Nginx resize with invalidation after change source image

etag_resize.js

function etag_resize (r) {
  function done (r2) {
    // Extract etag header
    var source_etag = r2.headersOut.etag
    // Pass variables from location
    var width = r.variables.width
    var height = r.variables.height
    var image_path = r.variables.image_path
    var convert_path = r.variables.convert_path || '/_ei/'
    // construct resize with cache url
    var path = `${convert_path}${image_path}?width=${width}&height=${height}&source_etag=${source_etag}`
    r.internalRedirect(path)
  }
  r.subrequest(r.variables.image_path, { method: 'HEAD' }, done)
}

nginx.conf

# We need njs and image_filter module. Also avaiable on docker image `nginx:1.17`

load_module /etc/nginx/modules/ngx_http_image_filter_module.so;
load_module /etc/nginx/modules/ngx_http_js_module.so;


http {
    # .. other setting default
    
    proxy_cache_path /nginx-data/resize/ levels=1:2 keys_zone=resize_images:512m inactive=30d max_size=10G;

    # Important!
    js_include etag_resize.js;

    server {
      listen 80;
      server_name _;

      location /media {
            # Etag  must be enabled!
            etag on;
            alias /public/media/;
            # TODO cache
            expires 1y;
            # access_log off;
            add_header Vary Accept-Encoding;
            add_header Cache-Control public;
      }


      location ~* '^/i/(\d+)x(\d+)/(.*)$' {
        # https://example.org/i/<width>x<height>/path/to/image.png
        set $width  $1;
        set $height $2;
        set $image_path /$3;
        js_content etag_resize;
      }
      location ~* '^/i/w(\d+)/(.*)$' {
        # https://example.org/i/w<width>/path/to/image.png
        set $width  $1;
        set $height "-";
        set $image_path /$2;
        js_content etag_resize;
      }

      location ~* '^/i/h(\d+)/(.*)$' {
        # https://example.org/i/w<width>/path/to/image.png
        set $width  "-";
        set $height $1;
        set $image_path /$2;
        js_content etag_resize;
      }

      location ~* '^/i/(.*)$' {
        # https://example.org/i/path/to/image.png
        set $width 100;
        set $height 100;
        set $image_path /$1;
        js_content etag_resize;
      }

      location /_ei/ {
        # Based by https://gist.github.com/phpdude/1451684
         
        # Magic from
        # https://stackoverflow.com/questions/28684300/nginx-pass-proxy-subdirectory-without-url-decoding/37584637    
        rewrite ^ $request_uri;
        rewrite ^/_ei/(.*) $1 break;
        # End magic
            
        root /nginx-data/resize/;
        set $width $arg_width;
        set $height $arg_height;
        set $source_etag $arg_source_etag;
        if ($source_etag ~* '^"(.*)"$') {
            set $source_etag $1;
        }

        if ($uri ~* "^/_ei/(.*)" ) {
            set $image_path $1;
        }
        if ($image_path ~* "^.*\.(.*)$") {
            set $ext $1;
        }

        set $image_uri __resize/$image_path?width=$width&height=$height;
        set $resize_status 'no';
        set $image_store_path "$image_path/$source_etag/${width}x${height}.$ext";
        set $abs_image_store_path "/nginx-data/resize$image_store_path";

        if (!-f $abs_image_store_path) {
            proxy_pass http://127.0.0.1:80/$image_uri;
            set $resize_status 'yes';
            break;
        }

        proxy_store $abs_image_store_path;
        proxy_store_access   user:rw  group:rw  all:r;
        proxy_temp_path      /tmp/images;
        # For debug
        add_header X-Filename $abs_image_store_path;
        add_header X-Resize-Status $resize_status;
        add_header X-Source-Etag $source_tag;


        expires 1y;
        access_log off;
        add_header Vary Accept-Encoding;
        add_header Cache-Control public;

        rewrite ^(.*)$ $image_store_path break;
      }

      location /__resize/ {
        alias /public/;
        image_filter_buffer 50M;
        image_filter resize $arg_width $arg_height;
        image_filter_jpeg_quality 75;
        allow 127.0.0.0/8;
        deny all;
      }
    }

}