|Stable release||4.0.33 / December 21, 2012|
|Written in||Java and C|
|License||GNU General Public License|
Resin is a web server and Java application server from Caucho Technology. Resin is provided in two versions, Resin Professional and Resin Open Source (GPL). Resin supports the Java EE standard as well as a mod_php/PHP like engine called Quercus.
Resin Open Source is a open source version of the open core Resin Professional version that Caucho describes as "suitable for hobbyists, developers, and low traffic websites that do not need the performance and reliability enhancements of Resin Professional."
There is some debate on whether or not Resin Open Source is crippleware or open core. March 2013, Techempower, independently picked Resin Open Source as the fastest open source application server, and then used Resin Open Source to compare Java web framework speed against non-Java web framework speed. Resin Open Source dominated the first five positions of every test. Being the best of breed implementation open source solution given a large open source competition would indicate that Resin is not in fact crippled, and is in fact an open core implementation, which implies what is released is useable, but additional features come with the non-open source version. Open core means an open source version of the proprietary version has been made available, and licensed in a manner that donates it to the software community at large for partial or complete re-use.
Resin Open Source lacks optimizations such as built-in caching and features such as clustering support, advanced administration, and the health system that includes HTTP session replication, Java Monitoring, distributed cache replication, and JMS queue replication. Many of these same features are lacking from Apache Tomcat, and Apache Tomcat is not deemed crippleware. While Caucho describes these as "features and enhancements commonly needed in a production environment", Resin Open Source is used without these features.
Within the "resin-admin" web-based management interface of Resin Open Source the majority of menu options return the message "This feature requires Resin Professional and a valid license. Please download Resin Professional and request a free evaluation license." when chosen. Setting many configuration file options and accessing many API methods do not work and generate log error messages to the same effect. Yet Resin Open Source was still useable enough to beat Apache httpd at serving files  and independently picked by Techmepower to represent all Java web frameworks, and ran all of the most popular Java web frameworks on top of Resin Open Source due to its speed, including, Spring, Grails, JRuby, Wicket, and Tapestry, which showed that Java still has the highest overall throughput for web application development.
Resin market share might be small in the grand scheme of Java Application Servers, but many high traffic sites use Resin, including Toronto Stock Exchange, SalesForce.com, Condé Nast (parent company of Vogue, GQ), CNET. NetCraft's February 2012 Survey states Resin grew to 4,700,000 sites and Resin is used on a number of the Million Busiest Sites. Resin was the only Java-based web server mentioned in NetCraft's survey.
Caucho claims that Resin Pro and Resin Open Source is faster than Apache httpd (v 2.4), and therefore focuses on competing with nginx web server. Caucho claims Resin to have comparable speeds to nginx, and that this is one of the reasons for Resin's strong growth. Caucho now claims that Resin Pro is faster than NginX.
Although a Java based server, key pieces of Resin's core networking are written in highly optimized C. Caucho claims Java is the layer that allows Resin to be "full featured" while C provides the speed.
Resin, which was released in 1999, predates Apache Tomcat, and is one of the oldest application servers and web servers.
Product features 
- Elastic Clustering / Cloud support
- 3rd generation clustering optimized for Virtualization 2.0, EC2 and OpenStack deployments
- Session Replication
- Load balancing
- Distributed Cache
- Class compilation
- JIT Profiling and heap analysis
- No GUI required
- JUnit support
- Web Admin
- DevOps support via CLI and REST control of Resin
- Apache Ant/Maven/Ivy integration
- IDE integration
- Flexible project management
- Server Monitoring
- Deployment / Cloud deployment
- Versioned deployment
- Merge paths
- Troubleshooting aids
- Server health reports, baselining and post mortem reporting
- Java EE Web Profile certified,
- Java CDI
- standard Java dependency injection similar to Guice and Spring, part of Java EE
- Transaction support
- Static files/JSP/Servlet/JSF
- Extensible access logging
- URL rewriting
- Proxy caching (similar to Squid)
- Gzip compression
- Virtual Hosts
- Comet/Server push
- mod-php like support via Quercus
Quercus is a Java-based implementation of the PHP language that is included with Resin. According to a slideshow presented by Emil Ong (from Caucho), to a San Francisco Java Meetup Group in April 2008 pertaining to Resin 3.1, an essential difference in the operation of Quercus between the Resin Open Source and the Resin Professional editions is that in Resin Professional the PHP is compiled to Java bytecode whereas in the open source version PHP is executed by an interpreter.
Early versions of the Resin Open Source product were released with problematic licensing but more recent versions are available under a conventional open source license.
Early licensing 
The software license under which Resin was initially released deviated significantly from the conventional definition of open source software. Initially Resin was non-redistributable, and the copyright of any improvements made to the code of the application, if communicated to others, became the property of Caucho Technology. Furthermore, the license stipulated that if any legal action arose out of breach of the licensing terms and a court decision was granted in favor of Caucho Technology all of Caucho's legal expenses must be paid by the licensee. Hence even firms and individuals simply using the software may have been exposed to substantial risk had Caucho found them in breach of any term of the license.
Previous licensing terms for the product included the following, which may have introduced something like a copyleft legal status into the products and services offered by earlier users of Resin:
|“||See the license has the full details. If you distribute a product based on or linked to any Resin code, you must either contact us for a distribution license or satisfy the following:
—Support FAQ, section "Who must purchase a license", circa 2000
As long as you used standard JSP or Java Servlet APIs you did not have any issues.
Current licensing 
Since version 3.0.9, Resin Open Source has been licensed under the GPL License (version 2 or later), a license which has passed through the Open Source Initiative's License Review Process. Consequently current versions of Resin are significantly less hazardous to use or incorporate into software systems than were previous versions.
See also 
- "Caucho Resin is Officially Certified Against the Java EE 6 Web Profile". Infoq.com. Retrieved 2012-10-25.
- "PHP on Java: Best of Both Worlds?". Infoq.com. Retrieved 2012-10-25.
- "Features - Resin and Resin Professional". Archived from the original on 2012-02-27. Retrieved 2012-02-27.
- "Techempower Framework Benchmarks". Techempower.com. Retrieved 2012-10-25.
- "Caucho Resin | Java Application Server | Web Server | Java EE Certified | PaaS/Cloud Ready » resin pro". Caucho.com. Retrieved 2012-10-25.
- "Apache httpd 2.4 versus Resin Pro and Resin Open Source 4.0.31". Caucho.com. Retrieved 2012-04-01.
- PRWeb – Wed, Feb 22, 2012 (2012-02-22). "Caucho's Resin Web Server Powers Over 4.7 Million Sites - Yahoo! News". News.yahoo.com. Retrieved 2012-10-25.
- "February 2012 Web Server Survey | Netcraft". News.netcraft.com. 2012-02-07. Retrieved 2012-10-25.
- "Caucho's Resin Application Server Grew by a Factor of Almost Ten Last Year According to Netcraft". Infoq.com. Retrieved 2012-10-25.
- "NginX 1.2.0 versus Resin 4.0.29 performance tests". Caucho.com. Retrieved 2012-04-01.
- "About Caucho". Caucho.com. Retrieved 2012-04-01.
- "Paul Cowan Discusses the Resin Application Server and Cloud". Infoq.com. Retrieved 2012-10-25.
- "Caucho: Resin Cloud Support: 3rd generation Clustering For Elastic Cloud Scaling". s3.amazonaws.com. Retrieved 2012-10-25.
- "Resin Can Now Act As a Drop-in Replacement for Memcached Solution". Infoq.com. Retrieved 2012-10-25.
- "Caucho Technology » Blog Archive » Resin Pro Health System now and in the future". Blog.caucho.com. 2011-08-26. Retrieved 2012-10-25.
- "Caucho Resin | Java Application Server | Java EE | PaaS Ready » Java EE Web Profile and beyond". Caucho.com. Retrieved 2012-10-25.
- "Caucho Resin | Java Application Server | Java EE | PaaS Ready » Java CDI | Candi". Caucho.com. Retrieved 2012-10-25.
- "Caucho Resin | Java Application Server | Web Server | Java EE Certified | PaaS/Cloud Ready » Resin Web Server". Caucho.com. 2012-02-07. Retrieved 2012-10-25.
- Emil Ong (2008-04-09), Getting Started With Quercus, Caucho Technology, retrieved 2009-08-19 (accompanying Caucho blog entry,additional copy of PDF)
- "Powered by Google Docs". Docs.google.com. Retrieved 2012-10-25.
- New Monthly Caucho Newsletter, Caucho Technology, 2008-02-26, retrieved 2013-02-27, "I think we’re finally getting to the point where we mimic the other implementation of PHP quite precisely (except we have distributed sessions, are faster in compiled mode, etc. :-))."
- Caucho Developer Source License, Version 1.2, Caucho Technology, retrieved 2009-01-30
- Christopher Stacy (2000-04-21). "Re: Resin vs Tomcat". org.apache.tomcat.users. Web link. Retrieved 2009-01-30., archived by WebCite here 
- Resin GPL'ed, retrieved 2009-06-29
- Licenses approved through the OSI License Review Process by name, Open Source Initiative, retrieved 2009-07-28
- Resin Features
- Resin Benchmarks
- Resin: The Instant Application Server
- Force.com uses Resin
- Quote from Dave Moellenhoff, CTO of Salesforce.com about Resin being used for their CRM