Create an Image

This second exercise will pick-up the nginx example from the first part. This time, we will replace the default page of the image by creating our own image that contains a different default page.

Go to your test folder (e.g., /Users/yourname/test), in which you have stored the nested html. Create a new file called Dockerfile (in the test folder, not in the html folder). The Dockerfile should have the following content.

FROM nginx
COPY html /usr/share/nginx/html

This Dockerfile is minimalistic and only contains two instructions:

The new image will inherit all properties from the base image nginx (e.g., files, exposed ports, …).
We will alter the base image by copying the local html folder to /usr/share/nginx/html, the place in which nginx will be looking for the default page.

Before you start building, request a listing of all images that are locally available. At this point, the list will likely only contain the nginx image.

$ docker images

To build your own image, execute the following build command from within your test folder, in which the Dockerfile is stored (the dot is important).

$ docker build .
[+] Building 0.2s (7/7) FINISHED
 => [internal] load build definition from Dockerfile
 => => transferring dockerfile: 129B
 => [internal] load .dockerignore
 => => transferring context: 2B
 => [internal] load metadata for docker.io/library/nginx:latest
 => [internal] load build context
 => => transferring context: 189B
 => [1/2] FROM docker.io/library/nginx
 => [2/2] COPY html/ /usr/share/nginx/
 => exporting to image
 => => exporting layers
 => => writing image sha256:3a4c...

The last line tells you that an image with the id 3a4c... has been stored. The command docker images will now list this image and include a <none> for repository and tag. The image is fully functional and can be used via its image id.

$ docker run --rm -p 8080:80 3a4c

However, refering to images via their id is very tedious and hard to remember. Instead, it is preferrable to tag the image. This can either achieved by running docker tag 3a4c myimg:1.2.3, or by directly including one or more tags directly in the build command:

$ docker build -t myimg:1.2.3 .
...
=> => writing image sha256:3a4c...
=> => naming to docker.io/library/myimg:1.2.3

Regardless of which form you chose, a docker images will now list your image under the provided name and version. You can now run the image by name.

docker run --rm -p8080:80 myimg:1.2.3

Please note that this image is only locally available on your machine. To make it available to others, you have to push it to a registry, like Dockerhub. We will cover this in one of the upcoming lectures.