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DockerImage.md

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How to Create a Docker Image

Interactive Method

The following is a set of simplified steps to creating an image interactively:

  • Install Docker and launch the Docker engine
  • Open a terminal session
  • Use the following Docker run command to start an interactive shell session with a container launched from the image specified by image_name:tag_name:
$ docker run -it image_name:tag_name bash
  • You can also identify your container with something more meaningful by assigning your own name using the – name operator in the Docker run command.

Example:

A container environment based on the latest version of Ubuntu:

$ docker run --name ubuntu  -it ubuntu bash

Now configure your container environment by, for example, installing all the frameworks, dependencies, libraries, updates, and application code you need. The following simple example adds an NGINX server:

# apt-get update && apt-get install -y nginx

List active container processes

$ docker ps

Save your image using the Docker commit command, specifying either the ID or name of the container from you which want to create it:

 $ docker commit keen_gauss ubuntu_testbed

We supplied the name of our container and called the resulting image ubuntu_testbed.

Docker images command to see the image you’ve just created:

$ docker images

Dockerfile Method

The Dockerfile method is a three-step process whereby you create the Dockerfile and add the commands you need to assemble the image.

Command Purpose
FROM To specify the parent image.
WORKDIR To set the working directory for any commands that follow in the Dockerfile.
RUN To install any applications and packages required for your container.
COPY To copy over files or directories from a specific location.
ADD As COPY, but also able to handle remote URLs and unpack compressed files.
ENTRYPOINT Command that will always be executed when the container starts. If not specified, the default is /bin/sh -c
CMD Arguments passed to the entrypoint. If ENTRYPOINT is not set (defaults to /bin/sh -c), the CMD will be the commands the container executes.
EXPOSE To define which port through which to access your container application.
LABEL To add metadata to the image.

Example

# Use the official Ubuntu 18.04 as base
FROM ubuntu:18.04
# Install nginx and curl
RUN apt-get update &&
apt-get upgrade -y &&
apt-get install -y nginx curl &&
rm -rf /var/lib/apt/lists/*

Use the Docker build command to create your Docker image. Use the -t flag to set an image name and tag:

$ docker build -t my-nginx:0.1