npm registry caching proxy using nginx

npm_registry.conf

proxy_cache_path  /mnt/array1/nginx/cache  levels=1:2 keys_zone=STATIC:10m inactive=24h  max_size=1g;
proxy_temp_path   /mnt/array1/nginx/temp;

keepalive_timeout  2; 
tcp_nodelay        on;
sendfile        on;

limit_conn_zone $binary_remote_addr zone=addr:20m;
limit_req_zone $binary_remote_addr zone=req_per_ip:20m rate=80r/s;
limit_req zone=req_per_ip burst=100;

server {
    listen 1.2.3.4:80;
    listen 1.2.3.4:443;

    server_name registry.example.com;

    resolver 8.8.8.8;
    access_log /var/log/nginx/npm/access.log;
    error_log /var/log/nginx/npm/error.log;

    proxy_buffering on;

    # npm may fail to parse json if stricter limitation is applied
    limit_conn addr 50;

    location / {

        sub_filter    registry.npmjs.org       registry.example.com;
        sub_filter_once off;
        sub_filter_types application/json;

        proxy_pass $scheme://registry.npmjs.org;
        proxy_bind 2.3.4.5;  # cross the GFW

        proxy_set_header Host "registry.npmjs.org";
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;

        proxy_cache STATIC;
        proxy_cache_valid   404  1m;
        proxy_cache_use_stale error timeout invalid_header updating http_500 http_502 http_503 http_504;
    }
}