{"id":23589,"date":"2022-10-03T14:09:46","date_gmt":"2022-10-03T14:09:46","guid":{"rendered":"https:\/\/www.devopsschool.com\/blog\/?p=23589"},"modified":"2025-07-12T05:40:18","modified_gmt":"2025-07-12T05:40:18","slug":"creating-docker-image-step-by-step-guide","status":"publish","type":"post","link":"https:\/\/www.devopsschool.com\/blog\/creating-docker-image-step-by-step-guide\/","title":{"rendered":"Docker Tutorials: Image – Creating Docker Image Step by Step"},"content":{"rendered":"\n

Setting up the prerequisites<\/h3>\n\n\n\n

Listing images on the host<\/p>\n\n\n

$ docker images<\/code><\/span><\/pre>\n\n\n
If you do not have ubuntu:14.04 images, please download it using following commands.<\/p>\n\n\n
$ docker pull ubuntu:14.0 <\/code><\/span><\/pre>\n\n\n
Verify the ubuntu:14.0 image by running the following commands.<\/p>\n\n\n
$ docker run -t -i -d ubuntu:14.04 \/bin\/bash<\/code><\/span><\/pre>\n\n\n
Method 1: You can update a container created from an image and commit the results to an image.<\/h3>\n\n\n\n
We will use training\/sinatra image pretty useful for creating the images for Method1.<\/p>\n\n\n\n
To update an image you first need to create a container from the image you\u2019d like to update.<\/p>\n\n\n
$ docker run -t -i training\/sinatra \/bin\/bash<\/code><\/span><\/pre>\n\n\n
Inside our running container first let\u2019s update apt, httpd and install git.<\/p>\n\n\n
$ root@0<\/span>b2616b0e5a8:\/# apt-get update<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n
$ root@0<\/span>b2616b0e5a8:\/# apt-get install -y git<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n
$ root@0<\/span>b2616b0e5a8:\/# apt-get install -y httpd<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Once this has completed let\u2019s exit our container using the exit command. Now you have a container with the change you want to make. You can then commit a copy of this container to an image using the docker commit command.<\/p>\n\n\n
$ docker commit -m \"Added json gem\"<\/span> -a \"Rajesh Kumar\"<\/span> 0<\/span>b2616b0e5a8 scmgalaxy\/sinatra:v2<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
Here you\u2019ve used the docker commit command. You\u2019ve specified two flags: -m and -a. The -m flag<\/strong> allows us to specify a commit message, much like you would with a commit on a version control system. The -a flag<\/strong> allows us to specify an author for our update.<\/p>\n\n\n\n
You\u2019ve also specified the container you want to create this new image from, 0b2616b0e5a8<\/strong> (the ID you recorded earlier) and you\u2019ve specified a target for the image:scmgalaxy\/sinatra:v2<\/code><\/p>\n\n\n\n
It consists of a new user, scmgalaxy<\/strong>, that you\u2019re writing this image to. You\u2019ve also specified the name of the image sinatra<\/strong>. Finally you\u2019re specifying a tag for the image: v2<\/strong>.<\/p>\n\n\n\n
You can then look at our new scmgalaxy\/sinatra image using the docker images command.<\/p>\n\n\n
$ docker images<\/code><\/span><\/pre>\n\n\n
To use our new image to create a container you can then:<\/strong><\/p>\n\n\n
$ docker run -t -i ouruser\/sinatra:v2 \/bin\/bash<\/code><\/span><\/pre>\n\n\n
Method 2: You can use a Dockerfile to specify instructions to create an image.<\/h3>\n\n\n\n
Using the docker commit command is a pretty simple way of extending an image but it\u2019s a bit cumbersome and it\u2019s not easy to share a development process for images amongst a team. Instead you can use a new command, docker build, to build new images from scratch.<\/p>\n\n\n\n
To do this you create a Dockerfile<\/strong> that contains a set of instructions that tell Docker how to build our image.<\/p>\n\n\n\n
First, create a directory and a Dockerfile.<\/p>\n\n\n
\n$ mkdir sinatra\n$ cd sinatra\n$ touch Dockerfile\n<\/code><\/span><\/pre>\n\n\n
Each instruction creates a new layer of the image<\/strong>. Try a simple example now for building your own Sinatra image for your fictitious development team.<\/p>\n\n\n
\nFROM ubuntu:14.04<\/span>\nMAINTAINER Rajesh Kumar \"rajesh@scmgalaxy.com\"<\/span>\nRUN apt-get<\/span> update && apt-get<\/span> install -y git httpd\n<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
Examine what your Dockerfile does. Each instruction prefixes a statement and is capitalized.<\/p>\n\n\n
INSTRUCTION statement<\/code><\/span><\/pre>\n\n\n
The first instruction FROM<\/strong> tells Docker what the source of our image is, in this case you\u2019re basing our new image on an Ubuntu 14.04<\/strong> image. The instruction uses the MAINTAINER<\/strong> instruction to specify who maintains the new image.<\/p>\n\n\n\n
Lastly, you\u2019ve specified two RUN<\/strong> git and httpd<\/p>\n\n\n\n
Now let\u2019s take our Dockerfile<\/strong> and use the docker build<\/strong> command to build an image.<\/p>\n\n\n
$ docker build -t scmgalaxy\/sinatra:v3 .\/ <\/code><\/span><\/pre>\n\n\n
You\u2019ve specified our docker build command and used the -t<\/strong> flag to identify our new image as belonging to the user scmgalaxy<\/strong>, the repository name sinatra<\/strong> and given it the tag v2<\/strong>.<\/p>\n\n\n
$ docker run -t -i scmgalaxy\/sinatra:v2 \/bin\/bash\/ <\/code><\/span><\/pre>\n\n\n
Setting tags on an image<\/strong><\/p>\n\n\n
$ docker tag 5db5f8471261 scmgalaxy\/sinatra:dev<\/code><\/span><\/pre>\n\n\n
The docker tag command takes the ID of the image, here 5db5f8471261<\/strong>, and our user name, the repository name and the new tag.<\/p>\n\n\n
$ docker images scmgalaxy\/sinatra<\/code><\/span><\/pre>\n\n\n
Remove an image from the host<\/p>\n\n\n
$ docker rmi training\/sinatra<\/code><\/span><\/pre>\n\n