times, twice as fast builds, improved stability). The post includes benchmark data comparing VM and bare metal performance for iOS client release builds and unit testing configurations, highlighting P50 decreases from over 16 minutes to less than 8 minutes for App Store builds. It also mentions the use of Flow Swiss as a bare metal provider and the integration with existing tooling.
  2. Shaving off 50% waiting time from the iOS Edit-Build-Test cycleThis post details specific build settings and compiler flags that can significantly reduce iOS build times during development. It identifies 'DWARF' instead of 'DWARF with dSYM File' for Debug Information Format and using '-O3' instead of '-O4' (which enables Link Time Optimizations) as key optimizations. The author explains the technical reasons behind these improvements, focusing on the linking and dSYM generation stages of the build process.