**Note**: The instructions provided below are intended to enable new users to get a simple, local installation up and running. They are by no means sufficient for running a production server, let alone a public instance.
### Enabling The Service
Running Hydra is currently only supported on NixOS. The [hydra module](https://github.com/NixOS/nixpkgs/blob/release-20.03/nixos/modules/services/continuous-integration/hydra/default.nix) allows for an easy setup. The following configuration can be used for a simple setup that performs all builds on _localhost_ (Please refer to the [Options page](https://nixos.org/nixos/options.html#services.hydra) for all available options):
```nix
{
services.hydra = {
enable = true;
hydraURL = "http://localhost:3000";
notificationSender = "hydra@localhost";
buildMachinesFiles = [];
useSubstitutes = true;
};
}
```
### Creating An Admin User
Once the Hydra service has been configured as above and activate you should already be able to access the UI interface at the specified URL. However some actions require an admin user which has to be created first:
Afterwards you should be able to log by clicking on "_Sign In_" on the top right of the web interface using the credentials specified by `hydra-crate-user`. Once you are logged in you can click "_Admin -> Create Project_" to configure your first project.
In order to evaluate and build anything you need to crate _projects_ that contain _jobsets_. Hydra supports imperative and declarative projects and many different configurations. The steps below will guide you through the required steps to creating a minimal imperative project configuration.
#### Creating A Project
Log in as adminstrator, click "_Admin_" and select "_Create project_". Fill the form as follows:
- **Identifier**: `hello`
- **Display name**: `hello`
- **Description**: `hello project`
Click "_Create project_".
#### Creating A Jobset
After creating a project you are forwarded to the project page. Click "_Actions_" and choose "_Create jobset_". Fill the form with the following values:
- **Identifier**: `hello`
- **Nix expression**: `examples/hello.nix` in `hydra`
- **Check interval**: 60
- **Scheduling shares**: 1
We have to add two inputs for this jobset. One for _nixpkgs_ and one for _hydra_ (which we are referrencing in the Nix expression above):
Make sure **State** at the top of the page is set to "_Enabled_" and click on "_Create jobset_". This concludes the creation of a jobset that evaluates [./examples/hello.nix](./examples/hello.nix) once a minute. Clicking "_Evaluations_" should list the first evaluation of the newly created jobset after a brief delay.
When working on new features or bug fixes you want to be able to run Hydra from your working copy. There are
two ways to do this. One is better for interactive development and provides faster feedback cycles, the other
is more convenient for a single test run of Hydra from the working copy (suiteable for PR reviews).
#### Using runHydra
Hydra can be built and executed using the `runHydra` shell:
```
$ nix-shell default.nix -A runHydra
```
This will spawn a shell that starts hydra-server, hydra-queue-runner, hydra-evaluator and postgres using [foreman](https://github.com/ddollar/foreman).
In order to not collide with potentially existing installations running on default ports hydra and postgres are running on custom ports:
- hydra-server: 63333
- postgresql: 64444
**Note**: In some cases you may want to skip test execution. You can do so by passing `doCheck false`:
```
$ nix-shell default.nix -A runHydra --arg doCheck false
```
#### Using foreman
When you are actively working on the code, you need fast feedback cycles and thus want incremental builds. Instead of using
`runHydra` you can just run `foreman start` directly in the normal `nix-shell` environment:
You can also interface with Hydra through a JSON API. The API is defined in [hydra-api.yaml](./hydra-api.yaml) and you can test and explore via the [swagger editor](https://editor.swagger.io/?url=https://raw.githubusercontent.com/NixOS/hydra/master/hydra-api.yaml)
