Guides

Write Your First Dockerfile (Beginners)

By Ravindra Bagale, DevOps trainer · LinkedIn · Published: 30 September 2026 · Last updated: 30 September 2026

Read this guide in: English · मराठी · हिंदी

Why do we need a Dockerfile? Because there is a real problem between developers and operations. Developers have an index.html (or app) that looks fine on the laptop. Operations — the employee on the server side — asks how to run the same thing on EC2. Copying files is not enough; the server needs the runtime bits too. A Dockerfile is the shared recipe: docker build creates an image, docker run starts a container.

Friends, watch one file become a running site. Names come after the fight.

Language: English · मराठी · हिंदी

Why do we need a Dockerfile?

1. Developers need a repeatable “how this app runs.”
2. Operations on the server side needs the same description — not tribal knowledge.
3. Without a recipe, every host becomes a special snowflake.

Need Docker working (install Docker on EC2).

What does operations have to do with the Dockerfile?

1. Operations still SSHs, checks health, opens ports carefully.
2. They run a tagged image, not a mystery folder.
3. Developers update the Dockerfile; both trust myweb:1 as “what we shipped.”

What is the problem? Suppose we are…

Suppose we are building Instagram (like updates)

Suppose a tiny static status page must match what the mobile app expects. Developer emails HTML. Operations installs nginx by hand on EC2. Next week the steps are forgotten. Users see a blank page.

Suppose we are working at Netflix and we are giving updates

Suppose every microservice must ship as a known image tag. Without a Dockerfile, “build on my laptop” is not what production runs.

Suppose you are working in Infosys on a client project

Suppose the client operations team says: “Give us a Dockerfile and a tag — we will not accept a zip of files.” That is the shared contract.

How a Dockerfile answers that same fight

mkdir myweb && cd myweb
cat > index.html <<'EOF'
<!doctype html>
<html><body><h1>DevOps lab page</h1><p>Same bits on laptop and server</p></body></html>
EOF

cat > Dockerfile <<'EOF'
FROM nginx:alpine
COPY index.html /usr/share/nginx/html/index.html
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]
EOF

docker build -t myweb:1 .
docker run --rm -d -p 8080:80 --name myweb myweb:1
curl -s http://localhost:8080 | head
docker logs myweb
docker stop myweb

What each Dockerfile line means:

1. FROM — start from a known base image.
2. COPY — put your files into the image.
3. EXPOSE — documents port 80 (still map with -p at run).
4. CMD — process when the container starts.

Changed the HTML? Rebuild a new tag:

docker build -t myweb:2 .
docker run --rm -p 8080:80 myweb:2

Common errors — story pain then fix

Samajla ka? Why Dockerfile = shared recipe for developer and server-side operations; Instagram / Netflix / Infosys “suppose”; tag every build. Practise myweb:1 tonight.