Expo and React Native: the Docker exception

· Tech

TLDR: Expo cannot run in Docker. iOS Simulator needs direct access to Metro bundler on the host. This is fine because Expo only uses public EXPO_PUBLIC_* vars. Real secrets live in the API container. For EAS Build, inject secrets with infisical run -- eas build.

Why Expo must run on the host

The iOS Simulator is a native macOS process. It needs direct access to Metro bundler. Expo Go on a physical device needs the dev server over your local network. Neither works when Metro is inside a container.

Why this is safe

Expo’s EXPO_PUBLIC_* variables are public by definition. They get bundled into the JavaScript and shipped to the client. They are not secrets.

Terminal window
# Expo on host, only public vars
cd apps/mobile
EXPO_PUBLIC_API_URL=http://localhost:3333 npx expo start

Real secrets (Stripe server keys, push notification tokens) live in the API container. The mobile app calls the API. It never sees secrets directly.

EAS Build

Inject build-time secrets only during the build command:

Terminal window
infisical run --env=staging -- eas build --platform ios --profile preview

.claudeignore for Expo

apps/mobile/.expo/
apps/mobile/ios/
apps/mobile/android/
*.mobileprovision
*.p12
*.keystore
GoogleService-Info.plist
google-services.json

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