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nixos-modules: Give the evaluator its own module - #1983
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The evaluator's service and settings lived in the web app's module, so the evaluator could only be configured along with the web app. Every other Rust service already has a module of its own: the queue runner, the builder, the websocket server and `hydra-ad-hoc`. The evaluator now does too, `evaluator-module.nix`, under `services.hydra-evaluator-dev`. This doesn't yet make it possible to run the evaluator elsewhere. Until more work is done it must be on the same machine as the web app: it runs Hydra's Perl, which reads the web app's `hydra.conf` and data directory, and it evaluates into the local Nix store. The module asserts this, and its `enable` defaults to the web app's, so existing deployments keep their evaluator. - The environment the web app's services share moves to `web-app-env.nix`, so that the evaluator module can use it too. - `services.hydra-dev.evaluatorSettings` and `minimumDiskFreeEvaluator` are renamed to `services.hydra-evaluator-dev.settings` and `minimumDiskFree`. - `services.hydra-dev.evaluatorExecutable` is replaced by `services.hydra-evaluator-dev.package`, matching the other modules. One behavior changes: changing `hydra.conf` no longer restarts the evaluator, killing any evaluation in progress. The restart dates from the C++ evaluator, which read `hydra.conf` once at startup. The Rust evaluator doesn't read it at all; only the Perl it runs does, and that starts afresh for each evaluation, so the next evaluation picks up the change. Assisted-by: Claude Code (Opus 5.5)
Ericson2314
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Oct 7, 2026
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I don't love needing this file, but if we get rid of plugins or redo them in Rust or whatever, then this goes away
Conni2461
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Oct 8, 2026
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thanks for doing the refactor. that aligns the setup more with the new queue runner :) changes look good to me. feel free to merge whenever
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Did this because @Conni2461 asked about it in #1940 (comment)
The evaluator's service and settings lived in the web app's module, so the evaluator could only be configured along with the web app. Every other Rust service already has a module of its own: the queue runner, the builder, the websocket server and
hydra-ad-hoc. The evaluator now does too,evaluator-module.nix, underservices.hydra-evaluator-dev.This doesn't yet make it possible to run the evaluator elsewhere. Until more work is done it must be on the same machine as the web app: it runs Hydra's Perl, which reads the web app's
hydra.confand data directory, and it evaluates into the local Nix store. The module asserts this, and itsenabledefaults to the web app's, so existing deployments keep their evaluator.The environment the web app's services share moves to
web-app-env.nix, so that the evaluator module can use it too.services.hydra-dev.evaluatorSettingsandminimumDiskFreeEvaluatorare renamed toservices.hydra-evaluator-dev.settingsandminimumDiskFree.services.hydra-dev.evaluatorExecutableis replaced byservices.hydra-evaluator-dev.package, matching the other modules.One behavior changes: changing
hydra.confno longer restarts the evaluator, killing any evaluation in progress. The restart dates from the C++ evaluator, which readhydra.confonce at startup. The Rust evaluator doesn't read it at all; only the Perl it runs does, and that starts afresh for each evaluation, so the next evaluation picks up the change.Assisted-by: Claude Code (Opus 5.5)