---
title: CI setup
description: Using kache in GitHub Actions and other CI environments.
---
# CI setup
## GitHub Actions
The fastest way to add kache to a GitHub Actions workflow is the official action:
```yaml title=".github/workflows/ci.yml"
steps:
- uses: actions/checkout@v4
- uses: dtolnay/rust-toolchain@stable
- uses: kunobi-ninja/kache-action@v1
- run: cargo build --release
```
The action installs kache, sets `RUSTC_WRAPPER=kache`, and persists the local kache store with GitHub's built-in Actions cache by default. No S3 bucket is required.
<Callout type="info">
The default GitHub Actions cache backend is the simplest choice for most open-source projects. For private infrastructure, larger caches, or sharing across repositories, use an S3 bucket instead.
</Callout>
## Using S3 with kache-action
If you have an S3 bucket, pass it to the action:
```yaml
steps:
- uses: actions/checkout@v4
- uses: dtolnay/rust-toolchain@stable
- uses: kunobi-ninja/kache-action@v1
with:
s3-bucket: my-build-cache
s3-region: eu-west-1
s3-access-key-id: ${{ secrets.S3_ACCESS_KEY_ID }}
s3-secret-access-key: ${{ secrets.S3_SECRET_ACCESS_KEY }}
- run: cargo build --release
- run: cargo test
```
For S3-compatible stores such as MinIO, Ceph, or R2, also set `s3-endpoint`:
```yaml
- uses: kunobi-ninja/kache-action@v1
with:
s3-bucket: my-build-cache
s3-endpoint: https://minio.internal:9000
s3-access-key-id: ${{ secrets.S3_ACCESS_KEY_ID }}
s3-secret-access-key: ${{ secrets.S3_SECRET_ACCESS_KEY }}
```
With S3 configured, the action starts the kache daemon for warm prefetch, saves a build manifest after the build, pushes new artifacts with `kache sync --push`, writes a job summary, and can post a sticky PR comment with `kache report --format github`.
Useful action inputs:
| Input | Default | Description |
|---|---|---|
| `version` | latest release | kache version to install |
| `github-cache` | `true` | Use GitHub Actions cache when S3 is not configured |
| `s3-bucket` | — | S3 bucket name; enables the S3 backend |
| `s3-region` | `us-east-1` | S3 region |
| `s3-prefix` | `artifacts` | S3 key prefix |
| `s3-endpoint` | — | Custom endpoint for MinIO, Ceph, R2, etc. |
| `sync` | `false` | With S3, pull the full remote cache during setup |
| `warm` | `true` | With S3, prefetch likely artifacts from the saved build manifest |
| `manifest-key` | target triple | Scope saved manifests for different build shapes |
| `pr-comment` | `true` | Post or update a sticky PR cache summary comment |
| `max-size` | `50GiB` | Local store cap, mapped to `KACHE_MAX_SIZE` |
## Other CI systems
Outside GitHub Actions, configure kache directly via environment variables:
```yaml
env:
RUSTC_WRAPPER: kache
KACHE_S3_BUCKET: my-build-cache
KACHE_S3_REGION: us-east-1
KACHE_S3_ACCESS_KEY: ${{ secrets.S3_ACCESS_KEY }}
KACHE_S3_SECRET_KEY: ${{ secrets.S3_SECRET_KEY }}
```
For AWS with IAM roles (OIDC), skip the access key variables and let kache use the standard credential chain.
For S3-compatible stores, also set `KACHE_S3_ENDPOINT`. `KACHE_S3_PREFIX` is optional and defaults to `artifacts`.
When no daemon is running in an ephemeral runner, use explicit sync steps:
```yaml
- name: Warm cache
run: kache sync --pull
- run: cargo build --release
- name: Push new artifacts
run: kache sync --push
if: always()
```
The `if: always()` on the push step stores newly built artifacts even when the build fails partway through. Partial cache population still speeds up future runs.
Both sync subcommands require a configured S3 remote. Without one they error with `No remote configured`. By default `kache sync --pull` is filtered to the crates in the current workspace's `Cargo.lock`, so an ephemeral runner only fetches what this build needs. Use `kache sync --pull --all` to pull every artifact in the bucket regardless of the local lockfile.
<Callout type="warn">
`kache sync` reports failed transfers as `(N failed)` on its progress line but still exits `0`, so CI cannot detect partial transfer failures from the exit code alone. If that matters, scan the step's stderr for `failed`.
</Callout>
## CI progress output
kache can print per-crate progress lines to stderr when `KACHE_PROGRESS` is set. It is silent by default — both in CI and locally — to avoid cargo caching the wrapper's stderr as stale compiler diagnostics. Set the variable to opt in:
| Value | Behavior |
|---|---|
| unset / anything else | Silent (default) |
| `1` or `hits` | Print hits only |
| `verbose` or `all` | Print hits, dups, and misses |
With `KACHE_PROGRESS=verbose`, lines look like:
```
[kache] serde: local hit (2ms, 1.2 MB)
[kache] tokio: local hit (3ms, 4.8 MB)
[kache] myapp: miss (1.4s, 892 KB)
```
At `hits`/`1` only the `local hit` lines appear; `miss` and `dup` lines show up only under `verbose`/`all`. The format is `[kache] <crate>: <label> (<elapsed>[, <size>])`. There is no terminal or CI detection — output depends solely on this variable.
## Coverage and instrumentation
Coverage tools like `cargo-tarpaulin` and `cargo-llvm-cov` use `-C instrument-coverage`, which changes what kache stores (path remapping is skipped to preserve source mapping for coverage reports). This produces different cache keys from regular builds, so the coverage cache is isolated automatically.
That said, many teams disable kache for coverage runs entirely to keep things simple:
```yaml
- name: Test with coverage
run: cargo tarpaulin --engine llvm --all-features --workspace --out Json
env:
RUSTC_WRAPPER: "" # disable kache for this step
```
## Disabling kache for specific steps
```yaml
- name: Some step without caching
run: cargo build
env:
KACHE_DISABLED: "1"
```
Only `1` or `true` (case-insensitive) disable kache. Other values — including `0`, `false`, and empty — are ignored, so to re-enable kache in a later step you must unset the variable rather than set it to `0`.
kache still strips the rustc `-C incremental=…` flags when disabled, which avoids APFS-related corruption in git worktrees on macOS — even when caching is off.