1 files changed, 171 insertions, 0 deletions
diff --git a/krebs/3modules/cachecache.nix b/krebs/3modules/cachecache.nix
new file mode 100644
index 000000000..989320480
--- /dev/null
+++ b/krebs/3modules/cachecache.nix
@@ -0,0 +1,171 @@
+{ config, lib, ... }:
+
+
+# fork of https://gist.github.com/rycee/f495fc6cc4130f155e8b670609a1e57b
+# related: https://github.com/nh2/nix-binary-cache-proxy
+
+with lib;
+
+let
+
+  cfg = config.krebs.cachecache;
+
+  nginxCfg = config.services.nginx;
+
+  cacheFallbackConfig = {
+    proxyPass = "$upstream_endpoint";
+    extraConfig = ''
+      # Default is HTTP/1, keepalive is only enabled in HTTP/1.1.
+      proxy_http_version 1.1;
+
+      # Remove the Connection header if the client sends it, it could
+      # be "close" to close a keepalive connection
+      proxy_set_header Connection "";
+
+      # Needed for CloudFront.
+      proxy_ssl_server_name on;
+
+      proxy_set_header Host $proxy_host;
+      proxy_cache nix_cache_cache;
+      proxy_cache_valid 200 302 60m;
+      proxy_cache_valid 404 1m;
+
+      expires max;
+      add_header Cache-Control $nix_cache_cache_header always;
+    '';
+  };
+
+in
+
+{
+  options = {
+    krebs.cachecache = {
+      enable = mkEnableOption "Nix binary cache cache";
+
+      virtualHost = mkOption {
+        type = types.str;
+        default = "nix-cache";
+        description = ''
+          Name of the nginx virtualhost to use and setup. If null, do
+          not setup any virtualhost.
+        '';
+      };
+      enableSSL = mkOption {
+        type = types.bool;
+        default = true;
+        description = ''
+          enable SSL via letsencrypt. Requires working dns resolution and open
+          internet tls port.
+        '';
+      };
+
+      # webRoot = mkOption {
+      #   type = types.str;
+      #   default = "/";
+      #   description = ''
+      #     Directory on virtual host that serves the cache. Must end in
+      #     <literal>/</literal>.
+      #   '';
+      # };
+
+      resolver = mkOption {
+        type = types.str;
+        description = "Address of DNS resolver.";
+        default = "8.8.8.8 ipv6=off";
+        example = "127.0.0.1 ipv6=off";
+      };
+
+      cacheDir = mkOption {
+        type = types.str;
+        default = "/var/cache/nix-cache-cache";
+        description = ''
+          Where nginx should store cached data.
+        '';
+      };
+
+      maxSize = mkOption {
+        type = types.str;
+        default = "50g";
+        description = "Maximum cache size.";
+      };
+    };
+  };
+
+  config = mkIf cfg.enable {
+    networking.firewall.allowedTCPPorts = [ 80 443 ];
+
+
+    systemd.services.nginx.preStart = ''
+      mkdir -p ${cfg.cacheDir} /srv/www/nix-cache-cache
+      chmod 700 ${cfg.cacheDir} /srv/www/nix-cache-cache
+      chown ${nginxCfg.user}:${nginxCfg.group} \
+        ${cfg.cacheDir} /srv/www/nix-cache-cache
+    '';
+
+    services.nginx = {
+      enable = true;
+
+      appendHttpConfig = ''
+        proxy_cache_path ${cfg.cacheDir}
+          levels=1:2
+          keys_zone=nix_cache_cache:100m
+          max_size=${cfg.maxSize}
+          inactive=365d
+          use_temp_path=off;
+
+        # Cache only success status codes; in particular we don't want
+        # to cache 404s. See https://serverfault.com/a/690258/128321.
+        map $status $nix_cache_cache_header {
+          200     "public";
+          302     "public";
+          default "no-cache";
+        }
+      '';
+
+      virtualHosts.${cfg.virtualHost} = {
+        addSSL = cfg.enableSSL;
+        enableACME = cfg.enableSSL;
+        extraConfig = ''
+          # Using a variable for the upstream endpoint to ensure that it is
+          # resolved at runtime as opposed to once when the config file is loaded
+          # and then cached forever (we don't want that):
+          # see https://tenzer.dk/nginx-with-dynamic-upstreams/
+          # This fixes errors like
+          #
+          #   nginx: [emerg] host not found in upstream "upstream.example.com"
+          #
+          # when the upstream host is not reachable for a short time when
+          # nginx is started.
+          resolver ${cfg.resolver} valid=10s;
+          set $upstream_endpoint https://cache.nixos.org;
+        '';
+
+        locations."/" =
+        {
+          root = "/srv/www/nix-cache-cache";
+          extraConfig = ''
+            expires max;
+            add_header Cache-Control $nix_cache_cache_header always;
+
+            # Ask the upstream server if a file isn't available
+            # locally.
+            error_page 404 = @fallback;
+
+            # Don't bother logging the above 404.
+            log_not_found off;
+          '';
+        };
+
+        locations."@fallback" = cacheFallbackConfig;
+
+        # We always want to copy cache.nixos.org's nix-cache-info
+        # file, and ignore our own, because `nix-push` by default
+        # generates one without `Priority` field, and thus that file
+        # by default has priority 50 (compared to cache.nixos.org's
+        # `Priority: 40`), which will make download clients prefer
+        # `cache.nixos.org` over our binary cache.
+        locations."= /nix-cache-info" = cacheFallbackConfig;
+      };
+    };
+  };
+}