![]() The location directive for the frontend web server ( listen80) uses the proxy_pass directive to send requests prefixed with /img to the internally hosted responsive image server (127.0.0.1:9001). The max_size parameter defines the point at which NGINX Plus starts to remove the least recently requested images from the cache to make room for new cached items. The keys_zone parameter defines a shared memory zone for the cache index (called resized) and allocates 1 MB, which is sufficient for about 8,000 resized images. We start by defining the location of our cached images with the proxy_cache_path directive. Limit_req_zone "1" zone=2persec:32k rate=2r/s proxy_cache_path /var/www/imgcache levels=1 keys_zone=resized:1m max_size=256m The following configuration extends the configuration in Matching Image Size to Pixel Density by applying caching and rate limiting to the Image‑Filter module. To address this, we apply a rate limit to the responsive image server, but not to the frontend server containing the cached variants. Even with a relatively low volume of requests, such attacks may cause denial of service because of excessive CPU utilization. ![]() Having caching configured does not help if an attacker were to make rapid requests to unique image asset variants such as /img1001/mylogo.png, /img1002/mylogo.png, /img1003/mylogo.png and so on. We must also consider the security implications of allowing arbitrary requests to perform image resize operations. Production configuration of a responsive image server with caching enabled on the frontend web server We call this the responsive image server. We can achieve this with NGINX Plus configuration by defining a separate server that performs image resizing, and proxy requests to it only if the requested image size is not already in the cache. The most effective solution is to cache our resized image variants so that subsequent requests for each variant are served from the cache, without going through the Image‑Filter module. That is not good for overall latency and can also add significant CPU overhead. However, for a production environment we don’t want to wait for the web server to resize images for each request. The configuration described in Matching Image Size to Pixel Density can deliver any size variant of an image depending on the directory name used to request the image. Did you miss out on Part I? Click the link and check it out! Considerations for Production Use
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