Question 1

Why is my Docker image so large and how do I shrink it?

Accepted Answer

Image size is the sum of every layer, and layers are immutable. That second point catches people out: deleting a file in a later instruction does not reclaim the space, because the earlier layer still contains it. An image that installs build tools and then removes them in a separate step is as large as if the removal never happened.

The three biggest wins, in rough order of impact, are these.

- Use a multi-stage build. Compile or install dependencies in one stage, then copy only the finished artifact into a clean final stage. Everything used to produce the output, including compilers and package caches, is discarded rather than shipped.
- Choose a smaller base. A full distribution image carries a complete userland you almost certainly do not need. Slim variants are dramatically smaller, and minimal ones smaller still, though the latter can complicate anything depending on standard C library behaviour.
- Combine related instructions and clean up within the same one. Installing packages and removing the package manager cache in a single instruction means the cache never becomes part of a committed layer.

A frequently overlooked cause is the build context itself. Without an ignore file, everything in the directory is sent to the daemon and can be copied in by a broad copy instruction, which is how dependency directories, version control history and local environment files end up inside images. Adding an ignore file is the cheapest possible fix and often the largest single saving.

Ordering affects build speed rather than size, but it is worth getting right at the same time. Copying dependency manifests and installing before copying source means editing your application does not invalidate the expensive install layer.

Question 2

Why is my Docker build so slow?

Accepted Answer

Most slow builds are slow because the cache is being invalidated unnecessarily, not because the work itself is expensive. Each instruction produces a layer, and once one is invalidated every

Question 3

What is the difference between a Docker image and a container?

Accepted Answer

An image is a static, read-only template. A container is a running, or stopped, instance created from one. The relationship is close to that between a program on disk and a process running it: one

Question 4

What is the difference between COPY and ADD in a Dockerfile?

Accepted Answer

Both instructions move files from the build context into the image, and for ordinary files they behave identically. The difference is that ADD has two extra behaviours that trigger automatically, and

Question 5

What is a build artifact, and why does reproducibility matter?

Accepted Answer

An artifact is the packaged output of a build — a compiled binary, a container image, a library archive — and reproducibility means that building the same source produces an identical artifact, every

Question 6

Why does my Docker container exit immediately after starting?

Accepted Answer

A container lives exactly as long as its main process. When the process started by the image's CMD or ENTRYPOINT finishes, the container stops, regardless of anything else running inside it. So an

Question 7

How to optimize React app performance?

Accepted Answer

Optimizing React app performance involves strategies like code splitting, memoization, lazy loading, and optimizing state management. These techniques enhance rendering speed and reduce resource consumption.

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