How I write a Dockerfile without copying random examples

A Dockerfile is a recipe for building an image. The clearer the recipe, the easier the container is to rebuild and debug.

The Dockerfile Builder tool gives me a safe place to test the idea before I put it into a script, server, or production workflow.

The simple mental model

A Dockerfile is a recipe for building an image. The clearer the recipe, the easier the container is to rebuild and debug.

I try to reduce the tool to one question: what input do I have, what output do I expect, and what would make the result unsafe or misleading?

Step 1: Choose a base image that matches the runtime

Choose a base image that matches the runtime.

Start with a small example first. A small example is easier to inspect than a real production-sized case.

Step 2: Set a working directory

Set a working directory.

Step 3: Copy dependency files first when possible

Copy dependency files first when possible.

Step 4: Install dependencies

Install dependencies.

Step 5: Copy the application code

Copy the application code.

Step 6: Expose the port only as documentation

Expose the port only as documentation.

Step 7: Set the command the container should run

Set the command the container should run.

My checklist

Before I trust the result, I check:

• Choose a base image that matches the runtime.
• Set a working directory.
• Copy dependency files first when possible.
• Install dependencies.
• Copy the application code.
• Expose the port only as documentation.
• Set the command the container should run.

The tool saves time, but the important part is still understanding the input and reviewing the output before using it somewhere important.