moby--moby/docs/sources/docker-hub/official_repos.md

page_title: Guidelines for Official Repositories on Docker Hub page_description: Guidelines for Official Repositories on Docker Hub page_keywords: Docker, docker, registry, accounts, plans, Dockerfile, Docker Hub, docs, official, image, documentation

Introduction

You’ve been given the job of creating an image for an Official Repository hosted on Docker Hub Registry. These are Docker, Inc.’s guidelines for getting that task done. Even if you’re not planning to create an Official Repo, you can think of these guidelines as best practices for image creation generally.

This document consists of three major sections:

• Expected files, resources and supporting items for your image
• Examples embodying those practices
• Instructions for submitting your work

Expected Files & Resources

A Git repository

Your image needs to live in a Git repository, preferably on GitHub. (If you’d like to use a different provider, please [contact us](TODO: link) directly.) Docker strongly recommends that this repo be publicly accessible.

If the repo is private or has otherwise limited access, you must provide a means of at least “read-only” access for both general users and for the docker-library maintainers, who need access for review and building purposes.

A Dockerfile

Complete information on Dockerfiles can be found in the Reference section. We also have a page discussing best practices for writing Dockerfiles (TODO: link). Your Dockerfile should adhere to the following:

• It must be written either by using FROM scratch or be based on another, established Official Image.
• It must follow Dockerfile best practices. These are discussed in the [Best Practices document](TODO: link). In addition, Docker, Inc. engineer Michael Crosby has a good discussion of Dockerfiles in this blog post.

While ONBUILD triggers are not required, if you choose to use them you should:

• Build both ONBUILD and non-ONBUILD images, with the ONBUILD image built FROM the non-ONBUILD image.
• The ONBUILD image should be specifically tagged, for example, ruby:latest and ruby:onbuild, or ruby:2 and ruby:2-onbuild.

A short description

Include a brief description of your image (in plaintext). Only one description is required; you don’t need additional descriptions for each tag. The file should also:

• Be named README-short.txt
• Reside in the repo for the “latest” tag
• Not exceed 200 characters.

A logo

Include a logo of your company or the product (png format preferred). Only one logo is required; you don’t need additional logo files for each tag. The logo file should have the following characteristics:

• Be named logo.png
• Should reside in the repo for the “latest” tag
• Should be 200px min. in one dimension, 200px max. in the other.
• Square or wide (landscape) is preferred over tall (portrait), but exceptions can be made based on the logo needed.

A long description

Include a comprehensive description of your image (in markdown format). Only one description is required; you don’t need additional descriptions for each tag. The file should also:

• Be named README.md
• Reside in the repo for the “latest” tag
• Be no longer than absolutely necessary, while still addressing all the content requirements.

In terms of content, the long description must include the following sections:

• Overview & Links
• How-to/Usage
• User Feedback
• License

Overview & links

A section providing (a) an overview of the software contained in the image, similar to the introduction in a Wikipedia entry and (b) a selection of links to outside resources that help to describe the software.

How-to/usage

A section that describes how to run and use the image, including common use cases and example Dockerfiles (if applicable). Try to provide clear, step-by-step instructions wherever possible.

User Feedback

This section should have two parts, one explaining how users can contribute to the repo and one explaining how to report issues with the repo.

Contributing

In this part, point users to any resources that can help them contribute to the project. Include contribution guidelines and any specific instructions related to your development practices. Include a link to Docker’s resources for contributors. Be sure to include contact info, handles, etc. for official maintainers.

Issues

Include a brief section letting users know where they can go for help and how they can file issues with the repo. Point them to any specific IRC channels, issue trackers, contacts, additional “how-to” information or other resources.

License

Include a copy of any applicable license. Docker recommends using the license of the software contained in the image, provided it allows Docker, Inc. to legally build and distribute the image. Otherwise Docker recommends adopting the Apache license.

Example

Below are sample short and long description files for an imaginary image containing Ruby on Rails.

Short description

README-short.txt

Ruby on Rails is an open-source application framework written in Ruby. It emphasizes best practices such as convention over configuration, active record pattern, and the model- view-controller pattern.

Long description

README.md

What is Ruby on Rails

Ruby on Rails, often simply referred to as Rails, is an open source web application framework which runs via the Ruby programming language. It is a full-stack framework: it allows creating pages and applications that gather information from the web server, talk to or query the database, and render templates out of the box. As a result, Rails features a routing system that is independent of the web server.

wikipedia.org/wiki/Ruby_on_Rails

How to use this image

1. create a Dockerfile in your rails app project

FROM rails:onbuild

Put this file in the root of your app, next to the Gemfile.

This image includes multiple ONBUILD triggers so that should be all that you need for most applications. The build will ADD . /usr/src/app, RUN bundle install, EXPOSE 3000, and set the default command to rails server.

2. build the rails app image

   docker build -t my-rails-app .

3. start the rails app container

   docker run --name some-rails-app -d my-rails-app

Then go to http://container-ip:3000 in a browser. On the other hand, if you need access outside the host on port 8080:

docker run --name some-rails-app -p 8080:3000 -d my-rails-app

Then go to http://localhost:8080 or http://host-ip:8080 in a browser.