Caching Middleman & Nginx

I recently setup a blog with Middleman served through Nginx. I always forget the best way to cache assets, so this is a nice reminder for me and anyone interested. In general you want to cache images, javascript, and css in the client users browser for a long time so no request has to be made. In nginx this is pretty simple to do

location ~* \.(?:ico|css|js|gif|jpe?g|png)$ {
  expires 30d; # expires after 30 days
  add_header Cache-Control "public"; # clients can cache

With Middleman you need a way to bust the cache, you can do this with fingerprints.

configure :build do
  activate :asset_hash

Now to test curl -I returns

HTTP/1.1 200 OK
Server: nginx/1.11.1
Date: Thu, 16 Jun 2016 01:33:18 GMT
Content-Type: image/png
Content-Length: 40257
Last-Modified: Thu, 16 Jun 2016 00:58:02 GMT
Connection: keep-alive
ETag: "5761f99a-9d41"
Expires: Sat, 16 Jul 2016 01:33:18 GMT
Cache-Control: max-age=2592000
Cache-Control: public
Accept-Ranges: bytes