Publishing a Docker image to Bintray

Publishing a Docker image to Bintray isn’t that hard — but you have to know how!

Normally I’m a Java guy. So normally you expect a article about Kotlin, gradle or Maven or something. But the fact that all big CI providers backend on Docker lead to the fact that I have to investigate a little bit time into learning Docker.

Let’s start by showing you how to publish a Docker image to Bintray.

1. Create a Docker Repository

First of all, beside of having a Bintray account of course, you have to create a Docker repository on Bintray. Just go to your overview page, click on “Add new Repository”, choose Docker as type, name it somehow (e.g dockerhub) and click create.

2. Credentials

For a successful docker push you have to set up your credentials in a file located at ~/.dockercfg . According to the docs from Bintray you can receive that file via a simple curl command. Unfortunately it wasn’t working for me. I just got the message:

{ 
   “message” : ”Repository ‘/<BintrayUsername>/<BintrayRepoName>’ does not support Docker API version v1"
}

That’s the reason why I suggest you to create the file manually.
To file needs the following syntax:

I think the file explained everything what do you have to replace 🙃.

3.1 Publishing — The Docker image

Obviously to publishing a Docker image you need a Docker image first. For testing purpose I’ve created a simple Dockerfile like this:

FROM node:8.2.1

To create the image just run the following command. The <ImageName> can be replaced with any name you like (e.g. bintray-publish-test):

docker build -t <ImageName> .

3.2 Publishing — Tagging

Before you can finally publish the image you have to tag it. Bintray needs a special tag name for it. It’s build in the following way:

<Bintray username>-docker-<Bintray RepoName>.bintray.io/<ImageName>

To take the image you have to first find the image via docker images . This will give you a great overview about all the Docker images on your machine. Find the image you have just created and copy the IMAGE ID .

To tag these image run:

docker tag <ImageId> <TagNameFromAbove👆>

Note: This tag is also your “final” image name. If someone wants to use your image in their Dockerfile they have to use these tag as image name.

3.3 Publishing — Publish 🎉

Now you are finally ready to publish your image. And — it is really simple. Just run

docker push <TagNameFromAbove👆>

4.0 Testing

To verify that everything works correctly you can create a new test project.
For that I created a new Dockerfile with the following content:

FROM <DockerTag>
CMD echo “Hello World”

The <DockerTag> is the full name of the tag we have created above 👆.

To make sure that Docker will download the image from Bintray and don’t use a local copy of it remove the images from your machine:

docker rmi <ImageId> -f

Now you can build and run your test Dockerfile :

docker build -t medium-test . 
docker run medium-test

Now you have — hopefully — the Hello World output we expected 🎉.