Build with Bazel

If your iOS app builds with Bazel (rules_apple / rules_swift), you don't need to sync sources or run xcodebuild remotely. Limrun ships a Bazel remote build execution (RBE) backend: Bazel keeps running on your laptop or CI runner, and every Apple action (Swift compilation, asset catalogs, codesigning, bundling) executes on Limrun's Mac fleet. Linux, Windows, and macOS clients all work, and none of them needs Xcode installed.

The flow:

1. Start the RBE endpoint with lim xcode rbe. It provisions an Xcode sandbox, starts the remote execution stack on it, and bridges it to a local port.
2. Run the printed build command. Bazel sends actions through the tunnel; results land in the remote cache.
3. Run, upload, or preview the built app: auto-install it on an attached simulator, or publish it as an Asset Storage asset.

Quick start

From the root of your Bazel workspace (the directory with MODULE.bazel or WORKSPACE):

npm install --global lim
lim login   # or export LIM_API_KEY

lim xcode rbe

The command sets everything up and prints the exact build command for your workspace, for example:

bazelisk --digest_function=sha256 build --config=limrun //App

Run it. That's the whole loop: the tunnel keeps running in the background, so from here on you just build.

What lim xcode rbe did:

• Provisioned an Xcode sandbox (or reused your most recent one) and started the RBE stack on it.
• Opened a tunnel so the endpoint is reachable at grpc://127.0.0.1:8980 (change with --port).
• Generated a .limrun/ directory in your workspace with the --config=limrun Bazel configuration matched to the fleet's Xcode version, and wired a try-import into your .bazelrc.

Don't hand-edit .limrun/; it is regenerated on the next lim xcode rbe. To add your own flags to the Limrun build path, put them in user.limrun.bazelrc at the workspace root. The generated config imports it last, so your build:limrun --... lines win and survive regeneration.

Run it on a simulator

lim xcode rbe is build-only until you attach a simulator. Attach one at startup with --ios, or at any point later:

lim xcode rbe --ios      # attach at startup; torn down on --stop
# or later:
lim ios create --attach  # attach to the running RBE instance

With a simulator attached, every successful --config=limrun build auto-installs and relaunches the built app on it. There is no separate install step; attaching also installs the last successful build immediately.

Upload builds as assets

To publish builds to Asset Storage (for PR previews, installing on other simulators, or CI artifacts), arm uploads when you start the tunnel:

lim xcode rbe --auto-upload preview/my-app --upload-ttl 24h

Every successful build then refreshes the preview/my-app asset automatically, with no post-build step. Upload results are written to .limrun/rbe.log. To upload a single build after the fact instead:

lim xcode rbe upload preview/my-app --ttl 24h

TTLs are optional Go durations (24h, 30m). Anyone in your organization can then open the build in a browser at https://console.limrun.com/preview?asset=preview/my-app&platform=ios.

Use it in CI

The same two commands work in CI. Arm the upload at startup so the job needs no extra step after the build:

on:
  pull_request:
    types: [opened, synchronize, reopened]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: npm install --global lim
      - name: Build on Limrun RBE
        env:
          LIM_API_KEY: ${{ secrets.LIM_API_KEY }}
        run: |
          lim xcode rbe --auto-upload my-app-pr-${{ github.event.number }}
          bazelisk --digest_function=sha256 build --config=limrun //App
          lim xcode rbe --stop

For pull request previews with a comment on the PR, use limrun-inc/ios-preview-action instead: it detects a Bazel workspace automatically and does the build, upload, comment, and cleanup in one step. See Automatic PR Previews.

Teardown

lim xcode rbe --stop     # stops the tunnel and the remote stack (~20s)
lim xcode delete <id>    # delete the instance when you're done with it

Good to know

• The built .ipa doesn't land on your machine. The generated config carries --remote_download_outputs=minimal: Bazel prints its usual Target //App:App up-to-date: .../App.ipa line, but the artifact stays in the instance's cache, where auto-install and uploads read it from. If you genuinely need the file locally, add --remote_download_outputs=toplevel to the build command.
• Run lim xcode rbe from the workspace root, not a subdirectory; it writes .limrun/ there and fails fast otherwise.
• Re-run after fleet Xcode upgrades. The generated config pins the fleet's Xcode version; lim xcode rbe --stop followed by lim xcode rbe refreshes it.
• Changing --auto-upload needs a restart. The CLI refuses to re-arm a running tunnel with a different upload config rather than silently ignoring it; --stop and re-run.

Next steps