hydra/doc/manual/src/configuration.md

Configuration

This chapter is a collection of configuration snippets for different scenarios.

The configuration is parsed by Config::General which has a pretty thorough documentation on their file format. Hydra calls the parser with the following options:

• -UseApacheInclude => 1
• -IncludeAgain => 1
• -IncludeRelative => 1

Including files

hydra.conf supports Apache-style includes. This is IMPORTANT because that is how you keep your secrets out of the Nix store. Hopefully this got your attention 😌

This:

<github_authorization>
NixOS = Bearer gha-secret😱secret😱secret😱
</github_authorization>

should NOT be in hydra.conf.

hydra.conf is rendered in the Nix store and is therefore world-readable.

Instead, the above should be written to a file outside the Nix store by other means (manually, using Nixops' secrets feature, etc) and included like so:

Include /run/keys/hydra/github_authorizations.conf

Serving behind reverse proxy

To serve hydra web server behind reverse proxy like nginx or httpd some additional configuration must be made.

Edit your hydra.conf file in a similar way to this example:

using_frontend_proxy 1
base_uri example.com

base_uri should be your hydra servers proxied URL. If you are using Hydra nixos module then setting hydraURL option should be enough.

If you want to serve Hydra with a prefix path, for example http://example.com/hydra then you need to configure your reverse proxy to pass X-Request-Base to hydra, with prefix path as value. For example if you are using nginx, then use configuration similar to following:

server {
    listen 433 ssl;
    server_name example.com;
    .. other configuration ..
    location /hydra/ {

        proxy_pass     http://127.0.0.1:3000;
        proxy_redirect http://127.0.0.1:3000 https://example.com/hydra;

        proxy_set_header  Host              $host;
        proxy_set_header  X-Real-IP         $remote_addr;
        proxy_set_header  X-Forwarded-For   $proxy_add_x_forwarded_for;
        proxy_set_header  X-Forwarded-Proto $scheme;
        proxy_set_header  X-Request-Base    /hydra;
    }
}

Populating a Cache

A common use for Hydra is to pre-build and cache derivations which take a long time to build. While it is possible to direcly access the Hydra server's store over SSH, a more scalable option is to upload built derivations to a remote store like an S3-compatible object store. Setting the store_uri parameter will cause Hydra to sign and upload derivations as they are built:

store_uri = s3://cache-bucket-name?compression=zstd&parallel-compression=true&write-nar-listing=1&ls-compression=br&log-compression=br&secret-key=/path/to/cache/private/key

This example uses Zstandard compression on derivations to reduce CPU usage on the server, but Brotli compression for derivation listings and build logs because it has better browser support.

See nix help stores for a description of the store URI format.

Statsd Configuration

By default, Hydra will send stats to statsd at localhost:8125. Point Hydra to a different server via:

<statsd>
  host = alternative.host
  port = 18125
</statsd>

hydra-notify's Prometheus service

hydra-notify supports running a Prometheus webserver for metrics. The exporter does not run unless a listen address and port are specified in the hydra configuration file, as below:

<hydra_notify>
  <prometheus>
    listen_address = 127.0.0.1
    port = 9199
  </prometheus>
</hydra_notify>

hydra-queue-runner's Prometheus service

hydra-queue-runner supports running a Prometheus webserver for metrics. The exporter's address defaults to exposing on 127.0.0.1:9198, but is also configurable through the hydra configuration file and a command line argument, as below. A port of :0 will make the exposer choose a random, available port.

queue_runner_metrics_address = 127.0.0.1:9198
# or
queue_runner_metrics_address = [::]:9198

$ hydra-queue-runner --prometheus-address 127.0.0.1:9198
# or
$ hydra-queue-runner --prometheus-address [::]:9198

Using LDAP as authentication backend (optional)

Instead of using Hydra's built-in user management you can optionally use LDAP to manage roles and users.

This is configured by defining the <ldap> block in the configuration file. In this block it's possible to configure the authentication plugin in the <config> block. All options are directly passed to Catalyst::Authentication::Store::LDAP. The documentation for the available settings can be found here.

Note that the bind password (if needed) should be supplied as an included file to prevent it from leaking to the Nix store.

Roles can be assigned to users based on their LDAP group membership. For this to work use_roles = 1 needs to be defined for the authentication plugin. LDAP groups can then be mapped to Hydra roles using the <role_mapping> block.

Example configuration:

<ldap>
  <config>
    <credential>
      class = Password
      password_field = password
      password_type = self_check
    </credential>
    <store>
      class = LDAP
      ldap_server = localhost
      <ldap_server_options>
        timeout = 30
      </ldap_server_options>
      binddn = "cn=root,dc=example"
      include ldap-password.conf
      start_tls = 0
      <start_tls_options>
        verify = none
      </start_tls_options>
      user_basedn = "ou=users,dc=example"
      user_filter = "(&(objectClass=inetOrgPerson)(cn=%s))"
      user_scope = one
      user_field = cn
      <user_search_options>
        deref = always
      </user_search_options>
      # Important for role mappings to work:
      use_roles = 1
      role_basedn = "ou=groups,dc=example"
      role_filter = "(&(objectClass=groupOfNames)(member=%s))"
      role_scope = one
      role_field = cn
      role_value = dn
      <role_search_options>
        deref = always
      </role_search_options>
    </store>
  </config>
  <role_mapping>
    # Make all users in the hydra_admin group Hydra admins
    hydra_admin = admin
    # Allow all users in the dev group to restart jobs and cancel builds
    dev = restart-jobs
    dev = cancel-build
  </role_mapping>
</ldap>

Then, place the password to your LDAP server in /var/lib/hydra/ldap-password.conf:

bindpw = the-ldap-password

Debugging LDAP

Set the debug parameter under ldap.config.ldap_server_options.debug:

<ldap>
  <config>
    <store>
      <ldap_server_options>
        debug = 2
      </ldap_server_options>
    </store>
  </config>
</ldap>

Legacy LDAP Configuration

Hydra used to load the LDAP configuration from a YAML file in the HYDRA_LDAP_CONFIG environment variable. This behavior is deperecated and will be removed.

When Hydra uses the deprecated YAML file, Hydra applies the following default role mapping:

<ldap>
  <role_mapping>
    hydra_admin = admin
    hydra_bump-to-front = bump-to-front
    hydra_cancel-build = cancel-build
    hydra_create-projects = create-projects
    hydra_restart-jobs = restart-jobs
  </role_mapping>
</ldap>

Note that configuring both the LDAP parameters in the hydra.conf and via the environment variable is a fatal error.

Embedding Extra HTML

Embed an analytics widget or other HTML in the <head> of each HTML document via:

tracker = <script src="...">