Creating a docker image makes use of docker file. It contains specific command or syntax to tell docker what we want.

Commands

1. FROM:

   Base image for new image

   

2. WORKDIR

   Instruction is used to set the working directory for any RUN, CMD, ENTRYPOINT, COPY, and ADD instructions that follow it in the Dockerfile. It doesn't create a new directory but rather sets the working directory for subsequent instructions.

   

3. COPY

   instruction is used to copy files or directories from the build context (the directory containing the Dockerfile) into the filesystem of the container.

   

4. RUN

   Instruction is used to execute commands during the image build process.

   It allows you to install packages, update configurations, or perform any other tasks necessary for setting up your application or environment within the Docker image.

   

5. EXPOSE

   Instruction informs Docker that the container listens on specified network ports at runtime. It does not actually publish the specified ports; it serves as documentation for the user about the ports to which the service inside the container will respond.

   

6. ENV

   instruction is used to set environment variables. Environment variables can be used to customize the behavior of software running in a Docker container.

   

7. ARG

   Instruction is used to define build-time variables. These variables are set during the build and can be used as variables in the Dockerfile. They provide a way to pass information into the Docker build process.

   

8. VOLUME

   instruction in a Dockerfile is used to create a mount point and associate it with a directory in the container that can be used for persisting data. It is often used to handle data that should persist outside the lifecycle of the container, such as database files, configuration files, or user uploads.

   

9. CMD

   instruction provides the default command or parameters to execute when the container starts. It is not executed during the image build but specifies the primary command that should run when the container is launched.

   

   

   

10. ENTRYPOINT

    instruction in a Dockerfile is used to set the primary command that will be executed when a container is run. It allows you to configure a container to run a specific command as the default command, and it can also be used to pass default arguments to the command.

    

ENTRYPOINT VS CMD

Both are instruction for defining the default command to run when a container starts

When both CMD and ENTRYPOINT instructions are used in a Dockerfile, the CMD instruction provides default arguments for the ENTRYPOINT instruction. This means that if a user runs a container without specifying a command, the command defined in CMD will be used as arguments to the command defined in ENTRYPOINT.

The basic syntax looks like this:

ENTRYPOINT ["executable", "param1", "param2"]
CMD ["param3", "param4"]

Here's an example to illustrate this:

FROM ubuntu:20.04

# Set the entry point to echo
ENTRYPOINT ["echo", "Hello"]

# Set default command arguments
CMD ["world"]

In this example:

• The ENTRYPOINT is set to the echo command with the initial parameters "Hello".

• The CMD sets default command arguments to "world".

When you run a container without specifying a command, the default command from CMD is used as arguments to the command specified in ENTRYPOINT:

docker run myimage

This will effectively run:

echo Hello world

If you run the container with a specific command, it overrides both CMD and ENTRYPOINT:

docker run myimage "Goodbye"

This will run:

echo Goodbye

In summary, when both CMD and ENTRYPOINT are used, CMD provides default arguments to the command specified in ENTRYPOINT. Users can still override both the CMD and ENTRYPOINT by providing a command when running the container.

EXAMPLE

REFERENCE

EXTRA COMMANDS: