Webimages across web servers:

Landisc now has the capability of using a 'passthrough proxy' for passing images from a hidden private intranet web server through a public web server to an internet user.

Why is this important? All public web servers are not windows computers. All public web servers will not allow Landisc to be located on it.

NOTE: When the Web Server needs to access the Landisc database on another server, the user that is executing the web server software MUST BE A DOMAIN USER! The default user that executes the web server software is always the LOCAL_SERVICE user.

Case in point:

A jurisdiction that uses an IBM mainframe/minicomputer that, of course, does not run windows as an operating system. And, of course, cannot execute windows applications.


A public web server needs to allow a passthrough proxy to a private web server (that uses windows for an operating system) to execute a cgi application (i.e. webimage.dbw). In this case, the private web server will actually execute webimage and stream the image to the internet user through the public web server.

Is this a security issue?

No. The private web server is still hidden from the public. The internet user will not even see the private web server, just the result.

An example:

160x120 resized image

When you go to this page on the Landisc public server, within the HTML code is:

<img src="/cgi-bin/webimage.dbw?Project=newtown&ParcelID='B0303037'&Resize=400x300">

Within the configuration of the web server, all cgi-bin requests are sent to the private web server via the proxy instructions. With Apache web server software, the instructions are simply:

ProxyPass /cgi-bin/ http://MyIntranetServer/cgi-bin/
ProxyPassReverse /cgi-bin/ http://MyIntranetServer/cgi-bin/

The MyIntranetServer computer is an intranet web server. Because of the proxy instructions, all "/cgi-bin/" instructions are passed to the private web server, executed, and then returned to the public web server and passed to the internet user. In the example, the NEWTOWN (Project=newtown) database's Parcel B0303037 (ParcelID='B0303037') has an image that is about 50KB. Using the resizer attribute (Resize=400x300), the image is reduced to about 9KB. Keep in mind that some Landisc projects have images that are in excess of 1MB each in size.

The registry on the intranet server will need to be modified to execute the dbw applet as a cgi applet.

This will allow intranet and extranet users to access one Landisc database without compromising security. This will also allow the images to be resized to a smaller image BEFORE it is streamed to the internet user, reducing bandwidth and allows timely responses for the streaming of the images.

This also eliminates having to extract and maintain tens (or even hundreds) of thousands of duplicate images. This also eliminates having a second Landisc database located outside the firewall. Both of those scenarios can be a housekeeping nightmare.

Should this be the method for your website?

Yes! We have clients that extract all the Landisc images and then resize the images TWICE (one as a 160x120 thumb and one that is 400x300). Also, if the webuser wanted to see the image in full screen, the resulting image will be highly distorted when stretched to 800x600 or even 1024x768. This means that for every extracted image they have to maintain 3 images! Talk about a housekeeping nightmare!

WebImaging Flowchart

How fast is the image returned to the internet user?

Bear in mind that the demo site is sharing a 768Kbps upstream bandwidth. This still allows the image to be passed in 1-2 seconds. So for a high speed web site, the response will be even faster. Easily, the response will be an acceptable speed of 1 second or less, when resized. Larger, unresized images, can take longer.

Intranet Stress Test  Internet Stress Test

Does the private web server have to use Apache?

No. IIS can also execute the cgi applications. IIS also has instructions for setting up the proxy passthrough instructions for those that use IIS.

Does the public web server have to use Apache or IIS?

No! IBM 1 or IBM 2 have instructions for setting up the proxy passthrough for the IBM HTTP server.

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