Question 1

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 instruction after it must run again regardless of whether anything relevant changed.

The dominant cause is copying source code before installing dependencies. Editing any file invalidates that copy, so the dependency install runs from scratch on every build even though the dependency list did not change. Copying only the manifest files, installing, and then copying the source means the expensive layer is reused until dependencies actually change. This single reordering is usually the largest improvement available.

The build context is the second common cause and is invisible until you look. Everything in the directory is sent to the daemon before the build starts, so a project containing a dependency directory, version control history or large assets can spend a long time transferring before any instruction runs. An ignore file fixes it, and the build output reports the context size, which makes the problem easy to confirm.

Other contributors are worth knowing. Running package manager updates in a separate instruction from installs means a cached update layer paired with a fresh install, which can fail as well as being slow. Combining them in one instruction is both faster and more correct.

Multi-stage builds help beyond image size, because independent stages can build in parallel with a modern builder.

For repeated builds in continuous integration, the cache usually does not persist between runs, which is why builds are fast locally and slow in the pipeline. Most platforms support exporting and importing a cache, or using a remote cache, and configuring that removes the difference.

Question 2

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

Question 3

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 4

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 5

What are some effective React performance optimization techniques?

Accepted Answer

Optimizing React performance involves techniques like code splitting, memoization, and lazy loading to enhance speed and responsiveness. Implement these methods based on your app's needs.

Question 6

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 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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