- Split by toolchain — Linux owns containers and fast tests; macOS owns anything that touches code signing, notarization,
xcodebuild, or Simulator. - Parallelism shortens queues first — it does not linearly speed a single job when Apple services throttle uploads.
- Co-locate cache with runners — keep Git LFS, DerivedData keys, and object storage in the same region as your macOS fleet.
Why Linux Runs the Pipeline and Mac Only Relays
Dockerized unit tests and lint stay on Linux for cost and density. The moment a job needs a valid signing identity, notarized binaries, xcodebuild, UI tests in Simulator, or TestFlight promotion, you must enqueue a macOS runner. Linux stages source archives and deterministic cache keys; the Mac stage pulls deltas and emits signed artifacts back to your artifact store. For how RTT splits SSH batch work from interactive Xcode, see
remote Mac latency and parallel FAQ for JP/KR/HK/SG and US West.
Choosing Among Japan, Korea, Hong Kong, Singapore, and US West
Japan and Korea favor East Asia collaboration and fleets that ship localized apps. Hong Kong and Singapore balance Greater China RTT with strong regional peering. US West aligns with North American cloud egress, large IPA uploads, and CDN-adjacent distribution. The table below summarizes relay fit rather than raw map distance — always validate with traceroute from your office VPN.
| Region | Typical strength | Linux → Mac relay focus |
|---|---|---|
| Japan / Korea | East Asia coordination, multi-market releases | Measure RTT before naming a primary runner |
| Hong Kong / Singapore | Friendly RTT across Greater China | Interactive Xcode plus mid-size repo parallelism |
| US West | Same-region cloud upload and global backbone | Heavy builds; pair with Asia for desktop if RTT spikes |
Before you parallelize, name the bottleneck
Adding two M4 boxes mainly cuts queue wait; it rarely doubles throughput on a single sequential notarization gate. When App Store Connect or notary services rate-limit, merge steps, stagger uploads, and backoff retries instead of blindly fanning out identical jobs. Scale shards only after compile or Simulator fan-out is proven dominant, and pin Pods, SwiftPM, and DerivedData caches in the same account and region as the runner.
Memory and disk: when to parallelize versus upsize
M4 16GB covers CLI builds, lightweight Fastlane lanes, and modest Swift modules. 24GB fits medium Swift targets with a small Simulator slice. M4 Pro brings higher memory bandwidth for Simulator matrices and heavier Metal workloads. Plan for roughly 1TB when you keep multiple Xcode versions online; step to 2TB for monorepos or long-lived DerivedData that you refuse to cold-start each night. Gateway-style agents that share the same host should size unified memory carefully; for install-path and concurrency notes on remote Mac, read OpenClaw install paths, Gateway troubleshooting, and remote Mac memory.
Operations checklist
If queue depth grows but jobs stay healthy, add a same-spec runner before you jump tiers. If you see OOM kills or Simulator thrash, move to 24GB or M4 Pro before adding a third box. When disk pressure triggers clean builds, upgrade storage to 2TB or enforce aggressive cache eviction. Cap notarization retries so a flaky Apple endpoint does not rerun the entire upstream Linux stage.
Tag each relay job with the runner region in your observability stack so you can prove whether latency spikes correlate with App Store Connect, cross-region artifact copy, or local CPU saturation — that single label saves hours when executives ask why release night slipped.
Parallel decision matrix (M4 tiers and storage)
| Scenario | Node / configuration |
|---|---|
CLI xcodebuild, many small repos |
Hong Kong or Singapore; two M4 16GB shards beat one 24GB sitting idle in queue |
| Notarization plus large IPA | US West M4 Pro + 1TB; optional Hong Kong runner for interactive debugging |
| Multi-Simulator matrix | Lowest measured RTT region; M4 Pro + 2TB for golden images and cached runtimes |
FAQ
Run the relay on Mac mini M4 with fewer surprises
Apple Silicon Mac mini systems give you native xcodebuild and Simulator without x86 emulation tax, unified memory bandwidth that keeps Swift type-checking responsive, and idle power near four watts for always-on CI. macOS layers Gatekeeper, System Integrity Protection, and FileVault on top of that hardware, which matters when runners sit unattended in a colo rack. The total cost of ownership often beats assembling Windows build farms plus Mac sidecars because one quiet box covers signing, notarization, and local reproduction. If you want Linux CI and the Apple ecosystem to stay aligned without building your own machine room, Mac mini M4 or M4 Pro hosted beside the regions you measured is the most cost-effective 2026 starting point — tap the card below to learn more.