Bluepill

Bluepill is a simple process monitoring tool written in Ruby.

Installation

It's hosted on gemcutter.org.

sudo gem install bluepill

In order to take advantage of logging with syslog, you also need to setup your syslog to log the local6 facility. Edit the appropriate config file for your syslogger (/etc/syslog.conf for syslog) and add a line for local6:

local6.*          /var/log/bluepill.log

You'll also want to add /var/log/bluepill.log to /etc/logrotate.d/syslog so that it gets rotated.

Lastly, create the /var/bluepill directory for bluepill to store its pid and sock files.

Usage

DSL

Bluepill organizes processes into 3 levels: application -> group -> process. Each process has a few attributes that tell bluepill how to start, stop, and restart it, where to look or put the pid file, what process conditions to monitor and the options for each of those.

The minimum config file looks something like this:

Bluepill.application("app_name") do |app|
  app.process("process_name") do |process|
    process.start_command = "/usr/bin/some_start_command"
    process.pid_file = "/tmp/some_pid_file.pid"
  end
end

Note that since we specified a PID file and start command, bluepill assumes the process will daemonize itself. If we wanted bluepill to daemonize it for us, we can do (note we still need to specify a PID file):

Bluepill.application("app_name") do |app|
  app.process("process_name") do |process|
    process.start_command = "/usr/bin/some_start_command"
    process.pid_file = "/tmp/some_pid_file.pid"
    process.daemonize = true
  end
end

If you don't specify a stop command, a TERM signal will be sent by default. Similarly, the default restart action is to issue stop and then start.

Now if we want to do something more meaningful, like actually monitor the process, we do:

Bluepill.application("app_name") do |app|
  app.process("process_name") do |process|
    process.start_command = "/usr/bin/some_start_command"
    process.pid_file = "/tmp/some_pid_file.pid"

    process.checks :cpu_usage, :every => 10.seconds, :below => 5, :times => 3
  end
end

We added a line that checks every 10 seconds to make sure the cpu usage of this process is below 5 percent; 3 failed checks results in a restart. We can specify a two-element array for the times option to say that it 3 out of 5 failed attempts results in a restart.

To watch memory usage, we just add one more line:

Bluepill.application("app_name") do |app|
  app.process("process_name") do |process|
    process.start_command = "/usr/bin/some_start_command"
    process.pid_file = "/tmp/some_pid_file.pid"

    process.checks :cpu_usage, :every => 10.seconds, :below => 5, :times => 3        
    process.checks :mem_usage, :every => 10.seconds, :below => 100.megabytes, :times => [3,5]
  end
end

We can tell bluepill to give a process some grace time to start/stop/restart before resuming monitoring:

Bluepill.application("app_name") do |app|
  app.process("process_name") do |process|
    process.start_command = "/usr/bin/some_start_command"
    process.pid_file = "/tmp/some_pid_file.pid"
    process.start_grace_time = 3.seconds
    process.stop_grace_time = 5.seconds
    process.restart_grace_time = 8.seconds

    process.checks :cpu_usage, :every => 10.seconds, :below => 5, :times => 3        
    process.checks :mem_usage, :every => 10.seconds, :below => 100.megabytes, :times => [3,5]
  end
end

We can group processes by name:

Bluepill.application("app_name") do |app|
  5.times do |i|
    app.process("process_name_#{i}") do |process|
      process.group = "mongrels"
      process.start_command = "/usr/bin/some_start_command"
      process.pid_file = "/tmp/some_pid_file.pid"
    end
  end
end

If you want to run the process as someone other than root:

Bluepill.application("app_name") do |app|
  app.process("process_name") do |process|
    process.start_command = "/usr/bin/some_start_command"
    process.pid_file = "/tmp/some_pid_file.pid"
    process.uid = "deploy"
    process.gid = "deploy"

    process.checks :cpu_usage, :every => 10.seconds, :below => 5, :times => 3        
    process.checks :mem_usage, :every => 10.seconds, :below => 100.megabytes, :times => [3,5]
  end
end

To check for flapping:

process.checks :flapping, :times => 2, :within => 30.seconds, :retry_in => 7.seconds

And lastly, to monitor child processes:

process.monitor_children do |child_process|
  child_process.checks :cpu_usage, :every => 10, :below => 5, :times => 3
  child_process.checks :mem_usage, :every => 10, :below => 100.megabytes, :times => [3, 5]

  child_process.stop_command = "kill -QUIT {{PID}}"
end

Note {{PID}} will be substituted for the pid of process in both the stop and restart commands.

A Note About Output Redirection

While you can specify shell tricks like the following in the start_command of a process:

Bluepill.application("app_name") do |app|
  app.process("process_name") do |process|
    process.start_command = "cd /tmp/some_dir && SOME_VAR=1 /usr/bin/some_start_command > /tmp/server.log 2>&1"
    process.pid_file = "/tmp/some_pid_file.pid"
  end
end

We recommend that you not do that and instead use the DSL to capture output from your daemons. Like so:

Bluepill.application("app_name") do |app|
  app.process("process_name") do |process|
    process.start_command = "/usr/bin/env SOME_VAR=1 /usr/bin/some_start_command"

    process.working_dir = "/tmp/some_dir"
    process.stdout = process.stderr = "/tmp/server.log"

    process.pid_file = "/tmp/some_pid_file.pid"
  end
end

The main benefit of using the DSL is that Bluepill will be able to monitor the correct process instead of just watching the shell that spawned your actual server.

CLI

To start a bluepill process and load a config:

sudo bluepill load /path/to/production.pill

To act on a process or group:

sudo bluepill <start|stop|restart|unmonitor> <process_or_group_name>

To view process statuses:

sudo bluepill status

To view the log for a process or group:

sudo bluepill log <process_or_group_name>

To quit bluepill:

sudo bluepill quit

Logging

By default, bluepill uses syslog local6 facility as described in the installation section. But if for any reason you don't want to use syslog, you can use a log file. You can do this by setting the :log_file option in the config:

Bluepill.application("app_name", :log_file => "/path/to/bluepill.log") do |app|
  # ...
end

Keep in mind that you still need to set up log rotation (described in the installation section) to keep the log file from growing huge.

Contribute

Code: http://github.com/arya/bluepill
Bugs/Features: http://github.com/arya/bluepill/issues