Ernie

By Tom Preston-Werner (tom@mojombo.com)

Ernie is a BERT-RPC server implementation that uses an Erlang server to accept incoming connections, and then delegates the request to Ruby handlers.

See the full BERT-RPC specification at bert-rpc.org.

Ernie currently supports the following BERT-RPC features:

• call requests
• cast requests

Ernie was developed for GitHub and is currently in production use serving millions of RPC requests every day. The stability and performance have been exemplary.

Installation

You must have Erlang installed before installing Ernie.

$ gem install ernie -s http://gemcutter.org

Running

Usage: ernie [command] [options]
    -h, --handler HANDLER            Handler file
    -p, --port PORT                  Port
    -n, --number NUMBER              Number of handler instances
    -d, --detached                   Run as a daemon
    -P, --pidfile PIDFILE            Location to write pid file.

Commands:
  <none>                Start an Ernie server.
  reload-handlers       Gracefully reload all of the the ruby handlers
                        and use the new code for all subsequent requests.
  stats                 Print a list of connection and handler statistics.

Examples:
  ernie -d -p 9999 -n 10 -h calc.rb
    Start the ernie server in the background on port 9999 with ten
    handlers, using the calc.rb handler file.

  ernie reload-handlers -p 9999
    Reload the handlers for the ernie server currently running on
    port 9999.

Example Handler

Using a Ruby module and Ernie.expose:

require 'ernie'

module Calc
  def add(a, b)
    a + b
  end
end

Ernie.expose(:calc, Calc)

Using the DSL (this will be deprecated in a future release):

require 'ernie'

mod(:calc) do
  fun(:add) do |a, b|
    a + b
  end
end

Logging

You can have logging sent to a file by adding these lines to your handler:

logfile('/var/log/ernie.log')
loglevel(Logger::INFO)

This will log startup info, requests, and error messages to the log. Choosing Logger::DEBUG will include the response (be careful, doing this can generate very large log files).

Autostart

Normally Ernie handlers will become active after the file has been loaded in. you can disable this behavior by setting:

Ernie.auto_start = false

Example BERT-RPC call for above example

-> {call, calc, add, [1, 2]}

<- {reply, 3}

Using the BERTRPC gem to make calls to Ernie

You can make BERT-RPC calls from Ruby with the BERTRPC gem:

require 'bertrpc'

svc = BERTRPC::Service.new('localhost', 8000)
svc.call.calc.add(1, 2)
# => 3

Known Issues

• Streaming does not work with erlang from debian lenny, but works with erlang-nox package from testing: 1:13.b.2.1-dfsg-1 version works fine. See this message for more details.

Contribute

If you'd like to hack on Ernie, start by forking my repo on GitHub:

http://github.com/mojombo/ernie

To get all of the dependencies, install the gem first. To run ernie from source, you must first build the Erlang code:

rake ebuild

The best way to get your changes merged back into core is as follows:

1. Clone down your fork
2. Create a topic branch to contain your change
3. Hack away
4. Add tests and make sure everything still passes by running rake
5. If you are adding new functionality, document it in the README.md
6. Do not change the version number, I will do that on my end
7. If necessary, rebase your commits into logical chunks, without errors
8. Push the branch up to GitHub
9. Send me (mojombo) a pull request for your branch

Copyright

Copyright (c) 2009 Tom Preston-Werner. See LICENSE for details.