We already set the relevant env vars in the systemd services. That does
not help one when executing any of the executables outside a service,
e.g. when creating a new user.
Also removed `pkgs.hydra-flakes` since flake-support has been merged
into master[1]. Because of that, `pkgs.hydra-unstable` is now compiled
against `pkgs.nixFlakes` and currently requires a patch since Hydra's
master doesn't compile[2] atm.
[1] https://github.com/NixOS/hydra/pull/730
[2] https://github.com/NixOS/hydra/pull/732
Upgrades Hydra to the latest master/flake branch. To perform this
upgrade, it's needed to do a non-trivial db-migration which provides a
massive performance-improvement[1].
The basic ideas behind multi-step upgrades of services between NixOS versions
have been gathered already[2]. For further context it's recommended to
read this first.
Basically, the following steps are needed:
* Upgrade to a non-breaking version of Hydra with the db-changes
(columns are still nullable here). If `system.stateVersion` is set to
something older than 20.03, the package will be selected
automatically, otherwise `pkgs.hydra-migration` needs to be used.
* Run `hydra-backfill-ids` on the server.
* Deploy either `pkgs.hydra-unstable` (for Hydra master) or
`pkgs.hydra-flakes` (for flakes-support) to activate the optimization.
The steps are also documented in the release-notes and in the module
using `warnings`.
`pkgs.hydra` has been removed as latest Hydra doesn't compile with
`pkgs.nixStable` and to ensure a graceful migration using the newly
introduced packages.
To verify the approach, a simple vm-test has been added which verifies
the migration steps.
[1] https://github.com/NixOS/hydra/pull/711
[2] https://github.com/NixOS/nixpkgs/pull/82353#issuecomment-598269471
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
This was originally removed in d4d0e449d7.
The intent was not to maintain hydra expression at two places.
Nowadays we have enough devs to maintain this despite copy/pasta.
This should encourage more people to use Hydra, which is a really
great piece of software together with Nix.
Tested a deploy using https://github.com/peti/hydra-tutorial
