Description of problem:
I have been trying to build Fedora 35 packages with mock running on an EL8 host.
By default, mock is using systemd-nspawn.
There is an issue with name resolution from within the container.
Same issue with a Fedora 36 buildroot.
However, no issue with a Fedora 34 buildroot.
And indeed, no issue with name resolution on the EL8 host.

After hunting the issue with the fine folks from #fedora-buildsys, I've been instructed to file a bug against systemd, in the hope the issue will be routed to the proper component.


Version-Release number of selected component (if applicable):
systemd-239-45.el8_4.3.x86_64
Not sure which components NVR are relevant, let me know what's needed exactly, I'll fill in the blanks.

How reproducible:
Always

Steps to Reproduce:
1. sudo dnf install mock
2. usermod -G mock <some user>
3. mock -r fedora-35-x86_64 init

Actual results:
fedora                                                                                                                                                                                      0.0  B/s |   0  B     00:00    
Errors during downloading metadata for repository 'fedora':
  - Curl error (6): Couldn't resolve host name for https://mirrors.fedoraproject.org/metalink?repo=fedora-35&arch=x86_64 [getaddrinfo() thread failed to start]
Error: Failed to download metadata for repo 'fedora': Cannot prepare internal mirrorlist: Curl error (6): Couldn't resolve host name for https://mirrors.fedoraproject.org/metalink?repo=fedora-35&arch=x86_64 [getaddrinfo() thread failed to start]
ERROR: Command failed: 
 # /usr/bin/systemd-nspawn -q -M 7a694479a58649e48f2d3be341ebdbb4 -D /var/lib/mock/fedora-35-x86_64-bootstrap/root -a --capability=cap_ipc_lock --bind=/tmp/mock-resolv.7kr80qv4:/etc/resolv.conf --setenv=TERM=vt100 --setenv=SHELL=/bin/bash --setenv=HOME=/var/lib/mock/fedora-35-x86_64/root/installation-homedir --setenv=HOSTNAME=mock --setenv=PATH=/usr/bin:/bin:/usr/sbin:/sbin --setenv=PROMPT_COMMAND=printf "\033]0;<mock-chroot>\007" --setenv=PS1=<mock-chroot> \s-\v\$  --setenv=LANG=C.UTF-8 --setenv=LC_MESSAGES=C.UTF-8 --resolv-conf=off /usr/bin/dnf --installroot /var/lib/mock/fedora-35-x86_64/root/ --releasever 35 --setopt=deltarpm=False --allowerasing --disableplugin=local --disableplugin=spacewalk --disableplugin=versionlock install @buildsys-build
No matches found for the following disable plugin patterns: local, spacewalk, versionlock
fedora                                                                                                                                                                                      0.0  B/s |   0  B     00:00    
Errors during downloading metadata for repository 'fedora':
  - Curl error (6): Couldn't resolve host name for https://mirrors.fedoraproject.org/metalink?repo=fedora-35&arch=x86_64 [getaddrinfo() thread failed to start]
Error: Failed to download metadata for repo 'fedora': Cannot prepare internal mirrorlist: Curl error (6): Couldn't resolve host name for https://mirrors.fedoraproject.org/metalink?repo=fedora-35&arch=x86_64 [getaddrinfo() thread failed to start]


Expected results:
no error.

Additional info:
The workaround was to run mock with the '--isolation=simple' option, to avoid using the default '--isolation=nspawn'.