Before using the images from somewhere we always look for if other people are also using the same image. And how do we get to know if people are using the image? To answer this, we have enable pull counts for the images. This show total number of times the image is pulled from the registry.centos.org.

How?

For this, we analyse all the nginx access logs. It finds out the number of docker pull happened for a particular image, and  stores the data in disk. Now if the image pull data is already existing, it retrieves the data, adds the value to currently retrieved count and stores it back.

For retrieving and storing pull count according to image tag details it searches through the registry image manifest files, and grep for the tags that matches the sha sum.

While retrieving the data for UI, it goes through the specific volume and retrieve the count using the image tag details. It also verifies the data with the registry to make sure the image details provided is valid ones.