DOCKER
101
Ship your machine, not your excuses.
The death of “but it works on my machine.” 🐳
Hi, I'm Amdadul Bari 👋
DevOps & Platform Engineer. My actual job: make sure code that works on one machine works on ten thousand.
I build platforms that let teams ship with confidence — because “great infrastructure should be invisible.”
…and it all started with an app that only ran on my laptop — just like yours. 😄
I collect these like cargo. 📦
Every one of these started exactly where you are tonight. The path is real — and reachable. 🧗
Where this ship is sailing ⛴️
This is interactive — shout answers, laugh at the memes, ask anything. By the end, you'll containerize your own project.
“It works on my machine.” 🤷
It has killed demos, delayed launches, and started 30 years of war between developers and ops. Everyone has said it. Today, we kill it. 💀
Same code. Four disasters. 🎬
4 laptops · 4 operating systems · 3 versions of Python · 1 deadline in 6 hours. Not a bug — a horror movie.
Your code isn't alone.
It has ghosts.
Your app secretly leans on a hundred invisible things that just happen to live on your laptop. Clean machine → ghosts gone → app dies.
- 🐍Python 2.7 AND 3.9 AND 3.11 — nobody knows which one runs
- 📦node_modules heavier than a small galaxy
- 🕯️A library you installed at 3 a.m. in 2022 — everything depends on it
- 🌫️Your PATH: a mystery not even you understand
- 🗂️final_project_v2_real_FINAL.zip
You ship the tip. The rest sinks you. 🧊
Everything below came “for free” on your laptop. The fix isn't “be careful” — ship the whole iceberg. 🚢
Devs threw code over the wall 🧱
“It works! Ship it!” throws code over the wall →
Nobody could reproduce anyone's setup. Endless blame.
“…it doesn't run here.” 3 a.m. pages. Sadness.
In 2013 a little whale showed up and knocked the wall down.
You: “It only works on my machine.”
Docker: “Cool. We'll ship your machine.” 🚢
Seal the code + its entire haunted environment into one box — and run that exact box anywhere on Earth.
So… what is Docker?
Docker is a tool that packs your app into a container — a sealed box that runs identically everywhere: your laptop, your friend's, a server, the cloud.
A container = a tiffin box for code.
Mom packs the food, the exact spices, the right rice — and seals it. Open it in the hostel, in class, on the bus: same taste, every time.
- 🍱Seals your code + libraries + settings in one box
- 🌍Open it anywhere — identical every time
- ⚡Boots in seconds, lighter than you'd guess
Why not just use a whole computer? 🖥️
Virtual Machine
Renting a whole apartment — kitchen, bathroom, the works — for one houseplant.
Container
Just the shelf. Borrows the building's plumbing (your OS).
Your laptop runs 50 containers for breakfast — but 2 VMs and it starts sweating. 🥵
Why is a container so tiny & fast?
Carries its own entire operating system. That's the gigabytes.
Shares the building's kitchen & plumbing (the host OS kernel).
…what's unique to your app. Starts instantly, weighs almost nothing.
Shared plumbing = cheaper, lighter, faster. That's the whole trick. 🔧
Image → Container → Registry
One recipe → cook endless identical dishes → share it with the planet. 🌐
An image is a stacked sandwich
Built bottom-up in layers. The magic: layers are cached and shared.
- 🍞Change only your code? Docker reuses every layer below
- ⚡So the 2nd build takes seconds, not minutes
- 💾Ten apps on the same base? They share that layer on disk
6 lines. The whole recipe. 👩🍳
A Dockerfile is a to-do list for Docker, read top to bottom. That's it.
- FROM“Start from a mini Python computer”
- RUN“Install my libraries”
- COPY“Bring my code in”
- CMD“Now run it 🙏”
FROM python:3.12-slim # a mini computer WORKDIR /app # go to my folder COPY requirements.txt . RUN pip install -r requirements.txt COPY . . # bring my code CMD ["python", "app.py"] # please work 🙏
docker build — freeze the recipe
docker build -t myapp . -t myapp → name it "myapp" . → recipe is in THIS folder ✔ Step 1/6 : FROM python:3.12-slim ✔ Successfully built & tagged myapp:latest 🍰
One command turned your messy project into a portable, frozen image.
docker run — bring it to life
docker run myapp ✔ Running on http://localhost:8000 ✔ …exactly the same on EVERY machine 🌍
Your laptop · Rakib's · the cursed lab PC · a server in Singapore — identical. “Works on my machine” is now physically impossible.
“I ran it… why is my browser empty?”
A container is a sealed room — by default, no doors. The -p flag installs one.
- 🚪-p 8000:8000 = connect your laptop's port → the container's port
- 🌐Now localhost:8000 actually opens your app
- 🧠Forgot -p? App runs fine — you just can't reach it
docker run -p 8000:8000 myapp └──┬──┘ your laptop : container ✔ open http://localhost:8000 🎉
Four commands you'll use forever
Lists your live containers right now.
Read output & crash reasons. You'll live here.
Open a shell inside the running box.
Politely stop the container.
90% of debugging is just reading the logs. Befriend docker logs early. 🤝
Containers are disposable. Your data isn't.
Delete a container and everything inside vanishes — on purpose. So where does your database live?
- 🧹Container = a whiteboard — wiped when you leave
- 📓Volume = your notebook — a folder that survives, plugged in from outside
- 📌Rule of thumb: code in the image, data in a volume
docker run -v mydata:/var/lib/db \ postgres # -v mydata → a notebook that # OUTLIVES the container 📓 ✔ delete container → data is safe
Like GitHub — but for whole apps.
Docker Hub is the world's shelf of ready-made containers. push yours up, pull anyone's down.
- ⬆️docker push — upload your image for anyone to run
- ⬇️docker pull postgres — a full database, zero install
- 🎁Your friend runs your app with one pull. No setup. Ever.
docker push amdadul/myapp ✔ pushed to Docker Hub 🌍 # now, anyone, anywhere: docker run amdadul/myapp ✔ it just… works. ✨
Real apps travel in a squad. 👥
docker compose = one file for the whole gang (app + database + cache), one command to launch them all, already wired together.
Teammate clones → runs one command → gets your exact setup, database and all. The dream. 😌
services: app: build: . ports: ["8000:8000"] db: image: postgres:16 docker compose up # launches EVERYTHING 🚀
Mistakes you'll make (then never again)
You COPY'd node_modules, .git & cat photos. Add a .dockerignore.
App runs, browser empty, you panic. Open the door.
Deleted the container, forgot the volume. RIP database.
“latest” silently changed. Pin real versions: :3.12.
Every single one of us shipped a 2GB image once. It's a rite of passage. 🎓
The container is a doorway. 🚪
Once your app is a container, the whole cloud-native world opens up — and it all sits on top of what you just learned.
Runs thousands of containers & auto-heals crashes at 3am.
Robots build & ship your container on every git push.
Run your container at planet scale — AWS, GCP, Azure.
You didn't learn a tool today. You learned the foundation of the whole industry.
This is your unfair advantage. 🎯
“Docker” on a CV = instant green flag for internships.
Your project runs on the professor's PC. Every time.
K8s, CI/CD, cloud jobs — all built on containers.
The basics? Honestly, one focused weekend.
Docker is the #1 skill in DevOps internship posts. You're one weekend from your CV. 🚀
4 tiny steps. Do them this week.
Docker Desktop. 10 min, one download.
Add a Dockerfile to a project you already have.
build + run. Feel the “aha.”
Push to Docker Hub. Send a friend one command.
The entire talk, on one card
docker build -t myapp . # bake the image 🍰 docker run -p 8000:8000 myapp # run + open the door 🚪 docker ps # what's running? 👀 docker logs <id> # why did it break? 📜 docker push amdadul/myapp # share with the world 🌍 docker compose up # launch the whole squad 🚀
Six commands. That's genuinely enough to be dangerous. 😎
If you forget everything else…
“Works on my machine” — your app dragged invisible ghosts.
A container seals code + environment into one portable box.
Build → run → share → and the whole cloud opens up.
Don't ship your code and pray. Ship the whole box. 🐳
From “works on my machine”
to “works on every machine.”
Thank you, Jatiya Kabi Kazi Nazrul Islam University! 🙌
Now go ship something. Questions? Let's talk — and DM me anytime.
Q & A
Ask me anything — Docker, DevOps, Kubernetes, certs, careers, or how I ruined a production server once. 😅