edit

container/conf/web/nginx/conf.d/proxy.conf

@@ -8,7 +8,7 @@ server {
          proxy_pass  http://backend;
          proxy_redirect off;
          proxy_set_header        X-Forwarded-For $remote_addr;
-         location ~* \.(html|css|jpg|gif|ico|js)$ {
+         location ~* \.(html|css|jpg|gif|ico|js|png)$ {
                 proxy_cache          cache;
                 proxy_cache_key      $host$uri$is_args$args;
                 proxy_cache_valid    200 301 302 30m;