Docker image

• Create a Dockerfile

  # Always start with baseimage -> ubuntu
  FROM  ubuntu

  RUN  apt update -y
  RUN apt install nginx -y

  VOLUME [ "/var/www/html" ] # Information only

  LABEL version="1" description="This is alpha image"

  RUN  apt install curl -y

  EXPOSE 80 # Information only

  HEALTHCHECK --interval=30s --timeout=30s --start-period=5s --retries=3 CMD ["sh", "-c", "curl -f localhost || exit 1" ]

  CMD  [ "nginx", "-g", "daemon off;"]

Points to remember

• Always start with base image (ubuntu : example)

• Volume : it's just for information, it's actually does not expose volume

• expose : it's just for information, it's actually does not expose port

• To expose port and volume must specific in cli

DockerFile reference : https://docs.docker.com/engine/reference/builder/#workdir

CMD VS ENTRYPOINT : https://docs.docker.com/engine/reference/builder/#understand-how-cmd-and-entrypoint-interact

Command to build image

docker build -t username/image_name .

#to push to repo
docker pull username/image

CLI

docker run -p 80:80 -v /home/ak/nginx:/var/www/html -d --name nginx nginx

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ENV

In a Dockerfile, you can set environment variables using either $key or ${key} syntax. The ${key} syntax offers additional benefits with Bash modifiers like ${variable:-word} or ${variable:+word}

For example:

• ${variable:-word}: Expands to the value of variable if it's set; otherwise, expands to word.

• ${variable:+word}: Expands to word if variable is set; otherwise, expands to an empty string

When using these patterns in CMD or ENTRYPOINT, remember that variable substitution is handled by the command shell, not the Docker builder. Here's a concise example

ENV name=somevalue
ENTRYPOINT ["sh", "-c", "echo hello world"]

In this setup, the ${name} in sh -c is interpreted by the shell during runtime, not during Docker image building. This flexibility allows you to leverage Bash features in your Docker environment