Hi，

I want to introduce a proxy caching plugin, but there are several choices.

1. Based on Nginx's built-in proxy cache in ngx_http_proxy_module, it store data on disk.
2. Based on lua_shared_dict in ngx-lua-module, it store data on memory.
3. Based on external storage such as redis and other redis-like storage system.

Each option has its own scenario, but i think option 1 supports more functionality and less code needs to be implemented. In addition, I'd perfer to abstract these options into a plugin and then by parameters to distinguish.

What do you think of?