ACR retag task

This repo experiments with different ways of re-tagging an ACR image.

Abstract

The purpose of re-tagging images is related to the use of Flux to handle k8s deployments (via AKS in HMCTS) driven by events. In our case, any image published with a given tag pattern on an ACR registry will be automatically (re)deployed .

e.g. <my-app>:latest_<whatever-hash>

Choices

Several approaches regarding the current state of our infrastructure can be made:

1. From the existing pipeline, re-tagging an existing images tagged as :latest, this is the push approach, triggered by Jenkins alongside other steps.

2. Create an ACR task that automatically creates a new tagged image each time a :latest image is published in ACR, this is the event-driven approach

Theses choices can be experimented with the targets provided in the Makefile.

Notice that you may need to create an envfile file to make those scripts run locally.

Experiments

Push approach (Jenkins)

Example

You can create an image representing an application image using the following command:

$ make app-image

Each time you run this command you actually create a new version of your application, bundled as an image tagged as :latest.

From this on, you can experiment the push approach by manually triggering a re-tagging:

$ make re-tag

Discussion

Advantages	Disadvantages
Visible in the pipeline (traceability)	Constrained to Jenkins builds
Ability to opt-in/out

ACR Event approach

Example

ACR allows you to create tasks where you define a given process to happen on a given event.

In our case, the following command creates a re-tagging procedure each time the application image is pushed with the :latest tag:

You can start by creating this task:

$ make task

Verify that you can see your task using the following make commands and other convenient interations:

Available targets:

app-image                       Create new image with random content in ACR
clean                           Clean all
help                            Display help section
list-tasks                      List tasks in the registry
re-tag                          Manually re-tag the app image
repository-clean                Remove non-latest images from the registry
repository-list                 List the available tags in the repository
task                            Create a re-tag task
task-logs                       Logs of the task
task-remove                     Remove the re-tag task
task-trigger                    Manually trigger the task

Now you can create you image using the following command:

$ make app-image

You should the notice that an additional tag will be autimatically created in the registry.

Discussion

Advantages	Disadvantages
Opened to any way the images are updated	Awareness: the tasks are not easily visible if not well documented
Event-based so not preemptive on the way images are built	Tasks lifecycle to be handled correctly

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Other comnmands allow you update/remove the ACR task and to cleanup the registry.