Samples

Syntax

1. Basic command

FROM

• Create a new image based on the image.
• Format: FROM :
• Example: FROM node:16

RUN

• Specifies the command to be executed during Docker image creation.
• Shell format: RUN
• exec format: RUN ["executable file", "parameter 1", "parameter 2"]
• Example:

RUN apt-get update && apt-get install -y curl

CMD

• Specifies the command to be executed by default when running the container.
• Format:
• Shell format: CMD
• exec format: CMD ["executable file", "parameter 1", "parameter 2"]
• Example:

CMD ["node", "app.js"]

ENTRYPOINT

• Set the execution starting point of the container.
• Similar to CMD, but with more emphasis on fixed execution.
• Format: ENTRYPOINT ["Executable file", "Parameter 1"]
• Example:

ENTRYPOINT ["python3", "script.py"]

COPY

• Copy files or directories to container.
• Format: COPY
• Example:

COPY app.js /usr/src/app/

ADD

• Can copy files + download and unzip URL.
• Format: ADD
• Example:

ADD archive.tar.gz /usr/src/app/

WORKDIR

• Set the working directory where subsequent commands will be executed.
• Format: WORKDIR
• Example:

WORKDIR /usr/src/app

EXPOSE

• Specify the port on which the container will listen.
• Format: EXPOSE
• Example:

EXPOSE 3000

ENV

• Set environment variables.
• Format: ENV
• Example:

ENV NODE_ENV production

ARG

• Specifies parameters to be passed when building Dockerfile.
• Format: ARG =
• Example:

ARG APP_VERSION=1.0

VOLUME

• Set the volume to be shared between the container and the host.
• Format: VOLUME [""]
• Example:

VOLUME ["/data"]

USER

• Set the container execution user account.
• Format: USER [:group]
• Example:

USER 1001

LABEL

• Set metadata.
• Format: LABEL =
• Example:

LABEL maintainer="[email protected]"

2. Advanced Grammar

ONBUILD

• Set the command triggered on the parent image.
• Format: ONBUILD
• Example:

ONBUILD RUN echo "Triggered from base image!"

HEALTHCHECK

• Check container status.
• Format: HEALTHCHECK [option] CMD
• Example:

HEALTHCHECK --interval=30s --timeout=10s \
    CMD curl -f http://localhost/health || exit 1

3. Comment

• Write a comment in the Dockerfile starting with #.
• Example:

# 이 Dockerfile은 Node.js 애플리케이션을 위한 것입니다.

4. Execution order of commands

• Dockerfiles are executed sequentially from top to bottom.
• Caching is applied according to the order of instructions, so for optimization purposes, it is recommended to write instructions that do not change frequently at the top.