building Nix...
building the system configuration...
updating GRUB 2 menu...
activating the configuration...
setting up /etc...
setting up tmpfiles
restarting the following units: nginx.service
the following new units were started: acme-gitlab.example.com.timer
warning: the following units failed: acme-gitlab.example.com.service

● acme-gitlab.example.com.service - Renew ACME Certificate for gitlab.example.com
   Loaded: loaded (/nix/store/dvpnwdfxbhrimj36vsdwgh7n3y8072vq-unit-acme-gitlab.example.com.service/acme-gitlab.example.com.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Sun 2017-09-10 22:04:28 CEST; 44ms ago
  Process: 19836 ExecStart=/nix/store/8jk0ns774mlgyjhcnkw9yb4pgy6xvrjd-unit-script/bin/acme-gitlab.example.com-start (code=exited, status=2)
  Process: 19819 ExecStartPre=/nix/store/dj9d74qy5xv0wdwmfbw9bknj3yvjpklj-unit-script/bin/acme-gitlab.example.com-pre-start (code=exited, status=0/SUCCESS)
 Main PID: 19836 (code=exited, status=2)

Sep 10 22:04:28 v24175 acme-gitlab.example.com-start[19836]:     ]
Sep 10 22:04:28 v24175 acme-gitlab.example.com-start[19836]:   ]
Sep 10 22:04:28 v24175 acme-gitlab.example.com-start[19836]: }
Sep 10 22:04:28 v24175 acme-gitlab.example.com-start[19836]: 2017-09-10 20:04:28,854:ERROR:simp_le:1271: CA marked some of the authorizations as invalid, which likely means it could not access http://example.com/.well-known/acme-challenge/X. Did you set correct path in -d example.com:path or --default_root? Is there a warning log entry about unsuccessful self-verification? Are all your domains accessible from the internet? Failing authorizations: https://acme-v01.api.letsencrypt.org/acme/authz/[redacted]...
Sep 10 22:04:28 v24175 acme-gitlab.example.com-start[19836]: Challenge validation has failed, see error log.
Sep 10 22:04:28 v24175 acme-gitlab.example.com-start[19836]: Debugging tips: -v improves output verbosity. Help is available under --help.
Sep 10 22:04:28 v24175 systemd[1]: acme-gitlab.example.com.service: Main process exited, code=exited, status=2/INVALIDARGUMENT
Sep 10 22:04:28 v24175 systemd[1]: Failed to start Renew ACME Certificate for gitlab.example.com.
Sep 10 22:04:28 v24175 systemd[1]: acme-gitlab.example.com.service: Unit entered failed state.
Sep 10 22:04:28 v24175 systemd[1]: acme-gitlab.example.com.service: Failed with result 'exit-code'.
Hint: Some lines were ellipsized, use -l to show in full.
warning: error(s) occurred while switching to the new configuration
nixos-rebuild switch  3.85s user 0.90s system 24% cpu 19.357 total