Easier use of an internal helper image mirror

[kasimon]

This is somehow related to #46 but with a slightly different focus. Our servers cannot access the internet directly. They rely on an internal mirror for packages and other downloadable assets. The main problems we are having with the handling of the helper image are the following:

• The HELPER_URL variable defines both the location of the images (https://cdn.synnefo.org/) and the exact versioned file name (snf_image_helper_image-0.20.tar.xz).
• The only way to point snf-image-update-helper to an alternative location where it can access the helper images is by settings HELPER_URL in /etc/default/snf-image-update-helper.
• This means updates of the snf-image package and changing the defaults file have to be synchronized, which can be a hassle especially when the file content is controlled by a configuration management tool like puppet.

Suggestions to make snf-image more mirror-friendly:

• replace/supplement HELPER_URL by a second HELPER_URL_BASE variable containing the common location of all helper images, e.g. https://cdn.synnefo.org/ or https://mirror.somecompany.com/snf-images/
• if HELPER_URL is not set and HELPER_URL_BASE is, let snf-image-update-helper build the full path to the image itself, as it should know the version it needs. This would allow to statically set the HELPER_URL_BASE via config management without the need to change it when the package is updated.
• Provide a mirror mechanism to clone all existing helper images to a local mirror, for example via ftp or rsync. Run before each update of the internal package mirror, this would allow seamless updates without further manual intervention.

[skalkoto]

Well the HELPER_URL_BASE thing you mention is already implemented, but it is done the Debian way using debconf. If you do debconf-show snf-image on a system that has snf-image installed:

# debconf-show snf-image
* snf-image/dlurl:
* snf-image/update-helper: true

You will see that dlurl is set to andupdate-helperis set totrue. The first variable is theHELPER_URL_BASEyou mention. The second variable controls whether the helper image should be automatically downloaded during the post-install phase. If thedlurlis empty, then snf-image will use the default base url. The*in front of them means that the user has already been asked about this (the first time he has installed snf-image) and we shouldn't ask him again the next time snf-image get's updated. Based on the value ofdlurl, debconf will set theHELPER_URLfield of/etc/default/snf-image-update-helperevery time snf-image gets updated, as long as the first line of the file is###DEBCONF###:

###DEBCONF###
# the configuration of this file will be done by debconf as long as the
# first line of the file says '###DEBCONF###'
#
# you should use dpkg-reconfigure snf-image to configure this file
#
# HELPER_URL: URL to use to download the snf-image-helper image
HELPER_URL=http://cdn.synnefo.org/snf_image_helper_image-0.20.tar.xz

if you do dpkg-reconfigure snf-image you will be asked about what base url to use in order to create the HELPER_URL. If you pick https://mirror.somecompany.com/snf-images/, every time you update snf-image the HELPER_URL will look like this: https://mirror.somecompany.com/snf-images/snf_image_helper_image-<VERSION>.tar.xz

[kasimon]

Awesome, that's even more convenient. Thank you for the detailed explanation.

[kasimon]

Works great. But being able to easily mirror the snf helper images would be great.

[skalkoto]

Yes, I know. We'll do something about this too.