5 Docker Build

docker build is the command that reads a Dockerfile and a build context, executes each instruction in sequence, and produces a new image as the result, serving as the primary entry point for turning a Dockerfile's declarative instructions into an actual, usable artifact.

Basic Usage

The most basic invocation specifies a build context (a directory) and, optionally, a tag for the resulting image.

docker build -t myapp:1.0 .

The . here specifies the current directory as the build context; Docker looks for a file named Dockerfile within it by default.

Specifying a Different Dockerfile

A different file name or location can be specified explicitly, useful for projects maintaining multiple Dockerfiles for different purposes.

docker build -f Dockerfile.production -t myapp:prod .

Passing Build Arguments

Values declared with ARG in the Dockerfile can be supplied at build time through --build-arg.

docker build --build-arg NODE_VERSION=20 -t myapp .

Building Without Cache

Forcing a complete rebuild, ignoring any existing cached layers, can be useful when troubleshooting a suspected caching issue or when an underlying dependency has changed in a way Docker's cache cannot detect on its own.

docker build --no-cache -t myapp .

Watching Build Output in Detail

More detailed build output, including full command output from each step, can help diagnose exactly what is happening during a build, particularly when troubleshooting a failure.

docker build --progress=plain -t myapp .

Why docker build Matters

docker build is the fundamental command connecting a Dockerfile's declared instructions to an actual, runnable image — understanding its various options is essential for controlling exactly how, and under what conditions, that translation from instructions to artifact actually happens.