Bazel iOS builds on Limrun RBE

Build Bazel Apple projects on Limrun's remote Mac workers — from any environment (Linux, Windows, macOS, VM, container), no local Xcode.

lim xcode rbe

brings up a remote RBE stack, tunnels it to a local port, and writes a

.limrun/

config so

bazelisk build --config=limrun

runs Apple actions remotely. Never fall back to local Xcode or build tools.

Auth and CLI

Install if needed:

npm install --global lim

. Auth is

lim login

LIM_API_KEY

(may be set outside the project — don't ask for it just because it's absent). The CLI is the source of truth: the commands in this skill are verified, but if a flag errors or you need one not shown here, check

lim xcode rbe --help

instead of guessing.

Build

From the Bazel workspace root (has
```
MODULE.bazel
```
/
```
WORKSPACE
```
), run
```
lim xcode rbe
```
. It sets up the instance +
```
.limrun/
```
config and prints the exact build command. The tunnel runs in the background (prints a PID);
```
--no-daemon
```
keeps it foreground.

Run the printed command, e.g.

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

Don't hand-write

.limrun/

or the flags — the CLI generates them for the fleet's Xcode and your OS. Re-run

lim xcode rbe

(after

--stop

) to refresh after a fleet Xcode upgrade.

To add your own Bazel flags to the limrun path without editing the generated config, put them in user.limrun.bazelrc
at the workspace root. The generated config try-imports it last, so your

build:limrun --…

lines win, and it survives

lim xcode rbe

regeneration (

.limrun/

does not).

Run on a simulator

lim xcode rbe

is build-only; attach a simulator when the user wants to see or run the app. Check or attach (it installs the last build immediately, so no rebuild is needed):

bash

lim xcode get             # is a simulator already attached?
lim ios create --attach   # attach one

If the attach output includes a signed stream URL, share it with the user as a Markdown link, such as Live simulator.

With a simulator attached, every successful

--config=limrun

build automatically reinstalls and relaunches the app, no separate install step:

bash

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

Notes:

Attach upfront if you already know you want a sim:
```
lim xcode rbe --ios
```
(attaches at startup, removed on
```
--stop
```
).
Auto-install happens server-side from the build's events; there is no
```
lim xcode rbe install
```
subcommand or
```
--target
```
flag. To force a reinstall, rebuild (a cache-hit rebuild is seconds).
It fires when the successful invocation produced a single app, so in a multi-app workspace build one app target per invocation (
```
//App
```
, not
```
//...
```
); a multi-app build succeeds but installs nothing.

To tap, type, read the element tree, screenshot, or record the running app, switch to the limrun-ios-simulator
skill.

Upload builds as assets

To publish a build as a Limrun asset (preview links, installing on other simulators, CI artifacts), arm uploads at tunnel start or upload one build after the fact:

bash

lim xcode rbe --auto-upload preview/my-app --upload-ttl 24h  # every successful build refreshes the asset
lim xcode rbe upload preview/my-app --ttl 24h                # one-shot: the newest successful build

```
--auto-upload
```
holds for the tunnel's lifetime: each successful
```
--config=limrun
```
build re-uploads the app under that asset name, no post-build step. Upload results land in
```
.limrun/rbe.log
```
.
```
rbe upload
```
runs from the workspace root and needs a background tunnel plus at least one successful build; it errors otherwise.
TTLs are Go durations (
```
24h
```
,
```
30m
```
;
```
1d
```
is invalid) and optional.
To change the
```
--auto-upload
```
config of a running tunnel,
```
--stop
```
and re-run; the CLI refuses a mismatched re-arm instead of silently ignoring it.

Preview an uploaded app in a browser at

https://console.limrun.com/preview?asset=<name>&platform=ios

Teardown

Stop with lim xcode rbe --stop
(~20s to tear the remote stack down) and delete the instance with lim xcode delete <id>

Gotchas

Always pass
--digest_function=sha256
before
build
(use the command the CLI prints verbatim). The Limrun cache is SHA256-only; Bazel 9 defaults to BLAKE3. It's a startup flag, so it can't live in
```
--config=limrun
```
. Symptoms: build →
```
Cannot use hash function BLAKE3 with remote cache
```
; install →
```
non-SHA256 digest … rebuild with --digest_function=sha256
```
.
Run
lim xcode rbe
from the workspace root, not a subdirectory — it writes
```
.limrun/
```
there and fails fast otherwise.
A green build doesn't prove remote execution — cache hits (
```
action cache hit
```
/
```
remote cache hit
```
) make builds pass even with the tunnel gone. To force and verify real remote execution, see
```
references/verify-remote.md
```
.
The printed
.ipa
path won't exist on your machine — the build command carries
```
--remote_download_outputs=minimal
```
, which keeps the artifact in the instance's cache and downloads nothing. Bazel still prints its usual
```
Target //App:App up-to-date: …/App.ipa
```
line, but that file is not on disk. This is expected, not a failed build. With a simulator attached, the build auto-installs from the artifact's cache digest (read from the build event log, not the local file). Only if you genuinely need the
```
.ipa
```
locally, drop
```
--remote_download_outputs=minimal
```
from the build command and Bazel downloads the top-level output; auto-install keeps working either way.
A fresh instance can fail the first build with
Lost inputs no longer available remotely
(e.g.
```
… Assets.car
```
). It's a transient cache eviction between instances, not a code error; Bazel prints
```
Found transient remote cache error, retrying the build...
```
and the retry succeeds. To avoid hitting it mid-demo, pre-warm with a full build right after
```
lim xcode rbe
```
.
You don't have permission to save … in "CoreSimulator"
(actool/ibtool) is a fleet-side device gap, not your config. Retry; if it persists, report it to Limrun.
The project's own Bazel settings can fight RBE (Xcode pinned via a Starlark transition, custom
```
remote_default_exec_properties
```
, sandbox-hostile genrules). These are per-project, not Limrun bugs — walk
```
references/project-compatibility.md
```
before concluding RBE is broken.

limrun-xcode-bazel

NPX Install

Tags

SKILL.md Content

Bazel iOS builds on Limrun RBE

Auth and CLI

Build

Run on a simulator

Upload builds as assets

Teardown

Gotchas