namespace collision on url kernel arg results in downloading iso multiple times

[ubuntu-server-builder]

This bug was originally filed in Launchpad as LP: #1937319

Launchpad details

affected_projects = ['casper (Ubuntu)']
assignee = aciba
assignee_name = Alberto Contreras
date_closed = 2022-08-19T16:37:08.840776+00:00
date_created = 2021-07-22T22:03:17.816933+00:00
date_fix_committed = 2022-08-05T05:08:53.179767+00:00
date_fix_released = 2022-08-19T16:37:08.840776+00:00
id = 1937319
importance = medium
is_complete = True
lp_url = https://bugs.launchpad.net/cloud-init/+bug/1937319
milestone = None
owner = dbungert
owner_name = Dan Bungert
private = False
status = fix_released
submitter = dbungert
submitter_name = Dan Bungert
tags = []
duplicates = [1970595]

Launchpad user Dan Bungert(dbungert) wrote on 2021-07-22T22:03:17.816933+00:00

As listed at https://discourse.ubuntu.com/t/netbooting-the-live-server-installer/14510/135

When attempting a netboot, we can end up in a situation where cloud-init downloads a full iso, only to decide that the first few bytes aren't the expected header and to ignore it.

I suggest an enhancement where a small amount of data is downloaded at first, we check this data for the required #cloud-config, and then use that info to decide to continue to download the file or not.

[ubuntu-server-builder]

Launchpad user James Falcon(falcojr) wrote on 2021-07-23T04:06:57.403417+00:00

How is cloud-init getting pointed to an iso? Is there a way this can happen that isn't the result of a simple misconfiguration?

[ubuntu-server-builder]

Launchpad user Dan Bungert(dbungert) wrote on 2021-07-23T15:28:23.299158+00:00

It's valid for netboot to do something like this:
APPEND root=/dev/ram0 ramdisk_size=1500000 ip=dhcp url=http://releases.ubuntu.com/focal/ubuntu-20.04.1-live-server-amd64.iso
See the top post of that discourse for more details:
https://discourse.ubuntu.com/t/netbooting-the-live-server-installer/14510

So the url argument is rational for netboot, but there is a namespace collision here.

It's my hope that we fix this in multiple ways

1. add a new argument for netboot, one that isn't the generic 'url=', much like how cloud-init can accept 'cloud-config-url' instead of 'url'
2. Address the issue here, so that existing users don't download isos more times than intended until they learn about the fix in Add a spec draft for the new distro namespace. #1

What do you think?

[ubuntu-server-builder]

Launchpad user Dan Bungert(dbungert) wrote on 2021-07-23T15:30:04.129592+00:00

See also: https://discourse.ubuntu.com/t/ubuntu-20-04-installer-downloads-iso-more-than-once/21697/3

[ubuntu-server-builder]

Launchpad user James Falcon(falcojr) wrote on 2021-07-23T17:08:55.449393+00:00

Thanks for the context. Yes, I think your proposal makes sense.

[ubuntu-server-builder]

Launchpad user Michael Hudson-Doyle(mwhudson) wrote on 2021-07-30T03:32:23.018946+00:00

I had a look at the code that does this download and the structure of the APIs used looks to make this kind of sniffing a bit awkward :( Nothing impossible of course but it's not going to be completely trivial either.

[ubuntu-server-builder]

Launchpad user Launchpad Janitor(janitor) wrote on 2022-04-27T15:31:32.557580+00:00

Status changed to 'Confirmed' because the bug affects multiple users.

[ubuntu-server-builder]

Launchpad user Launchpad Janitor(janitor) wrote on 2022-06-03T03:16:01.336234+00:00

This bug was fixed in the package casper - 1.472

---

casper (1.472) kinetic; urgency=medium

• Support iso-url= on the kernel command line as a synonym for url=, to
  help avoid the conflict with cloud-init over that argument. (LP: #1937319)

-- Michael Hudson-Doyle michael.hudson@ubuntu.com Fri, 03 Jun 2022 11:25:33 +1200

[ubuntu-server-builder]

Launchpad user Alberto Contreras(aciba) wrote on 2022-07-20T13:29:13.001119+00:00

PR to avoid downloading urls that does not contain cloud-configs: #1606

[ubuntu-server-builder]

Launchpad user Chad Smith(chad.smith) wrote on 2022-08-05T05:08:46.646400+00:00

Upsream commit landed with a fix for this in cloud-init 8e26b2f

[ubuntu-server-builder]

Launchpad user Brett Holman(holmanb) wrote on 2022-08-19T16:37:10.109619+00:00

This bug is believed to be fixed in cloud-init in version 22.3. If this is still a problem for you, please make a comment and set the state back to New

Thank you.