...

web1.....> Job for nginx.service failed because the control process exited with error code.
web1.....> See "systemctl status nginx.service" and "journalctl -xe" for details.
web1.....> error: Traceback (most recent call last):
  File "/nix/store/cpynzdmlns1lrywzfv2i2m0kpkppj75w-python2.7-nixops-1.6.1pre0_abcdef/lib/python2.7/site-packages/nixops/deployment.py", line 739, in worker
    raise Exception("unable to activate new configuration (exit code {})".format(res))
Exception: unable to activate new configuration (exit code 4)

Traceback (most recent call last):
  File "/nix/store/cpynzdmlns1lrywzfv2i2m0kpkppj75w-python2.7-nixops-1.6.1pre0_abcdef/bin/.nixops-wrapped", line 985, in <module>
    args.op()
  File "/nix/store/cpynzdmlns1lrywzfv2i2m0kpkppj75w-python2.7-nixops-1.6.1pre0_abcdef/bin/.nixops-wrapped", line 407, in op_deploy
    max_concurrent_activate=args.max_concurrent_activate)
  File "/nix/store/cpynzdmlns1lrywzfv2i2m0kpkppj75w-python2.7-nixops-1.6.1pre0_abcdef/lib/python2.7/site-packages/nixops/deployment.py", line 1059, in deploy
    self.run_with_notify('deploy', lambda: self._deploy(**kwargs))
  File "/nix/store/cpynzdmlns1lrywzfv2i2m0kpkppj75w-python2.7-nixops-1.6.1pre0_abcdef/lib/python2.7/site-packages/nixops/deployment.py", line 1048, in run_with_notify
    f()
  File "/nix/store/cpynzdmlns1lrywzfv2i2m0kpkppj75w-python2.7-nixops-1.6.1pre0_abcdef/lib/python2.7/site-packages/nixops/deployment.py", line 1059, in <lambda>
    self.run_with_notify('deploy', lambda: self._deploy(**kwargs))
  File "/nix/store/cpynzdmlns1lrywzfv2i2m0kpkppj75w-python2.7-nixops-1.6.1pre0_abcdef/lib/python2.7/site-packages/nixops/deployment.py", line 1015, in _deploy
    dry_activate=dry_activate, max_concurrent_activate=max_concurrent_activate)
  File "/nix/store/cpynzdmlns1lrywzfv2i2m0kpkppj75w-python2.7-nixops-1.6.1pre0_abcdef/lib/python2.7/site-packages/nixops/deployment.py", line 771, in activate_configs
    .format(len(failed), len(res), ", ".join(["‘{0}’".format(x) for x in failed])))
Exception: activation of 1 of 2 machines failed (namely on ‘web1’)