Comment 2 for bug 2004130

I am in the same situation. None of our servers have internet access. Our APT sources point to a local Artifactory instance. No HTTPS proxy is in use.

$ systemctl --failed
  UNIT LOAD ACTIVE SUB DESCRIPTION
● esm-cache.service loaded failed failed Update the local ESM caches

LOAD = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB = The low-level unit activation state, values depend on unit type.

1 loaded units listed.

$ journalctl -o cat -u esm-cache.service
Starting Update the local ESM caches...
Traceback (most recent call last):
  File "/usr/lib/ubuntu-advantage/esm_cache.py", line 22, in <module>
    main(cfg)
  File "/usr/lib/ubuntu-advantage/esm_cache.py", line 11, in main
    update_esm_caches(cfg)
  File "/usr/lib/python3/dist-packages/uaclient/apt.py", line 636, in update_esm_caches
    cache.update()
  File "/usr/lib/python3/dist-packages/apt/cache.py", line 593, in update
    raise FetchFailedException()
apt.cache.FetchFailedException
esm-cache.service: Main process exited, code=exited, status=1/FAILURE
esm-cache.service: Failed with result 'exit-code'.
Failed to start Update the local ESM caches.

$ apt-cache policy ubuntu-advantage-tools
ubuntu-advantage-tools:
  Installed: 27.13.2~20.04.1
  Candidate: 27.13.2~20.04.1
  Version table:
 *** 27.13.2~20.04.1 500
        500 https://LOCALDOMAIN/artifactory/ubuntu-debian-remote focal-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     20.3 500
        500 https://LOCALDOMAIN/artifactory/ubuntu-debian-remote focal/main amd64 Packages

$ lsb_release -rd
Description: Ubuntu 20.04.5 LTS
Release: 20.04

$uname -a
Linux mail 5.4.0-137-generic #154-Ubuntu SMP Thu Jan 5 17:03:22 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux