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Phusion Passenger 4.0 Release Candidate 2

By Hongli Lai on February 27th, 2013

Phusion Passenger is an Apache and Nginx module for deploying Ruby and Python web applications. It has a strong focus on ease of use, stability and performance. Phusion Passenger is built on top of tried-and-true, battle-hardened Unix technologies, yet at the same time introduces innovations not found in most traditional Unix servers. Since mid-2012, it aims to be the ultimate polyglot application server.

We know many users are eagerly awaiting the final release of Phusion Passenger 4.0. The 4.x series is a huge improvement over the 3.x series: during the development of 4.0, we’ve introduced a myriad of changes which we’ve covered in past beta preview articles:

Today we are proud to announce Release Candidate 2 of Phusion Passenger 4.0. Release Candidate 1 has been skipped because a few bug fixes were applied right after RC 1 was tagged.

Changes in 4.0 RC 1 and RC 2

The focus of RC 1 and RC 2 have been on improving stability and on refining previously introduced features. We’ve closed over 100 issues in our issue tracker. We couldn’t have done this without the fantastic feedback from our users, especially those from many Phusion Passenger Enterprise customers who have beta tested the RC previews in their staging environments.

The changes in RC 1 and RC 2 are as follows:

  • The Nginx version now supports the passenger_app_root configuration option.
  • The Enterprise memory limiting feature has been extended to work with non-Ruby applications as well.
  • Application processes that have been killed are now automatically detected within 5 seconds. Previously Phusion Passenger needed to send a request to the process before detecting that it’s gone. This change means that when you kill a process by sending it a signal, Phusion Passenger will automatically respawn it within 5 seconds (provided that the process limit settings allow respawning).
  • Phusion Passenger Standalone’s HTTP client body limit has been raised from 50 MB to 1 GB.
  • Python 3 support has been added.
  • The build system has been made compatible with JRuby and Ruby 2.0. This does not mean that Phusion Passenger works on Ruby 2.0; please read on for more about this subject.
  • The installers now print a lot more information about detected system settings so that the user can see whether something has been wrongly detected.
  • Some performance optimizations. These involve further extending the zero-copy architecture, and the use of hash table maps instead of binary tree maps.
  • Many potential crasher and freezer bugs have been fixed.
  • Error diagnostics have been further improved.
  • Many documentation improvements.

What about Ruby 2.0?

UPDATE June 6 2013: Phusion Passenger 4.0.0 fully supports Ruby 2.0! See this article for clarification.

We are just as excited about Ruby 2.0 as many of you are. Since 2.0 was released a few days ago, we’ve been testing Phusion Passenger on it. We really wanted to release RC 2 with Ruby 2.0 support, but a few things stood in our way so we had to postpone this goal.

  • We couldn’t get Ruby 2.0.0 installed on OS X Mountain Lion. The compiled Ruby crashes during Ruby 2.0.0’s build process with a low-level error ([BUG] Stack consistency error). Apparently we aren’t the only ones.
  • We were able to get it installed on a Debian VM, but it does not pass all the Phusion Passenger unit tests. It fails on some tests with obscure errors that seem to indicate bugs in Ruby, e.g. errors in which Ruby cannot figure out where the exception came from.

We recommend sticking with 1.9.3 in the mean time until the next Ruby 2.0 patchlevel release.

Release Candidate 2 timeline & download

Phusion Passenger Enterprise customers are given priority access to Release Candidate 2. They can download RC 2 from the Customer Area immediately.

Phusion Passenger Enterprise customers: download RC 2 from Customer Area

The release of the open source version will follow in one week, on March 5 2013. Of course, open source users who want to stay on the bleeding edge are free to obtain the latest sources from the open source Phusion Passenger git repository at any time.

When the open source version is released, users can install it by following the in-depth installation and upgrade instructions in the Installation section of the documentation. The manual also covers installation of beta releases.


We are excited about the final release. You can help us by testing RC 2 and reporting any bugs. Please submit bug reports to our bug tracker.

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