Custom Dockerfile

Overview

migetpacks prioritizes its optimized multi-stage builds for known languages. A Dockerfile in your project is only used as a fallback when no supported language is detected. To force migetpacks to use your Dockerfile, set LANGUAGE=dockerfile or DOCKERFILE_PATH.

Detection Priority

Explicit override (DOCKERFILE_PATH or LANGUAGE=dockerfile)

If DOCKERFILE_PATH is set, or LANGUAGE=dockerfile is specified, your Dockerfile is used immediately.

Language detection

migetpacks checks for supported languages (Ruby, Python, Go, Node.js, etc.) and generates an optimized build.

Dockerfile fallback

Only if no supported language is detected, migetpacks falls back to using Dockerfile in your project root.

This priority order ensures you get migetpacks’ optimized builds by default. If your project has both package.json and Dockerfile, migetpacks will detect Node.js and generate its own Dockerfile. Use LANGUAGE=dockerfile to override this behavior.

Using DOCKERFILE_PATH

Point to a specific Dockerfile when it is not in the default location:

docker run --rm \
  -v /path/to/app:/workspace/source:ro \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -e OUTPUT_IMAGE=registry.io/my-app:latest \
  -e DOCKERFILE_PATH=docker/Dockerfile.prod \
  miget/migetpacks:latest

DOCKERFILE_PATH is relative to the project root (or PROJECT_PATH if set). You can also use an absolute path.

Examples

Standard Dockerfile in Root

If your project has a Dockerfile in the root directory, no extra configuration is needed:

my-app/
├── Dockerfile        # Used automatically
├── src/
├── package.json
└── ...

docker run --rm \
  -v /path/to/my-app:/workspace/source:ro \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -e OUTPUT_IMAGE=registry.io/my-app:latest \
  miget/migetpacks:latest

Multiple Dockerfiles

Projects with environment-specific Dockerfiles:

my-app/
├── docker/
│   ├── Dockerfile.dev
│   ├── Dockerfile.prod
│   └── Dockerfile.test
├── src/
└── ...

docker run --rm \
  -v /path/to/my-app:/workspace/source:ro \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -e OUTPUT_IMAGE=registry.io/my-app:latest \
  -e DOCKERFILE_PATH=docker/Dockerfile.prod \
  miget/migetpacks:latest

docker run --rm \
  -v /path/to/my-app:/workspace/source:ro \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -e OUTPUT_IMAGE=my-app:dev \
  -e DOCKERFILE_PATH=docker/Dockerfile.dev \
  miget/migetpacks:latest

Monorepo with Custom Dockerfile

Combine PROJECT_PATH and DOCKERFILE_PATH:

docker run --rm \
  -v /path/to/monorepo:/workspace/source:ro \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -e OUTPUT_IMAGE=registry.io/my-service:latest \
  -e PROJECT_PATH=services/api \
  -e DOCKERFILE_PATH=Dockerfile.production \
  miget/migetpacks:latest

This looks for the Dockerfile at services/api/Dockerfile.production.

Use Cases

Custom Base Images

When you need a specific base image not supported by migetpacks:

FROM my-internal-registry.io/custom-base:latest

WORKDIR /app
COPY . .
RUN make build

EXPOSE 8080
CMD ["./my-app"]

If the base image lives in a private registry, set EXTERNAL_REGISTRY_URL / EXTERNAL_REGISTRY_USERNAME / EXTERNAL_REGISTRY_PASSWORD on the build so the builder can authenticate before pulling.

Complex Multi-Stage Builds

When your build process requires custom stages:

FROM node:20 AS frontend
WORKDIR /frontend
COPY frontend/package*.json ./
RUN npm ci
COPY frontend/ .
RUN npm run build

FROM golang:1.22 AS backend
WORKDIR /backend
COPY go.* ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 go build -o /app

FROM gcr.io/distroless/static-debian12
COPY --from=backend /app /app
COPY --from=frontend /frontend/dist /static
EXPOSE 8080
CMD ["/app"]

Specific Optimization Needs

When you need fine-grained control over layer ordering, build arguments, or caching:

FROM python:3.12-slim AS builder

ARG PIP_INDEX_URL
WORKDIR /app

# Install system dependencies
RUN apt-get update && apt-get install -y --no-install-recommends \
    libpq-dev gcc && rm -rf /var/lib/apt/lists/*

# Layer-cached dependency install
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

COPY . .

FROM python:3.12-slim
COPY --from=builder /usr/local/lib/python3.12/site-packages /usr/local/lib/python3.12/site-packages
COPY --from=builder /app /app
WORKDIR /app
EXPOSE 5000
CMD ["python", "app.py"]

Build Caching with Custom Dockerfiles

Registry-based caching (CACHE_IMAGE) works with custom Dockerfiles:

docker run --rm \
  -v /path/to/app:/workspace/source:ro \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -e OUTPUT_IMAGE=registry.io/my-app:latest \
  -e DOCKERFILE_PATH=Dockerfile \
  -e CACHE_IMAGE=registry.io/my-app:buildcache \
  -e CACHE_MODE=max \
  miget/migetpacks:latest

BUILD_CACHE_DIR and language-specific BuildKit cache mounts are only available in auto-generated Dockerfiles. If you use a custom Dockerfile, you must manage cache mounts yourself.

What migetpacks Still Provides

Even when using a custom Dockerfile, migetpacks handles:

Building the image with BuildKit
Pushing to the target registry (OUTPUT_IMAGE)
Registry-based caching (CACHE_IMAGE)
Architecture targeting (ARCH)
Registry mirror configuration (REGISTRY_MIRROR)
Result file generation (RESULT_FILE)
Port detection from the built image

Getting Started

Guides

Configuration

Languages

Deploying

Reference

Overview

Detection Priority

Using DOCKERFILE_PATH

Examples

Standard Dockerfile in Root

Multiple Dockerfiles

Monorepo with Custom Dockerfile

Use Cases

Custom Base Images

Complex Multi-Stage Builds

Specific Optimization Needs

Build Caching with Custom Dockerfiles

What migetpacks Still Provides

​Overview

​Detection Priority

​Using DOCKERFILE_PATH

​Examples

​Standard Dockerfile in Root

​Multiple Dockerfiles

​Monorepo with Custom Dockerfile

​Use Cases

​Custom Base Images

​Complex Multi-Stage Builds

​Specific Optimization Needs

​Build Caching with Custom Dockerfiles

​What migetpacks Still Provides

Overview

Detection Priority

Using DOCKERFILE_PATH

Examples

Standard Dockerfile in Root

Multiple Dockerfiles

Monorepo with Custom Dockerfile

Use Cases

Custom Base Images

Complex Multi-Stage Builds

Specific Optimization Needs

Build Caching with Custom Dockerfiles

What migetpacks Still Provides