.zsync files for the weekly live images

[Roland Clobus]

Hello Debian-Images team,

I've tested the .zsync files on [1].
They currently don't work, because the original filename
(live-image-amd64.hybrid.iso) is embedded in those files.

As a fix, I see several possibilities, which do you prefer?

1) Turn off zsync
2) Keep zsync, and generate unique filenames

Option 1 would possibly increase the amount of traffic on
get.debian.org. Are metrics available whether the .zsync files are used
at all?
I haven't tested whether the zsync method will work properly for the
live images, as they contain a huge squashfs file embedded in the iso
file (so a compressed file inside another compressed file), so I don't
know whether it will help in saving bandwidth.

Option 2 would mean that (with the current code) filenames can be
generated with the structure
`{something-we-decide}-{architecture}.hybrid.iso`, e.g.
`debian-live-testing-gnome-amd64.hybrid.iso`. This is different from the
current names on [1].
If we go for option 2, it will need (small) changes in the `live-build`,
`live-setup` and `jenkins.debian.net` git repos.

With kind regards,
Roland Clobus

[1] https://get.debian.org/images/weekly-live-builds/amd64/iso-hybrid/

[Roland Clobus]

Post by Roland Clobus
Hello Debian-Images team,
I've tested the .zsync files on [1].
They currently don't work, because the original filename
(live-image-amd64.hybrid.iso) is embedded in those files.
As a fix, I see several possibilities, which do you prefer?
1) Turn off zsync
2) Keep zsync, and generate unique filenames
Option 1 would possibly increase the amount of traffic on
get.debian.org. Are metrics available whether the .zsync files are used
at all?
I haven't tested whether the zsync method will work properly for the
live images, as they contain a huge squashfs file embedded in the iso
file (so a compressed file inside another compressed file), so I don't
know whether it will help in saving bandwidth.
Option 2 would mean that (with the current code) filenames can be
generated with the structure
`{something-we-decide}-{architecture}.hybrid.iso`, e.g.
`debian-live-testing-gnome-amd64.hybrid.iso`. This is different from the
current names on [1].
If we go for option 2, it will need (small) changes in the `live-build`,
`live-setup` and `jenkins.debian.net` git repos.
With kind regards,
Roland Clobus
[1] https://get.debian.org/images/weekly-live-builds/amd64/iso-hybrid/

In my previous mail I've expressed my doubts that zsync would be able do
reduce the amount of bytes that is to be downloaded. I was able to do an
experiment now, and it looks good.

With the GNOME images from 2023-04-03 and 2023-04-10 I got the following
output:
```
verifying download...checksum matches OK
used 3612643328 local, fetched 84375881
```

In order to do so, I had to convince zsync to use different filename
(which I managed by splitting the zsync file into its text and binary
part, adjusting the text part and combining both parts again).

Of the 3.6GB only 84MB needed to be downloaded, which is quite
impressive, given that the compressed file `filesystem.squashfs` also
has many differences.

This looks promising enough to prepare for option 2.

With kind regards,
Roland Clobus

PS: I'm not the only one reporting the issue with zsync:
https://lists.debian.org/debian-cd/2023/04/msg00016.html

[Roland Clobus]

Hello Debian-Images team,

(and reply to self for the second time) :-)

Post by Roland Clobus
I've tested the .zsync files on [1].
They currently don't work, because the original filename
(live-image-amd64.hybrid.iso) is embedded in those files.

I've chosen to turn off zsync:
https://salsa.debian.org/images-team/live-setup/-/merge_requests/3

Reasons:
* The package zsync was orphaned for 1.5 years ago
* The package zsync does not support https for the URL with the .zsync file
* Minor reason: The live-build-binary script could generate the images
with the correct filename part, but the extension (.hybrid.iso) is fixed
by the live-build package.

With kind regards,
Roland Clobus

[1] https://get.debian.org/images/weekly-live-builds/amd64/iso-hybrid/

[Steve McIntyre]

Post by Roland Clobus
Hello Debian-Images team,
(and reply to self for the second time) :-)

Post by Roland Clobus
I've tested the .zsync files on [1].
They currently don't work, because the original filename
(live-image-amd64.hybrid.iso) is embedded in those files.

https://salsa.debian.org/images-team/live-setup/-/merge_requests/3

Nod, fair enough. Merged.

Post by Roland Clobus
* The package zsync was orphaned for 1.5 years ago
* The package zsync does not support https for the URL with the .zsync file
* Minor reason: The live-build-binary script could generate the images with
the correct filename part, but the extension (.hybrid.iso) is fixed by the
live-build package.

ACK.