Detection
migetpacks detects Bun when any of these signals are present:
| Priority | Signal |
|---|
| 1 | bun.lock or bun.lockb (lockfiles) |
| 2 | bunfig.toml (config file) |
| 3 | .bun-version (version file) |
| 4 | bun-types in package.json dependencies |
Bun detection runs after backend frameworks (Ruby, Python, Go, etc.) but before Node.js. If your project has both a bun.lock and a Gemfile, it will be detected as Ruby with Bun available as a secondary buildpack.
Version Detection
Bun version is resolved in this order:
| Priority | Source | Example |
|---|
| 1 | BUN_VERSION env var | BUN_VERSION=1.3.4 |
| 2 | .bun-version file | 1.3.4 |
| 3 | version in bunfig.toml | version = "1.3.4" |
| 4 | Default | 1.3.4 |
Build Process
migetpacks generates a multi-stage Dockerfile optimized for Bun:
# Builder stage
FROM oven/bun:1.3.4 AS builder
WORKDIR /build
# Layer 1: Copy dependency files (cached if lockfile unchanged)
COPY package.json bun.lock ./
# Layer 2: Install dependencies
RUN bun install
# Layer 3: Copy source code
COPY . .
# Layer 4: Run build script (if present)
RUN bun run build
# Runtime stage
FROM oven/bun:1.3.4-slim
WORKDIR /app
COPY --from=builder /build /app
Entry Point Detection
The entry point is automatically detected in this order:
.ts/.js file referenced in scripts.start of package.json- Common file patterns:
index.ts, server.ts, app.ts, main.ts, src/index.ts, src/server.ts, index.js, server.js
- Falls back to
index.ts
Build Script
If package.json contains a "build" script, bun run build is automatically executed after dependency installation. You can override this with the BUILD_COMMAND environment variable.
Bun supports two lockfile formats:
bun.lock (text-based, newer format)bun.lockb (binary, legacy format)
Both are automatically detected and copied during the build.
Run Command
The default run command is determined in this order:
| Priority | Source | Command |
|---|
| 1 | RUN_COMMAND env var | User-specified |
| 2 | web: in Procfile | From Procfile |
| 3 | Default | bun run {entrypoint} |
Caching
Docker Layer Caching
Dependencies are installed in a separate layer before source code is copied. bun install is only re-run when package.json or bun.lock/bun.lockb changes.
BuildKit Cache Mounts
When BUILD_CACHE_DIR is configured, BuildKit cache mounts are used:
| Cache Path | Contents |
|---|
/cache/bun | Bun install cache (~/.bun/install/cache) |
Registry Cache
Use CACHE_IMAGE to push/pull BuildKit inline cache layers to a registry for cross-build caching.
DHI Support
Bun is supported with Docker Hardened Images (requires version 1.3.6 or later).
| Stage | Image |
|---|
| Build | dhi.io/bun:{version}-dev |
| Runtime | dhi.io/bun:{version} |
DHI images for Bun are only available starting from version 1.3.6. If your project uses an older version, migetpacks will fall back to the standard oven/bun images.
-dev variant includes a shell for building. The runtime image is distroless with no shell, providing a minimal attack surface.
Example
docker run --rm \
-v /path/to/app:/workspace/source \
-v /var/run/docker.sock:/var/run/docker.sock \
-e OUTPUT_IMAGE=my-bun-app:latest \
miget/migetpacks:latest
With Custom Options
docker run --rm \
-v /path/to/app:/workspace/source \
-v /var/run/docker.sock:/var/run/docker.sock \
-e OUTPUT_IMAGE=registry.io/app:v1 \
-e BUN_VERSION=1.3.4 \
-e BUILD_COMMAND="bun run build:prod" \
-e USE_DHI=true \
miget/migetpacks:latest
