Dockerfile Basics: FROM, RUN, and CMD

🔥 𝐘𝐨𝐮𝐫 𝐀𝐩𝐩 𝐑𝐮𝐧𝐬 𝐋𝐨𝐜𝐚𝐥𝐥𝐲. 𝐍𝐨𝐰𝐡𝐞𝐫𝐞 𝐄𝐥𝐬𝐞. 𝐇𝐞𝐫𝐞'𝐬 𝐖𝐡𝐲. [Docker Deep Dive — Day 1/5] Your app works perfectly. Your teammate runs it. It crashes. Different OS. Different Python. Different everything. Docker fixes this with one file — the Dockerfile. Think of a shipyard blueprint. Write it once, any shipyard in the world builds the identical ship. The Dockerfile is that blueprint for your app. FROM picks your hull — the base OS and runtime. RUN installs your tools. COPY loads your code as cargo. CMD sets it sailing. dockerfile FROM python:3.11 RUN pip install flask COPY . /app CMD ["python", "app.py"] docker build reads the blueprint and creates a Docker image — your ship, frozen in dry dock. docker run launches it as a container — the live ship hitting open water. 𝐅𝐀𝐐: Q: Why is FROM always first? Every ship needs a hull before anything else. No FROM, nothing to build on. Q: What's the difference between RUN and CMD? RUN works in dry dock during build. CMD fires when the ship hits water at runtime. Q: Can FROM pull any language? Python, Java, .NET, Node — thousands of base images exist on Docker Hub. Pick your hull. Tomorrow: image vs container — what really happens when you delete one? #DevOps #Docker #Dockerfile #CloudEngineering #DockerDeepDive #DevOpsInterview

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