Avoid unnecessary redirects

If you can not use symfony messenger, you can configure your webserver to avoid some redirects from the image controller. The solution described in this documentation only works when using the WebPathResolver, not when you store the images in a place outside of the web server.

When an image has not been cached, the imagine_filter generates the image link as a path to the image controller. The image controller creates the image and then redirects the client to the generated image.

By default, this redirection is done with status 302 (moved temporarily). This is important, because when you later clear the cache, the controller needs to be called again so that the image is regenerated. When returning 301, we tell the client that the resource moved permanently. The client will cache this information and directly request the (not existing) cached image even when the twig filter generates the controller URL again.

If you want to safely use 301 to avoid unnecessary redirects, you need to configure your webserver to route requests for missing images to Symfony.

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# bypass thumbs cache image files
location ~ ^/media/cache/resolve {
  expires 1M;
  access_log off;
  add_header Cache-Control "public";
  try_files $uri $uri/ /index.php?$query_string;
}

location ~* \.(js|jpg|jpeg|gif|png|css|tgz|gz|rar|bz2|doc|pdf|ppt|tar|wav|bmp|rtf|swf|ico|flv|txt|woff|woff2|svg)$ {
    expires 30d;
    add_header Pragma "public";
    add_header Cache-Control "public";
}

With such a configuration, you can safely set liip_imagine.controller.redirect_response_code to 301.

If you configure your web server like this, you can also use the imagine_filter_cache to never redirect your client.