Watching Container Images for Updates

by | May 9, 2017

The majority of Docker users do not built their images from scratch, instead they are built on top of base images that have been created and published by others. Usually these are official images that have been created by an organization or community and submitted to Docker Inc. and the community for official review.

Images should be regularly updated by their publishers to include the latest content like the latest release of operating system packages to add new features or fixes to security vulnerabilities or new versions of an application or software library. As a developer how do I know when an image has been pushed?

DockerHub supports the concept of webhooks that allow a user to receive a notification via an HTTP message when a new image has been pushed. This feature can be used in a number of ways, most commonly it’s used to trigger builds or deployments of applications based on a specific image. This feature has a major limitation: It only supports webhooks for images owned by a user, meaning you can trigger webhooks for images you have created but not for other images such as a base image from an official publisher.

Yesterday the Debian team updated their base image; you can inspect the image here using the Anchore Navigator. But how would you know that the image has been updated? The most common approach is just to try and pull the image to see if a new version has been published.

# docker pull debian:latest

If an updated image is present the docker client will download the newer image.

Trying to pull repository docker.io/library/debian ...
sha256:476959f29a17423a24a17716e058352ff6fbf13d8389e4a561c8ccc758245937: Pulling from docker.io/library/debian
10a267c67f42: Pull complete
Digest: sha256:476959f29a17423a24a17716e058352ff6fbf13d8389e4a561c8ccc758245937
Status: Downloaded newer image for docker.io/debian:latest

If you already have the latest image then the docker client will report that your image is up to date.

Trying to pull repository docker.io/library/debian ...
sha256:476959f29a17423a24a17716e058352ff6fbf13d8389e4a561c8ccc758245937: Pulling from docker.io/library/debian
Digest: sha256:476959f29a17423a24a17716e058352ff6fbf13d8389e4a561c8ccc758245937
Status: Image is up to date for docker.io/debian:latest

One of the most popular free features of the Anchore Navigator is the ability to subscribe to images in order to receive notifications when images are updated.

If you don’t already have a free account on the Navigator then head over to https://anchore.io and sign up. Once you’ve signed up you can search for the image that you wish to monitor.

In the search results you will see a list of repositories. Anchore Navigator can search through all public images on DockerHub. You will see two types of repositories: Analyzed and Preview.

Repositories and TAGs that Anchore is monitoring. For these repositories and TAGS any time a new image is pushed Anchore will download the image and perform detailed inspection including image metadata, package manifests, file lists, security vulnerabilities and policies.

Repositories that are publicly available on DockerHub but that Anchore has not yet downloaded images.

For example searching for debian gives the following initial results.

As you can see the first two repositories in the results list have already been analyzed and you can select the repository to view a list of tags and inspect individual images.

If the repository and tag that you wish to monitor has not yet been analyzed you can press the button to submit this TAG to Anchore to be analyzed.

All the official repositories and several hundred of the most popular public repositories are already analyzed by Anchore so the chances are you’ll find the image you are looking for right away.

Here you can see the overview page for the official Debian image. If you want to receive notifications from Anchore when the image is updated press the Subscribe button and Anchore will notify you when the image has been updated.

You can unsubscribe from the image from the image’s overview page and you can see a list of your image subscriptions and favorited images from the “My Images” page accessible from the left navigation menu.

Here’s an example notification email including details of which subscribed images have been updated. From here you can click on the links to be taken to the overview for the new images:

This is just one example of the features available for free to all Anchore Navigator users.
You can read more about the Anchore Navigator here or better yet sign up for free to start analyzing images today.

Subscribe to an Image on Anchore.io

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