Docker multi-stage builds

Example of a multi-stage Dockerfile

You can use multi-stage builds in a single Dockerfile like so:

# ==============================================================================
# Stage: build
# ==============================================================================
# Use the golang image as a base
FROM golang:1.25 AS build

# Set working directory to src/
WORKDIR /src

# Copy a simple Go program to main.go
COPY <<EOF ./main.go
package main

import "fmt"

func main() {
  fmt.Println("hello, world")
}
EOF

# Compile main.go into a binary at /bin/hello
RUN go build -o /bin/hello ./main.go


# ==============================================================================
# Stage: main
# ==============================================================================
FROM scratch

COPY --from=build /bin/hello /bin/hello

CMD ["/bin/hello"]

We have two stages in the above Dockerfile:

1. build
2. main

The build stage creates a /bin/hello binary.

The main stage copies the /bin/hello binary from the build stage to bin/hello and then executes it.

Stop at a specific build stage

You can also build an image upto a specific stage:

docker build --target build -t hello .

Running the command above will create an image with all artifacts from the build stage only. This can be useful for:

• Debugging a specific build stage
• If you want a base stage and a development stage where the latter adds additional development tools like XDebug for PHP..

Copy artifacts from an external image

COPY --from=nginx:latest /etc/nginx/nginx.conf /nginx.conf

Links

• Multi-stage builds – DockerHub