cluster/services/ways: support multiple backends via consul services

cluster/services/ways/host.nix

@@ -1,13 +1,18 @@
-{ cluster, depot, lib, ... }:
+{ cluster, config, depot, lib, pkgs, ... }:
 
 let
   inherit (depot.lib.meta) domain;
 
   externalWays = lib.filterAttrs (_: cfg: !cfg.internal) cluster.config.ways;
+
+  consulServiceWays = lib.filterAttrs (_: cfg: cfg.useConsul) cluster.config.ways;
+
+  consulHttpAddr = "${config.services.consul.extraConfig.addresses.http or "127.0.0.1"}:${toString (config.services.consul.extraConfig.ports.http or 8500)}";
 in
 
 {
-  services.nginx.virtualHosts = lib.mapAttrs' (name: cfg: {
+  services.nginx = {
+    virtualHosts = lib.mapAttrs' (name: cfg: {
       name = if cfg.internal then "${name}.internal.${domain}" else "${name}.${domain}";
       value = { ... }: {
         imports = [
@@ -33,6 +38,11 @@ in
       };
     }) cluster.config.ways;
 
+    appendHttpConfig = lib.mkIf (consulServiceWays != {}) ''
+      include /run/consul-template/nginx-ways-*.conf;
+    '';
+  };
+
   security.acme.certs = lib.mapAttrs' (name: cfg: {
     name = "${name}.${domain}";
     value = {
@@ -41,6 +51,33 @@ in
     };
   }) externalWays;
 
+  services.consul-template.instances.ways = lib.mkIf (consulServiceWays != {}) {
+    user = "nginx";
+    group = "nginx";
+    settings = {
+      consul.address = "http://${consulHttpAddr}";
+      template = [
+        {
+          source = let
+            upstreams = lib.mapAttrsToList (_: cfg: ''
+              upstream ${cfg.nginxUpstreamName} {
+                {{ range $i, $e := service "${cfg.consulService}~_agent" -}}
+                server {{ .Address }}:{{ .Port }}{{ if ne $i 0 }} backup{{ end }};
+                {{end}}
+              }
+            '') consulServiceWays;
+          in pkgs.writeText "ways-upstreams.ctmpl" (lib.concatStringsSep "\n" upstreams);
+          destination = "/run/consul-template/nginx-ways-upstreams.conf";
+          exec.command = [
+            "${config.services.nginx.package}/bin/nginx"
+            "-s" "reload"
+            "-g" "pid /run/nginx/nginx.pid;"
+          ];
+        }
+      ];
+    };
+  };
+
   consul.services.ways-proxy = {
     unit = "nginx";
     mode = "external";

cluster/services/ways/options/way.nix

@@ -1,4 +1,4 @@
-{ lib, name, ... }:
+{ lib, name, options, ... }:
 
 with lib;
 
@@ -20,15 +20,38 @@ with lib;
       type = types.str;
     };
 
+    consulService = mkOption {
+      type = types.str;
+    };
+
     healthCheckPath = mkOption {
       type = types.path;
       default = "/.well-known/ways/internal-health-check";
     };
 
+    useConsul = mkOption {
+      type = types.bool;
+      internal = true;
+      default = false;
+    };
+
+    nginxUpstreamName = mkOption {
+      type = types.str;
+      internal = true;
+    };
+
     extras = mkOption {
       description = "Extra configuration to pass to the nginx virtual host submodule.";
       type = types.deferredModule;
       default = {};
     };
   };
+
+  config = lib.mkMerge [
+    (lib.mkIf options.consulService.isDefined {
+      useConsul = true;
+      nginxUpstreamName = "ways_upstream_${builtins.hashString "md5" options.consulService.value}";
+      target = "http://${options.nginxUpstreamName.value}";
+    })
+  ];
 }