download images to k8s-workers before initiating charm upgrade

Bug #1991369 reported by Tom Haddon
6
This bug affects 1 person
Affects Status Importance Assigned to Milestone
Canonical Juju
Triaged
Wishlist
Unassigned

Bug Description

This isn't so much a bug as a feature request/query. It applies to k8s charms only.

Would it be possible to have Juju download the images to be used by a charm before initiating a charm upgrade? In the case where you have a number of images, and any of them are large, there can be quite a long delay between an initial unit of an application being terminated by Kubernetes to initiate a charm upgrade and the time when the workload is ready to receive traffic (up to 10 minutes in one particular case on a production service we're currently running). If other units are on the same k8s-worker, the charm upgrade process is _much_ quicker, because the images are already on the relevant worker.

It would be very nice if we could avoid these longer charm upgrades (during which time `n - 1` units are available to serve traffic, where `n` is the number of units the application is scaled to).

Tags: canonical-is
Tom Haddon (mthaddon)
tags: added: canonical-is
Revision history for this message
John A Meinel (jameinel) wrote :

I think this is an interesting idea, but we'd want to make sure we do so in a reasonable manner. Is there a way we could tell K8s "don't bring down the Nth unit until the N+1 unit is available"?

Revision history for this message
Harry Pidcock (hpidcock) wrote :

This isn't really possible due to not knowing where the pod will be scheduled. I think what we can do here is add support for configuration of rolling upgrades.

Changed in juju:
importance: Undecided → Wishlist
milestone: none → 3.1-beta1
status: New → Triaged
Changed in juju:
milestone: 3.1-beta1 → 3.2-beta1
Changed in juju:
milestone: 3.2-beta1 → 3.2-rc1
Changed in juju:
milestone: 3.2-rc1 → 3.2.0
Changed in juju:
milestone: 3.2.0 → 3.2.1
Changed in juju:
milestone: 3.2.1 → 3.2.2
Changed in juju:
milestone: 3.2.2 → 3.2.3
Changed in juju:
milestone: 3.2.3 → 3.2.4
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