diff options
Diffstat (limited to 'nixpkgs/nixos/modules/services/misc/nix-daemon.nix')
-rw-r--r-- | nixpkgs/nixos/modules/services/misc/nix-daemon.nix | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/nixpkgs/nixos/modules/services/misc/nix-daemon.nix b/nixpkgs/nixos/modules/services/misc/nix-daemon.nix index ca59ea293783..2b21df91b82f 100644 --- a/nixpkgs/nixos/modules/services/misc/nix-daemon.nix +++ b/nixpkgs/nixos/modules/services/misc/nix-daemon.nix @@ -730,6 +730,40 @@ in }; restartTriggers = [ nixConf ]; + + # `stopIfChanged = false` changes to switch behavior + # from stop -> update units -> start + # to update units -> restart + # + # The `stopIfChanged` setting therefore controls a trade-off between a + # more predictable lifecycle, which runs the correct "version" of + # the `ExecStop` line, and on the other hand the availability of + # sockets during the switch, as the effectiveness of the stop operation + # depends on the socket being stopped as well. + # + # As `nix-daemon.service` does not make use of `ExecStop`, we prefer + # to keep the socket up and available. This is important for machines + # that run Nix-based services, such as automated build, test, and deploy + # services, that expect the daemon socket to be available at all times. + # + # Notably, the Nix client does not retry on failure to connect to the + # daemon socket, and the in-process RemoteStore instance will disable + # itself. This makes retries infeasible even for services that are + # aware of the issue. Failure to connect can affect not only new client + # processes, but also new RemoteStore instances in existing processes, + # as well as existing RemoteStore instances that have not saturated + # their connection pool. + # + # Also note that `stopIfChanged = true` does not kill existing + # connection handling daemons, as one might wish to happen before a + # breaking Nix upgrade (which is rare). The daemon forks that handle + # the individual connections split off into their own sessions, causing + # them not to be stopped by systemd. + # If a Nix upgrade does require all existing daemon processes to stop, + # nix-daemon must do so on its own accord, and only when the new version + # starts and detects that Nix's persistent state needs an upgrade. + stopIfChanged = false; + }; # Set up the environment variables for running Nix. |