[Bug 1970595] [NEW] The server installer double or triple fetches source ISO file

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Hello,

I'm not sure if this is bug or expected behavior but here we go.

I was doing server reinstall from already installed linux OS via grub
bootstraping (to continue installation via SSH due to lacking access to
the server's physical console). I noticed that ISO file pointed by url
bootoption is fetched three times by Ubuntu installer. I did some
checking and this is my observation.

ISO file: ubuntu-22.04-live-server-amd64.iso 
(SHA256: 84aeaf7823c8c61baa0ae862d0a06b03409394800000b3235854a6b38eb4856f)

IP used:
100.64.241.175 / local-install.vm - http server providing ISO and  {meta,user}-data files
100.64.100.100  - static IP for reinstalled server
100.64.0.1 - default gw
100.64.255.255 - DNS resolver

I tested two cases. One with DNS support and second one without DNS
resolver in place.

My grub.cfg looks like that:

menuentry 'Install with DNS support' {
  load_video
  gfxmode text
  insmod gzio
  insmod part_msdos
  insmod part_gpt
  insmod lvm
  insmod diskfilter
  insmod mdraid1x
  insmod ext2
  insmod xfs
  search --no-floppy --fs-uuid --set=root 2559c296-413a-4f82-9882-de741aca022f
  linux /boot/reinstall/vmlinuz root=/dev/ram0 ramdisk_size=1500000 ip=100.64.100.100::100.64.0.1:255.255.0.0::enp1s0:static:100.64.255.254 url=http://local-install.vm/ubuntu-22.04-live-server-amd64.iso ds="nocloud-net;s=http://local-install.vm/"
  initrd  /boot/reinstall/initrd
}

menuentry 'Install without DNS support' {
  load_video
  gfxmode text
  insmod gzio
  insmod part_msdos
  insmod part_gpt
  insmod lvm
  insmod diskfilter
  insmod mdraid1x
  insmod ext2
  insmod xfs
  search --no-floppy --fs-uuid --set=root 2559c296-413a-4f82-9882-de741aca022f
  linux /boot/reinstall/vmlinuz root=/dev/ram0 ramdisk_size=1500000 ip=100.64.100.100::100.64.0.1:255.255.0.0::enp1s0:static url=http://100.64.241.175/ubuntu-22.04-live-server-amd64.iso ds="nocloud-net;s=http://100.64.241.175/"
  initrd  /boot/reinstall/initrd
}

user-data file:
#cloud-config
chpasswd:
  expire: false
  list:
    - installer:ubuntu-installer-22.04

meta-data is empty.

When running from  'Install with DNS support' http server logs shows:

local-install.vm 100.64.100.100 - - [27/Apr/2022:11:09:10 +0200] "GET /ubuntu-22.04-live-server-amd64.iso HTTP/1.1" 200 1466714112 "-" "Wget"
local-install.vm 100.64.100.100 - - [27/Apr/2022:11:09:18 +0200] "GET /ubuntu-22.04-live-server-amd64.iso HTTP/1.1" 200 1466714112 "-" "Cloud-Init/22.1-14-g2e17a0d6-0ubuntu1~22.04.5"
local-install.vm 100.64.100.100 - - [27/Apr/2022:11:09:18 +0200] "GET /meta-data HTTP/1.1" 200 0 "-" "Cloud-Init/22.1-14-g2e17a0d6-0ubuntu1~22.04.5"
local-install.vm 100.64.100.100 - - [27/Apr/2022:11:09:19 +0200] "GET /user-data HTTP/1.1" 200 87 "-" "Cloud-Init/22.1-14-g2e17a0d6-0ubuntu1~22.04.5"

ubuntu-22.04-live-server-amd64.iso is fetched twice. Once by wget
(casper phase?) and secound one by cloud-init.


But when running from 'Install without DNS support' I got this in the logs:

100.64.241.175 100.64.100.100 - - [27/Apr/2022:11:13:26 +0200] "GET /ubuntu-22.04-live-server-amd64.iso HTTP/1.1" 200 1466714112 "-" "Wget"
100.64.241.175 100.64.100.100 - - [27/Apr/2022:11:13:33 +0200] "GET /ubuntu-22.04-live-server-amd64.iso HTTP/1.1" 200 1466714112 "-" "Cloud-Init/22.1-14-g2e17a0d6-0ubuntu1~22.04.5"
100.64.241.175 100.64.100.100 - - [27/Apr/2022:11:13:36 +0200] "GET /ubuntu-22.04-live-server-amd64.iso HTTP/1.1" 200 1466714112 "-" "Cloud-Init/22.1-14-g2e17a0d6-0ubuntu1~22.04.5"
100.64.241.175 100.64.100.100 - - [27/Apr/2022:11:13:37 +0200] "GET /meta-data HTTP/1.1" 200 0 "-" "Cloud-Init/22.1-14-g2e17a0d6-0ubuntu1~22.04.5"
100.64.241.175 100.64.100.100 - - [27/Apr/2022:11:13:37 +0200] "GET /user-data HTTP/1.1" 200 87 "-" "Cloud-Init/22.1-14-g2e17a0d6-0ubuntu1~22.04.5"

ubuntu-22.04-live-server-amd64.iso is fetched  tree times (once by wget,
and two times by cloud-init).

I additonaly checked this with ubuntu-20.04.3-live-server-amd64.iso
(f8e3086f3cea0fb3fefb29937ab5ed9d19e767079633960ccb50e76153effc98) and
results are the same.

It's not big problem in LAN - but this is slow for insalling from remote
(Internet) location.

Best regards

** Affects: subiquity (Ubuntu)
     Importance: Undecided
         Status: New

-- 
The server installer double or triple fetches source ISO file
https://bugs.launchpad.net/bugs/1970595
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