add nix/nixos deployment documentation

.gitlab/CODEOWNERS

@@ -2,3 +2,4 @@
 .envrc @CobaltCause
 flake.lock @CobaltCause
 flake.nix @CobaltCause
+nix/ @CobaltCause

README.md

@@ -34,6 +34,7 @@ Check out the [Conduit 1.0 Release Milestone](https://gitlab.com/famedly/conduit
 
 - Simple install (this was tested the most): [DEPLOY.md](DEPLOY.md)
 - Debian package: [debian/README.Debian](debian/README.Debian)
+- Nix/NixOS: [nix/README.md](nix/README.md)
 - Docker: [docker/README.md](docker/README.md)
 
 If you want to connect an Appservice to Conduit, take a look at [APPSERVICES.md](APPSERVICES.md).

nix/README.md

@@ -0,0 +1,188 @@
+# Conduit for Nix/NixOS
+
+This guide assumes you have a recent version of Nix (^2.4) installed.
+
+Since Conduit ships as a Nix flake, you'll first need to [enable
+flakes][enable_flakes].
+
+You can now use the usual Nix commands to interact with Conduit's flake. For
+example, `nix run gitlab:famedly/conduit` will run Conduit (though you'll need
+to provide configuration and such manually as usual).
+
+If your NixOS configuration is defined as a flake, you can depend on this flake
+to provide a more up-to-date version than provided by `nixpkgs`. In your flake,
+add the following to your `inputs`:
+
+```nix
+conduit = {
+    url = "gitlab:famedly/conduit";
+
+    # Assuming you have an input for nixpkgs called `nixpkgs`. If you experience
+    # build failures while using this, try commenting/deleting this line. This
+    # will probably also require you to always build from source.
+    inputs.nixpkgs.follows = "nixpkgs";
+};
+```
+
+Next, make sure you're passing your flake inputs to the `specialArgs` argument
+of `nixpkgs.lib.nixosSystem` [as explained here][specialargs]. This guide will
+assume you've named the group `flake-inputs`.
+
+Now you can configure Conduit and a reverse proxy for it. Add the following to
+a new Nix file and include it in your configuration:
+
+```nix
+{ config
+, pkgs
+, flake-inputs
+, ...
+}:
+
+let
+  # You'll need to edit these values
+
+  # The hostname that will appear in your user and room IDs
+  server_name = "example.com";
+
+  # The hostname that Conduit actually runs on
+  #
+  # This can be the same as `server_name` if you want. This is only necessary
+  # when Conduit is running on a different machine than the one hosting your
+  # root domain. This configuration also assumes this is all running on a single
+  # machine, some tweaks will need to be made if this is not the case.
+  matrix_hostname = "matrix.${server_name}";
+
+  # An admin email for TLS certificate notifications
+  admin_email = "admin@${server_name}";
+
+  # These ones you can leave alone
+
+  # Build a dervation that stores the content of `${server_name}/.well-known/matrix/server`
+  well_known_server = pkgs.writeText "well-known-matrix-server" ''
+    {
+      "m.server": "${matrix_hostname}"
+    }
+  '';
+
+  # Build a dervation that stores the content of `${server_name}/.well-known/matrix/client`
+  well_known_client = pkgs.writeText "well-known-matrix-client" ''
+    {
+      "m.homeserver": {
+        "base_url": "https://${matrix_hostname}"
+      }
+    }
+  '';
+in
+
+{
+  # Configure Conduit itself
+  services.matrix-conduit = {
+    enable = true;
+
+    # This causes NixOS to use the flake defined in this repository instead of
+    # the build of Conduit built into nixpkgs.
+    package = flake-inputs.conduit.packages.${pkgs.system}.default;
+
+    settings.global = {
+      inherit server_name;
+    };
+  };
+
+  # Configure automated TLS acquisition/renewal
+  security.acme = {
+    acceptTerms = true;
+    defaults = {
+      email = admin_email;
+    };
+  };
+
+  # ACME data must be readable by the NGINX user
+  users.users.nginx.extraGroups = [
+    "acme"
+  ];
+
+  # Configure NGINX as a reverse proxy
+  services.nginx = {
+    enable = true;
+    recommendedProxySettings = true;
+
+    virtualHosts = {
+      "${server_name}" = {
+        forceSSL = true;
+        enableACME = true;
+
+        listen = [
+          {
+            addr = "0.0.0.0";
+            port = 443;
+            ssl = true;
+          }
+          {
+            addr = "0.0.0.0";
+            port = 8448;
+            ssl = true;
+          }
+        ];
+
+        extraConfig = ''
+          merge_slashes off;
+        '';
+
+      "${matrix_hostname}" = {
+        forceSSL = true;
+        enableACME = true;
+
+        locations."/_matrix/" = {
+          proxyPass = "http://backend_conduit$request_uri";
+          proxyWebsockets = true;
+          extraConfig = ''
+            proxy_set_header Host $host;
+            proxy_buffering off;
+          '';
+        };
+
+        locations."=/.well-known/matrix/server" = {
+          # Use the contents of the derivation built previously
+          alias = "${well_known_server}";
+
+          extraConfig = ''
+            # Set the header since by default NGINX thinks it's just bytes
+            default_type application/json;
+          '';
+        };
+
+        locations."=/.well-known/matrix/client" = {
+          # Use the contents of the derivation built previously
+          alias = "${well_known_client}";
+
+          extraConfig = ''
+            # Set the header since by default NGINX thinks it's just bytes
+            default_type application/json;
+
+            # https://matrix.org/docs/spec/client_server/r0.4.0#web-browser-clients
+            add_header Access-Control-Allow-Origin "*";
+          '';
+        };
+      };
+    };
+
+    upstreams = {
+      "backend_conduit" = {
+        servers = {
+          "localhost:${toString config.services.matrix-conduit.settings.global.port}" = { };
+        };
+      };
+    };
+  };
+
+  # Open firewall ports for HTTP, HTTPS, and Matrix federation
+  networking.firewall.allowedTCPPorts = [ 80 443 8448 ];
+  networking.firewall.allowedUDPPorts = [ 80 443 8448 ];
+}
+```
+
+Now you can rebuild your system configuration and you should be good to go!
+
+[enable_flakes]: https://nixos.wiki/wiki/Flakes#Enable_flakes
+
+[specialargs]: https://nixos.wiki/wiki/Flakes#Using_nix_flakes_with_NixOS