Lackr is Fotonauts high speed front-side HTTP proxy server.

ESI on Steroids

ESI, or Edge-Side Include, allows to mix, at request time, markup text and/or data from one or more backends HTTP server. This is a way to build hybrid stacks and support real-life scenarios ranging from

• stack optimisation "Let's get this bit of the page faster by moving its computation from a slow backend technology to a faster one, and leave the rest of the page alone"
• progressive migration "Let's migrate the top bar to the new stack, and keep the rest where it is for now"
• differentiated caching "Let's cache the whole page without the top level corner where we will have either a small login form or user info"
• etc.

Its main features are:

• extended (and extensible) ESI support,
• Handlebars evaluation support,
• being fast and scalable.

It is distributed as a library, and principally meant to be integrated in a jetty 9.0.x server.

Introduction

Lackr is meant to build reverse proxies, something you will setup on your server stack, between the internet and one ore more "backends" servers.

                      Internet
                         |
                         v
               +--------------------+
               | Lackr-based proxy  |
               +--------------------+
                    /         \
                   /           \
                  v             v
   +--------------------+ +--------------------+
   |      Backend 1     | |      Backend 2     |
   +--------------------+ +--------------------+

ESI

If a backend emits something like that:

I'm some text at the top of the main document before an ESI call.
<!--# include virtual="/ex2-shared-esi.html" -->
I'm some text at the bottom of the main document after an ESI call.

Lackr will send one more query to the backend(s) to resolve the placeholder and substitute the content.

Handlebars

Handlebars is a lightweight template engine available in many languages (Java, Javascript, Ruby). We've also developed an Objective-C for Mac and iOS applications.

So if the backend sends something like that:

<!-- lackr:handlebars:template name="template_name" -->
    some text from the template name:{{name}} value:{{value}}
<!-- /lackr:handlebars:template -->
<!-- lackr:handlebars:eval name="template_name" -->
    { "name": "the name", "value": "the value" }
<!-- /lackr:handlebars:eval -->

Lackr will compile the template (in the first pair of lackr tags), and evalutates it against the JSON data in the "eval" tag:

    some text from the template name:the name value:the value

In details

• Getting Started will demonstrate how to start a dummy Lackr server with ESI and Handlebars support
• History explains why we did all this, and maybe why you could be interested.

In excruciating details

• Embed provides hints about Lackr internal architecture, and how to embed Lackr
• Backends example use cases of the composable Backends
• Interpolr how Interpolr can be extended
• Handlebars support Plugin handlebars "helpers"
• Servlet embed as a Servlet

Credits

From Fotonauts:

• Mathieu Poumeyrol (http://github.com/kali)

Copyright (c) 2011-2014 Fotonauts released under the ASF license.