raindrops - real-time stats for preforking Rack servers

Raindrops is a real-time stats toolkit to show statistics for Rack HTTP servers. It is designed for preforking servers such as Rainbows! and Unicorn, but should support any Rack HTTP server under Ruby 2.0, 1.9, 1.8 and Rubinius on platforms supporting POSIX shared memory. It may also be used as a generic scoreboard for sharing atomic counters across multiple processes.


  • counters are shared across all forked children and lock-free

  • counters are kept on separate cache lines to reduce contention under SMP

  • may expose server statistics as a Rack Middleware endpoint (default: “/_raindrops”)

  • middleware displays the number of actively processing and writing clients from a single request regardless of which worker process it hits.

Linux-only Extra Features!

  • Middleware response includes extra stats for bound TCP and Unix domain sockets (configurable, it can include stats from other TCP or UNIX domain socket servers).

  • TCP socket stats use efficient inet_diag facilities via netlink instead of parsing /proc/net/tcp to minimize overhead. This was fun to discover and write.

  • TCP_Info reporting may be used to check stat for every accepted client on TCP servers

Users of older Linux kernels need to ensure that the the “inet_diag” and “tcp_diag” kernel modules are loaded as they do not autoload correctly


We recommend GCC 4+ (or compatible) to support the atomic builtins (_syncadd,sub}_and_fetch()). For non-GCC 4+ users, we also support compilation with the {libatomic_ops package starting with Raindrops 0.4.0.

If you're using a packaged Ruby distribution, make sure you have a C compiler and the matching Ruby development libraries and headers.

If you use RubyGems:

gem install raindrops

Otherwise grab the latest tarball from:


Unpack it, and run “ruby setup.rb”


See Raindrops::Middleware and Raindrops::LastDataRecv documentation for use Rack servers. The entire library is fully-documented and we are responsive on the mailing list (raindrops@librelist.org) if you have any questions or comments.


You can get the latest source via git from the following locations:

git://repo.or.cz/raindrops.git (mirror)

You may browse the code from the web and download the latest snapshot tarballs here:

Inline patches (from “git format-patch”) to the mailing list are preferred because they allow code review and comments in the reply to the patch.

We will adhere to mostly the same conventions for patch submissions as git itself. See the Documentation/SubmittingPatches document distributed with git on on patch submission guidelines to follow. Just don't email the git mailing list or maintainer with raindrops patches.

raindrops is currently dual-licensed under the LGPLv2.1 and LGPLv3. To allow for a transition to future versions of the LGPL, contributors are required to sign-off changes allowing allowing the project leader to relicense raindrops under newer versions of the LGPL (which should be similar in spirit to the existing LGPL).


All feedback (bug reports, user/development discussion, patches, pull requests) go to the mailing list: raindrops@librelist.org

The mailing list is mirrored to Gmane, all information about the group is here:


Mailing list archives in mbox format may be downloaded here: