vanshikamunjal665-containerization-theory.github.io

CONTAINERIZATION AND DEVOPS THEORY

10 FEBRUARY 2026

MULTISTAGE DOCKERFILES

Reference Link:
https://upessocs.github.io/#dir=/Lectures/Containerization%20and%20DevOps/Theory/&file=019%20Multistage%20Dockerfiles%20Best%20Practices%20size,%20speed%20and%20security.md

Screenshots of commands

C Hello World Code
Image

Dockerfile (Multistage)
Image

Image

Image

1. Enter wsl

wsl

2. Changing directory

cd "/mnt/c/Users/Vanshika Munjal/Desktop/Containerization-Theory/class-task-6Feb"

3. Building image from Dockerfile

docker build -t c-app:1.0 .

docker build → build an image from a Dockerfile
-t c-app:1.0 → tag the image
c-app = image name
1.0 = version
. → current directory contains the Dockerfile
So Docker looks for a file named Dockerfile in this folder.

4. Starting container

docker run -it c-app:1.0

Container starts CMD [”./hello”] executes

5. List all Docker images present on the system

docker images

Dockerfile Code Explanation

FROM ubuntu:22.04 AS builder Uses Ubuntu 22.04 as the base image and names this stage builder for compiling the program.

RUN apt-get update && apt-get install -y gcc Updates package lists and installs the GCC compiler inside the container.

COPY hello.c . Copies the C source file from the host system into the container.

RUN gcc -static -o hello hello.c Compiles the C program into a statically linked executable named hello.

FROM scratch Starts a new minimal image with no operating system or libraries.

COPY --from=builder /hello /hello Copies only the compiled binary from the builder stage into the final image.

CMD ["./hello"] Specifies the default command to run the C program when the container starts.

Conclusion

The Docker image is very small because a multi-stage build is used where the C program is compiled in a separate builder stage and only the final compiled binary is copied into the runtime image. The final image uses scratch as the base image, which contains no operating system, no libraries, and no package manager. Additionally, the C program is compiled as a statically linked binary, so it does not require any external runtime dependencies. As a result, the final image contains only a single executable file, making the image size extremely small (less than 1 MB).