This applies [hydra PR #432](https://github.com/NixOS/hydra/pull/432)
to the NixOS module in nixpkgs:
```
commit 4efd078977e5ea20e1104783efc324cba11690bc
Author: Bas van Dijk <v.dijk.bas@gmail.com>
Date: Sun Dec 11 15:35:38 2016 +0100
Only set buildMachinesFiles when nix.buildMachines is defined
```
The following commit from 2016 in hydra removed the `--option
build-use-substitutes` from the hydra-queue-runner service:
```
commit ee2e9f5335c8c0288c102975b506f6b275793cfe
Author: Eelco Dolstra <edolstra@gmail.com>
Date: Fri Oct 7 20:23:05 2016 +0200
Update to reflect BinaryCacheStore changes
BinaryCacheStore no longer implements buildPaths() and ensurePath(),
so we need to use copyPath() / copyClosure().
```
It would be better if the hydra module in NixOS matches the upstream
module.
During the last update, `hydra-notify` was rewritten as a daemon which
listens to postgresql notifications for each build[1]. The module
uses the `hydra-notify.service` unit from upstream's Hydra module and
the VM test ensures that email notifications are sent properly.
Also updated `hydra-init.service` to install `pg_trgm` on a local
database if needed[2].
[1] c7861b85c4
[2] 8a0a5ec3a3
Currently there are two calls to curl in the reloadScript, neither which
check for errors. If something is misconfigured (like wrong authToken),
the only trace that something wrong happened is this log message:
Asking Jenkins to reload config
<h1>Bad Message 400</h1><pre>reason: Illegal character VCHAR='<'</pre>
The service isn't marked as failed, so it's easy to miss.
Fix it by passing --fail to curl.
While at it:
* Add $curl_opts and $jenkins_url variables to keep the curl command
lines DRY.
* Add --show-error to curl to show short error message explanation when
things go wrong (like HTTP 401 error).
* Lower-case the $CRUMB variable as upper case is for exported environment
variables.
The new behaviour, when having wrong accessToken:
Asking Jenkins to reload config
curl: (22) The requested URL returned error: 401
And the service is clearly marked as failed in `systemctl --failed`.
@cleverca found this bug in the declarative hooks config. Any shell
variables referenced in a hook script would get expanded by the hooks
directory builder.
Prevent variable expansion by quoting the here doc limit string.
Pass the -L flag to curl to make it follow redirects. This fixes an
issue I found when setting up reverse proxy for Jenkins. Without this
fix, the returned HTTP code was stuck at 302, making postStart fail the
service (it expects 200 or 403).
Also removes configText, functionality is now provided more conveniently by configOptions.
Keep in mind that this breaks compatibility with previous configurations,
configFile provides a means to protect the CI token from being written into the nix store.
The current behavior was for gitlab-runner is to immediately terminate when there
was a restart required. This can lead to aborted builds and is annoying to users.
By enabling graceful mode gitlab-runner will wait for all builds to finish before
terminating. The disadvantage is that a nixos-rebuild switch needs to wait till
all jobs are done. Because of that it is not enabled by default.