nginx: use proxy_store for tarballs

Since tarballs are never supposed to change and because we will
eventually want a method of pre-seeding a registry, switch to a
combination of try_files and proxy_store for the tarballs instead of
using a real cache.

Note that this _does_ have implications on disk usage of long-running
instances since infrequently used tarballs will never be removed.

Author: rmg

nginx.conf

@@ -42,14 +42,8 @@ http {
             return upstream
         }
         location ~ ^/.*\.tgz$ {
-            resolver               127.0.0.1 ipv6=off;
-            proxy_pass             $npm_config_registry;
-            proxy_cache            NPM;
-            proxy_ignore_headers   X-Accel-Redirect X-Accel-Expires X-Accel-Limit-Rate X-Accel-Buffering X-Accel-Charset Expires Cache-Control Set-Cookie Vary;
-            # npm package tarballs are NEVER supposed to change
-            proxy_cache_revalidate off;
-            proxy_cache_valid      200  90d;
-            proxy_cache_use_stale  error timeout invalid_header updating http_500 http_502 http_503 http_504;
+            root               /tmp/npm/store;
+            try_files          $uri @fetch-tgz;
         }
         location / {
             resolver               127.0.0.1 ipv6=off;
@@ -77,5 +71,14 @@ http {
                 ngx.arg[1] = string.gsub(ngx.arg[1], upstream, base)
             }
         }
+        location @fetch-tgz {
+            internal;
+            resolver           127.0.0.1 ipv6=off;
+            proxy_pass         $npm_config_registry;
+            proxy_store        on;
+            proxy_store_access user:rw group:rw all:r;
+            proxy_temp_path    /tmp/npm/temp;
+            root               /tmp/npm/store;
+        }
     }
 }