nagswarnaa / Docker

Docker Commands

Writing a Dockerfile involves understanding a set of commands and directives that define the environment and the steps needed to create and run a Docker image. Here’s a list of commonly used Dockerfile commands with brief explanations:

Common Dockerfile Commands

1. FROM:

   • Syntax: FROM <image>[:<tag>]
   • Purpose: Specifies the base image to use for the Docker image.
   • Example: FROM openjdk:11-jdk-slim

2. WORKDIR:

   • Syntax: WORKDIR <path>
   • Purpose: Sets the working directory inside the container.
   • Example: WORKDIR /usr/src/app

3. COPY:

   • Syntax: COPY <src> <dest>
   • Purpose: Copies files or directories from the host file system into the container.
   • Example: COPY . .

4. RUN:

   • Syntax: RUN <command>
   • Purpose: Executes a command in the shell during the image build process.
   • Example: RUN javac InteractiveProgram.java

5. CMD:

   • Syntax: CMD ["executable", "param1", "param2"]
   • Purpose: Specifies the command to run within the container when it starts.
   • Example: CMD ["java", "InteractiveProgram"]

6. ENV:

   • Syntax: ENV <key>=<value>
   • Purpose: Sets an environment variable.
   • Example: ENV JAVA_HOME /usr/lib/jvm/java-11-openjdk

7. EXPOSE:

   • Syntax: EXPOSE <port>
   • Purpose: Informs Docker that the container listens on the specified network ports at runtime.
   • Example: EXPOSE 8080

8. ARG:

   • Syntax: ARG <name>[=<default value>]
   • Purpose: Defines a build-time variable.
   • Example: ARG VERSION=1.0

9. ENTRYPOINT:

   • Syntax: ENTRYPOINT ["executable", "param1", "param2"]
   • Purpose: Configures a container to run as an executable.
   • Example: ENTRYPOINT ["java", "-jar", "/usr/src/app/myapp.jar"]

10. VOLUME:

    • Syntax: VOLUME ["/data"]
    • Purpose: Creates a mount point with the specified path and marks it as holding externally mounted volumes from the host or other containers.
    • Example: VOLUME ["/var/log/myapp"]

11. USER:

    • Syntax: USER <username or UID>
    • Purpose: Sets the user name or UID to use when running the image and for any RUN, CMD, and ENTRYPOINT instructions that follow it in the Dockerfile.
    • Example: USER appuser

12. LABEL:

    • Syntax: LABEL <key>=<value>
    • Purpose: Adds metadata to an image.
    • Example: LABEL version="1.0"

13. ONBUILD:

    • Syntax: ONBUILD <command>
    • Purpose: Adds a trigger instruction to the image that will be executed when the image is used as a base for another build.
    • Example: ONBUILD RUN apt-get update

Example Dockerfile

Here's a complete example Dockerfile for the Java program from earlier:

# Use an official OpenJDK JDK runtime as a parent image
FROM openjdk:11-jdk-slim

# Set the working directory inside the container
WORKDIR /usr/src/app

# Copy the current directory contents into the container at /usr/src/app
COPY . .

# Compile the Java program
RUN javac InteractiveProgram.java

# Run the program
CMD ["java", "InteractiveProgram"]

Docker Commands for Managing Dockerfiles

1. Building an Image:

   • Command: docker build -t <image_name> .
   • Example: docker build -t java-interactive-program .

2. Running a Container:

   • Command: docker run <options> <image_name>
   • Example: docker run -it java-interactive-program

3. Listing Images:

   • Command: docker images

4. Removing an Image:

   • Command: docker rmi <image_name>
   • Example: docker rmi java-interactive-program

5. Viewing Container Logs:

   • Command: docker logs <container_id>

These commands and instructions should help you write and manage Dockerfiles effectively.