Hydra/zh-cn

Note: Hydra 旨在供 Nix/NixOS 软件包开发者使用；若仅是普通使用 NixOS，则不需要它。

Hydra 是一个用于持续集成测试和软件发布的工具，它使用一种纯函数式语言来描述构建作业及其依赖关系。持续集成是一种提高软件开发过程质量的简单技术。一个自动化系统会持续或定期地检出项目的源代码，进行构建、运行测试，并为开发人员生成报告。因此，可能意外提交到代码库中的各种错误都会被自动发现。

Hydra 官方服务器提供了预构建的二进制包，以加快 Nixpkgs 的更新速度：用户无需在自己的计算机上进行编译。

Hydra 手册 提供了 Hydra 功能与特性的概述，以及最新的安装指南。

安装

完整部署的启用过程同样非常简单：

  services.hydra = {
    enable = true;
    hydraURL = "http://localhost:3000"; # externally visible URL
    notificationSender = "hydra@localhost"; # e-mail of Hydra service
    # a standalone Hydra will require you to unset the buildMachinesFiles list to avoid using a nonexistant /etc/nix/machines
    buildMachinesFiles = [];
    # you will probably also want this, otherwise *everything* will be built from scratch
    useSubstitutes = true;
  };

如果你没有修改 services.hydra.dbi 选项，该模块会自动启用 postgresql。数据库结构会由 Hydra 服务自动创建；但请注意，部分状态数据会存储在数据库中，因此目前尚无法实现完全无状态的配置——请务必做好备份。

• 请参阅 nixos-option，或访问 NixOS 选项页面 以查看所有可用选项

网站配置

Hydra will provide the web interface at localhost port 3000. However you need to create a new admin user (as UNIX user hydra) before being able to perform any changes:

# su - hydra
$ hydra-create-user alice --full-name 'Alice Q. User' \
    --email-address 'alice@example.org' --password-prompt --role admin

虚拟机

如果未显式进行其他配置，Hydra 将默认使用 localhost 作为构建机。默认情况下，用于在虚拟机中执行构建的系统特性（如 “kvm” 或 “nixos-test”）不会被启用。此类作业将会无限期地处于排队状态。可以通过如下方式启用这些选项：

{
  nix.buildMachines = [
    { hostName = "localhost";
      protocol = null;
      system = "x86_64-linux";
      supportedFeatures = ["kvm" "nixos-test" "big-parallel" "benchmark"];
      maxJobs = 8;
    }
  ];
}

此选项会导致创建文件 /etc/nix/machines。若 Hydra 服务配置仍设置为 buildMachinesFiles = []，则该文件将被忽略，因此请移除此选项，或将 /etc/nix/machines 添加到该配置中。

Flake 作业集

按照如下方式配置作业集：

• Type: Flake

• Flake URI: an URI to a repo containing a Flake like git+https://git.myserver.net/user/repo.git

Flake 输出应包含属性 hydraJobs，其值为一个属性集；该属性集可包含嵌套结构，并可引用 derivation。

一个使 Hydra 构建所有软件包的示例 Flake 输出可能如下所示：

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  };
  outputs = { self, nixpkgs, ... }: {
    packages.x86_64-linux = {
      ...
    };

    hydraJobs = {
      inherit (self)
        packages;
    };
  };
}

受限模式

Hydra 会在 受限模式 下对 flakes 进行求值。此模式会阻止访问 nix store 之外的文件，包括作为 flake 输入获取的文件。请更新你的 nix.settings.allowed-uris，加入你预期用于获取 flake 输入的 URI 前缀：

nix.settings.allowed-uris = [
  "github:"
  "git+https://github.com/"
  "git+ssh://github.com/"
];

从 nixpkgs 构建单个软件包

Right now it is not possible to build a single package from nixpkgs with just that input. You will need to provide a supplementary repository which defines what to build. For examples you can check the hydra-example by makefu and in the Hydra Manual.

声明式构建

这些步骤是构建 hello 软件包所必需的。

1. 使用 hydra-create-user 创建用户后，登录 Hydra

1. 创建新项目

• identifier: example-hello

• display name: example-hello

1. Actions -> Create jobset

• identifier: hello

• Nix expression: release.nix in hydra-example -> will evaluate the file release.nix in the given input

• check interval: 60

• scheduling shares: 1

• Inputs:

Input Name	Type	Value	Note
nixpkgs	git checkout	https://github.com/nixos/nixpkgs nixos-21.11	will check out branch nixos-21.11, will be made available to the nix expression via <nixpkgs>.
hydra-example	git checkout	https://github.com/makefu/hydra-example	hydra-example is used by the jobset as input, release.nix is in the root directory

After creation, the jobset should be in the evaluation phase where inputs will be fetched. This phase may take some time as the complete nixpkgs repository needs to be downloaded before continuing. The result of the evaluation should be a single job which will get built.

Declarative Building

Since 2016, Hydra supports declarative creation of jobsets. Check out the example repository and description by Shea Levy.

Hydra Internals

Definitions

This subsection provides an overview of the Hydra-specific definitions and how to configure them.

Project

A cluster of Jobs which are all coming from a single input (like a git checkout), the first thing you will need to create. Every Job should be able to be built independently from another. Most of the time the project maps to a single repository like nixpkgs. It is comparable to the project definition in Jenkins.

Jobsets

A Jobset is a list of jobs which will be run. Often a jobset fits to a certain branch (master, staging, stable). A Jobset is defined by its inputs and will trigger if these inputs change. For example when a new commit onto a branch is added. Jobsets may depend on each other.

Job

A closure which will be built as part of a job set (like a single package, iso image or tarball).

Release Set

Defines all the jobs which are described in your release. By convention a file calledrelease.nix is being used. See the Hydra manual for Build Recipes for a thorough description of the structure.

Evaluation

The process of interpreting nix code into a list of .drv files. These files are the build recipes for all related outputs. You can introspect these files by running nix show-derivation nixpkgs.hello.

Build

Instantiation of a Job which is being triggered by being part of the release set.

Known Issues

• hydra-queue-runner sometimes gets stuck even with builds are in the queue, and the builds are not scheduled. The issue is being tracked here. In the meantime, a workaround is to add a cron job that regularly restarts the hydra-queue-runner systemd service. Possible fix: [1]

• If you see error: unexpected end-of-file it can mean multiple things, some of them are:

1. You have a miss-match between nix versions on the Hydra server and the builder

1. It can also mean that hydra-queue-runner needs privileges on the build server. Reference: [2]

• The default timeout for git operations is 600 seconds [3], which might cause fetches of large repositories like nixos/nixpkgs to fail: error fetching latest change from git repo at `https://github.com/nixos/nixpkgs': timeout. The timeout can be increased with the following configuration.nix snippet:

{
  services.hydra.extraConfig = ''
    <git-input>
      timeout = 3600
    </git-input>
  '';
}

Hydra for NixOS releases

Hydra is used for managing official Nix project releases. The project Hydra server: https://hydra.nixos.org/

Some Hydra trackers for Nix projects:

• Nixpkgs

• NixOS

Resources

• Video: Setting up a Hydra Build Farm by Peter Simons (2016)

• Hydra Caveats by Joepie91