On-the-fly image converting, file size reduction and caching by apache2 reverse proxy and software 'imageproxy'

By reducing image quality one can reduce image size enormously. When using a content management system there is the disadventage that users often can upload images from camera or smartphone with original size directly.
Thus for a 1024x800 pixel image on the webpage a 9MB image is upload without resizing or other image processing.

To save mobile bandwith you can reduce image file size by shrinking image quality. Normally users do not notice a reduced image quality.

For this porpos you can use the imageproxy https://github.com/willnorris/imageproxy (written in go) that runs as a standalone application on linux. The imageproxy is cabable of interacting with apache2 by url encoded paramters.

           www.mycompany.test

             +------------+   
             |   Reverse  +--------------- backend webserver 1
User  >------+    Proxy   + 
             |      ^     +--------------- backend webserver 2
             |      |     |
             |      v     |
             | +--------+ |
             | | Image  | |
             | | Proxy  | |
             | +--------+ |
             +------------+   

The imageproxy runs on localhost and takes its paramter by url: imageproxy URLs are of the form: http://localhost:4593/{options}/{remote_url}

The imageproxy cames as a linux service:

# service  imageproxy status
# service  imageproxy stop
# service  imageproxy start
# /usr/local/go/src/willnorris.com/go/imageproxy/etc/imageproxy.service

I am using this service file:

# This is the systemd config I use for https://willnorris.com/api/imageproxy/
[Unit]
Description=Image Proxy
Documentation=https://github.com/willnorris/imageproxy
PartOf=Network.target
After=local-fs.target  network-online.target
Wants = network-online.target


[Service]
User=www-data
ExecStart=/usr/local/go/bin/imageproxy -addr localhost:4593 -cache memory:2000:72h -cache directory /var/spool/imageproxy  -baseURL https://www.mycompany.test/
Restart=on-abort
StandardOutput=syslog
StandardError=syslog
SyslogIdentifier=imageproxy

[Install]
WantedBy=multi-user.target
Alias=imageproxy.service

The workflow to control image size is defined by some apache2 rewrite rule:

If a image ends with the suffix .jpg, .gif or .png  
AND the request is not from localhost or webserver's IP 
AND the webbrowser is mobile (or a maybe a spider)
THEN the request is redirected to imageproxy

ELSE the image is on the server and pass through to the imageproxy  

# For requests from mobile devices:
RewriteCond %{REQUEST_URI}      ^(.*)\.(jpg|gif|png)$   [NC]
RewriteCond %{REMOTE_ADDR}      !^147\.142\.106\.210$
RewriteCond %{REMOTE_ADDR}      !^127\.0\.0\.1$
RewriteCond %{HTTP_USER_AGENT} (android|bb\d+|meego).+mobile|avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od)|iris|kindle|lge\ |maemo|midp|mmp|mobile.+firefox|netfront|opera\ m(ob|in)i|palm(\ os)?|phone|p(ixi|re)\/|plucker|pocket|psp|series(4|6)0|symbian|treo|up\.(browser|link)|vodafone|wap|windows\ ce|xda|xiino                             [NC]
RewriteRule ^(.*)$  http://localhost:4593/q50/https://www.mycompany.test%{REQUEST_URI} [P,L]

[...]

# If this is a reverse proxy only then you do have a second forward otherwise the image is in document root 
# RewriteRule ^/images/(.*)$   https://images.mycompany.test/images/$1 [P,L]
# OR
# RewriteCond %{REQUEST_URI}      ^(.*)\.(jpg|gif|png)$   [NC]
# RewriteRule ^(.*)$   https://images.mycompany.test/$1 [P,L]

If you want to exclude images from filesize shrinking, you can do this by:

# by single file
RewriteCond %{REQUEST_URI}      !^(.*)/topframeimage_HD\.jpg$   [NC]

# or by complete directory
RewriteCond %{REQUEST_URI}      !^(.*)/HDImages/(.*)$   [NC]

Theses are the workflow steps:

1. The user asks for an image from web server - e.g.: GET https://www.mycompany.test/images/hello.jpg (IP from outside) The rule set notice that the request is from outside and redirect this request to imageproxy with setting quality to 50%: http://localhost:4593/q50/https://www.mycompany.test/images/hello.jpg

2. Imageproxy takes URL from paramater list and request image again: https://www.mycompany.test/images/hello.jpg (from localhost). Now the request is passed to the web server directory.

3. Imageproxy gets image (step 2), converts it and answers the processed image to the user (step 2).

Warning: Rendering the images take some time on the first time of the image access. Thus test the load of your system before going live.