A multi-stage build in Docker is a technique that allows you to create more efficient Docker images by using multiple stages in the build process. This approach enables you to separate the build environment from the final production environment, resulting in smaller and cleaner images.
In a multi-stage build, you typically have two or more FROM statements in your Dockerfile. The first stage is used to compile or build your application, including all necessary dependencies and tools. The subsequent stages copy only the necessary artifacts (like compiled binaries) from the previous stages, excluding any build tools or unnecessary files.
This results in a final image that contains only the essential components needed to run the application, which reduces the image size and improves security by minimizing the attack surface.
Example of a Multi-Stage Build
Here’s a simple example of a multi-stage build for a Node.js application:
# Stage 1: Build the application
FROM node:14-alpine AS builder
WORKDIR /app
COPY . ./
RUN npm install
# Stage 2: Create the final image
FROM node:14-alpine
WORKDIR /app
COPY --from=builder /app/ .
EXPOSE 3000
CMD [ "npm", "start" ]In this example:
- The first stage (
builder) installs dependencies and builds the application. - The second stage creates a final image that only includes the built application, resulting in a smaller image size.
