What Is a Dockerfile?

A Dockerfile is a text document containing a set of instructions to assemble a Docker image. Each instruction performs a specific action, such as installing packages, copying files, or defining startup commands. Proper use of Dockerfile instructions is crucial for building efficient containers.

Key Dockerfile Instructions

• FROM: Sets the base image for your new image.
• RUN: Executes a command in a new layer on top of the current image and commits the result.
• CMD: Specifies the default command to run when a container is started.
• COPY: Copies files and directories from the build context into the container filesystem.
• ADD: Similar to COPY but with additional features like extracting archives.
• ENV: Sets environment variables.
• EXPOSE: Informs Docker which ports the container listens on at runtime.
• ENTRYPOINT: Configures a container to run as an executable.
• VOLUME: Creates a mount point for external storage volumes.
• WORKDIR: Sets the working directory for subsequent instructions.