## Run your own Nixery

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- [0. Prerequisites](#0-prerequisites)
- [1. Choose a package set](#1-choose-a-package-set)
- [2. Build Nixery itself](#2-build-nixery-itself)
- [3. Prepare configuration](#3-prepare-configuration)
- [4. Deploy Nixery](#4-deploy-nixery)
- [5. Productionise](#5-productionise)

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⚠ This page is still under construction! ⚠

--------

Running your own Nixery is not difficult, but requires some setup. Follow the
steps below to get up & running.

*Note:* Nixery can be run inside of a [GKE][] cluster, providing a local service
from which images can be requested. Documentation for how to set this up is
forthcoming, please see [nixery#4][].

## 0. Prerequisites

To run Nixery, you must have:

* [Nix][] (to build Nixery itself)
* Somewhere to run it (your own server, Google AppEngine, a Kubernetes cluster,
  whatever!)
* *Either* a [Google Cloud Storage][gcs] bucket in which to store & serve layers,
  *or* a comfortable amount of disk space

Note that while the main Nixery process is a server written in Go,
it invokes a script that itself relies on Nix to be available.
You can compile the main Nixery daemon without Nix, but it won't
work without Nix.

(If you are completely new to Nix and don't know how to get
started, check the [Nix installation documentation][nixinstall].)

## 1. Choose a package set

When running your own Nixery you need to decide which package set you want to
serve. By default, Nixery builds packages from a recent NixOS channel which
ensures that most packages are cached upstream and no expensive builds need to
be performed for trivial things.

However if you are running a private Nixery, chances are high that you intend to
use it with your own packages. There are three options available:

1. Specify an upstream Nix/NixOS channel[^1], such as `nixos-20.09` or
   `nixos-unstable`.
2. Specify your own git-repository with a custom package set[^2]. This makes it
   possible to pull different tags, branches or commits by modifying the image
   tag.
3. Specify a local file path containing a Nix package set. Where this comes from
   or what it contains is up to you.

## 2. Build Nixery itself

### 2.1. With a container image

The easiest way to run Nixery is to build a container image. This
section assumes that the container runtime used is Docker, please
modify instructions accordingly if you are using something else.

With a working Nix installation, you can clone and build the Nixery
image like this:

```
git clone https://code.tvl.fyi/depot.git:/tools/nixery.git
nix-build -A nixery-image
```

This will create a `result`-symlink which points to a tarball containing the
image. In Docker, this tarball can be loaded by using `docker load -i result`.

### 2.2. Without a container image

*This method might be more convenient if you intend to work on
the code of the Nixery server itself, because you won't have to
rebuild (and reload) an image each time to test your changes.*

You will need to run the two following commands at the root of the repo:

* `go build` to build the `nixery` binary;
* `nix-env --install --file prepare-image/default.nix` to build
  the required helpers.

## 3. Prepare configuration

Nixery is configured via environment variables.

You must set *all* of these:

* `NIXERY_STORAGE_BACKEND` (must be set to `gcs` or `filesystem`)
* `PORT`: HTTP port on which Nixery should listen
* `WEB_DIR`: directory containing static files (see below)

You must set *one* of these:

* `NIXERY_CHANNEL`: The name of a [Nix/NixOS channel][nixchannel] to use for building,
  for instance `nixos-21.05`
* `NIXERY_PKGS_REPO`: URL of a git repository containing a package set (uses
  locally configured SSH/git credentials)
* `NIXERY_PKGS_PATH`: A local filesystem path containing a Nix package set to use
  for building

If `NIXERY_STORAGE_BACKEND` is set to `filesystem`, then `STORAGE_PATH`
must be set to the directory that will hold the registry blobs.
That directory must be located on a filesystem that supports extended
attributes (which means that on most systems, `/tmp` won't work).

If `NIXERY_STORAGE_BACKEND` is set to `gcs`, then `GCS_BUCKET`
must be set to the [Google Cloud Storage][gcs] bucket that will be
used to store & serve image layers.

You may set *all* of these:

* `NIX_TIMEOUT`: Number of seconds that any Nix builder is allowed to run
  (defaults to 60)

To authenticate to the configured GCS bucket, Nixery uses Google's [Application
Default Credentials][ADC]. Depending on your environment this may require
additional configuration.

If the `GOOGLE_APPLICATION_CREDENTIALS` environment is configured, the service
account's private key will be used to create [signed URLs for
layers][signed-urls].

## 4. Start Nixery

Run the image that was built in step 2.1 with all the environment variables
mentioned above. Alternatively, set all the environment variables and run
the Nixery server that was built in step 2.2.

Once Nixery is running you can immediately start requesting images from it.

## 5. Productionise

(⚠ Here be dragons! ⚠)

Nixery is still an early project and has not yet been deployed in any production
environments and some caveats apply.

Notably, Nixery currently does not support any authentication methods, so anyone
with network access to the registry can retrieve images.

Running a Nixery inside of a fenced-off environment (such as internal to a
Kubernetes cluster) should be fine, but you should consider to do all of the
following:

* Issue a TLS certificate for the hostname you are assigning to Nixery. In fact,
  Docker will refuse to pull images from registries that do not use TLS (with
  the exception of `.local` domains).
* Configure signed GCS URLs to avoid having to make your bucket world-readable.
* Configure request timeouts for Nixery if you have your own web server in front
  of it. This will be natively supported by Nixery in the future.

## 6. `WEB_DIR`

All the URLs accessed by Docker registry clients start with `/v2/`.
This means that it is possible to serve a static website from Nixery
itself (as long as you don't want to serve anything starting with `/v2`).
This is how, for instance, https://nixery.dev shows the website for Nixery,
while it is also possible to e.g. `docker pull nixery.dev/shell`.

When running Nixery, you must set the `WEB_DIR` environment variable.
When Nixery receives requests that don't look like registry requests,
it tries to serve them using files in the directory indicated by `WEB_DIR`.
If the directory doesn't exist, Nixery will run fine but serve 404.

-------

[^1]: Nixery will not work with Nix channels older than `nixos-19.03`.

[^2]: This documentation will be updated with instructions on how to best set up
    a custom Nix repository. Nixery expects custom package sets to be a superset
    of `nixpkgs`, as it uses `lib` and other features from `nixpkgs`
    extensively.

[GKE]: https://cloud.google.com/kubernetes-engine/
[nixery#4]: https://github.com/tazjin/nixery/issues/4
[Nix]: https://nixos.org/nix
[gcs]: https://cloud.google.com/storage/
[signed-urls]: under-the-hood.html#5-image-layers-are-requested
[ADC]: https://cloud.google.com/docs/authentication/production#finding_credentials_automatically
[nixinstall]: https://nixos.org/manual/nix/stable/installation/installing-binary.html
[nixchannel]: https://nixos.wiki/wiki/Nix_channels
