Class: HotPotato::SupervisorServer

Inherits:
Object
  • Object
show all
Includes:
Core
Defined in:
lib/hot_potato/supervisor_server.rb

Overview

The supervisor is a process that runs on each machine that participates in the cluster. When it starts it does the following:

  1. Read the routes file

  2. Connect to the Redis server and get the appTask process ID table

  3. Acquire the global lock

  4. If a process is needed, fork a new process for AppTask

  5. Release the global lock

  6. Rinse and Repeat

The supervisor also starts the Heartbeat service and logging service as background threads.

The supervisor can be managed from the command line:

$ bin/supervisor [run|start|stop|restart]

If started without any settings, it will default to run.

Constant Summary collapse

MAX_APP_TASKS = 
32
HEARTBEAT_INTERVAL = 
20
PID_FILE = 
"#{APP_PATH}/tmp/supervisor.pid"
LOG_FILE = 
"#{APP_PATH}/logs/supervisor.log"

Constants included from Core

Core::CONFIG_PATH

Instance Method Summary collapse

Methods included from Core

#acquire_lock, #config, #log, #queue_inject, #queue_subscribe, #release_lock, #set_logger, #stat

Constructor Details

#initialize ⇒ SupervisorServer

Returns a new instance of SupervisorServer.



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# File 'lib/hot_potato/supervisor_server.rb', line 33

def initialize
  @options      = load_options
  @options.mode = parse_options 
  trap("INT") { shutdown }
  self.send(@options.mode)
end

Instance Method Details

#has_capacity ⇒ Object

Determines if this host reached the limit of the number of AppTasks it can run



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# File 'lib/hot_potato/supervisor_server.rb', line 169

def has_capacity
  return stat.keys("hotpotato.apptask.#{@options.hostname}.*").count < @options.max_app_tasks
end

#load_options ⇒ Object

Loads the options, mainly from the config.yml file, into an OpenStruct object.



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# File 'lib/hot_potato/supervisor_server.rb', line 204

def load_options
  options = OpenStruct.new
  options.max_app_tasks = MAX_APP_TASKS
  options.group         = ""
  options.mode          = :run
  options.hostname      = Socket.gethostname
  options.running       = true
  
  if config["servers"]
    config["servers"].each do |server|
      if server["hostname"] == options.hostname
        options.max_app_tasks = server["max_app_tasks"] || MAX_APP_TASKS
        options.group         = server["group"]         || ""
        break
      end
    end
  end
  return options
end

#parse_options ⇒ Object 



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# File 'lib/hot_potato/supervisor_server.rb', line 127

def parse_options
  mode = :run
  op = OptionParser.new do |opts|
    opts.banner = "Usage: #{$0} [run|start|stop|restart]"
    opts.on_tail("-h", "--help", "Show this message") do
      puts op
      exit
    end
  end
  begin
    op.parse!
    mode = (ARGV.shift || "run").to_sym
    if ![:start, :stop, :restart, :run].include?(mode)
      puts op
      exit 1
    end
  rescue
    puts op
    exit 1
  end
  return mode
end

#restart ⇒ Object

Restarts the Supervisor



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# File 'lib/hot_potato/supervisor_server.rb', line 121

def restart
  stop
  sleep 2
  start
end

#run ⇒ Object 



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# File 'lib/hot_potato/supervisor_server.rb', line 40

def run
  $0 = "Hot Potato Supervisor"
  log.info "Starting Hot Potato Supervisor #{HotPotato::VERSION}"
  begin
    start_heartbeat_service
    start_log_service
    routes = HotPotato::Route.routes
    while @options.running do       
      if acquire_lock :supervisor
        log.debug "Lock acquired"          
        routes.app_tasks.each do |app_task|
          if app_task.running_instances < app_task.instances && app_task.allow_group(@options.group)
            if has_capacity
              log.info "Starting AppTask [#{classify(app_task.classname)}]"
              pid = fork do
                Process.setsid
                exec "#{APP_PATH}/bin/app_task #{app_task.classname.to_s}"
              end
              Process.detach pid
              sleep 2
            else
              log.warn "Cannot start AppTask [#{app_task.classname}] - Server at Capacity (Increase max_app_tasks)"
            end
          end
        end            
        release_lock :supervisor        
      end
      sleep (5 + rand(5))
    end
  rescue Exception
    log.error $!
    log.error $@
    exit 1
  end
end

#shutdown ⇒ Object

Kills any running AppTasks on this machine and removes entries from the process table cache. Removes entry for the supervisor in the process table cache.



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# File 'lib/hot_potato/supervisor_server.rb', line 153

def shutdown
  @options.running = false      
  stat.keys("hotpotato.apptask.#{@options.hostname}.*").each do |app_task_key|
    app_task = JSON.parse(stat.get(app_task_key))
    log.info "Killing PID #{app_task.pid} [#{app_task.classname}]"
    Process.kill("INT", app_task.pid) if Process.alive?(app_task.pid)
    stat.del app_task_key
  end
  stat.keys("hotpotato.supervisor.#{@options.hostname}.*").each do |supervisor_key|
    stat.del supervisor_key
  end
  log.info "Stopping Supervisor..."
end

#start ⇒ Object 



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# File 'lib/hot_potato/supervisor_server.rb', line 76

def start
  # Check if we are running
  if File.exists?(PID_FILE)
     pid = 0;
     File.open(PID_FILE, 'r') do |f|
        pid = f.read.to_i
     end
     # Check if we are REALLY running
     if Process.alive?(pid)
       log.fatal "Supervisor is already running on this machine.  Only one instance can run per machine."
       exit 1
     else
       log.info "Supervisor is not running despite the presence of the pid file.  I will overwrite the pid file and start the supervisor."
     end
  end
  Process.daemon
  File.open(PID_FILE, 'w') do |f|
    f.write "#{Process.pid}\n"
  end    
  STDIN.reopen '/dev/null'
  STDOUT.reopen LOG_FILE, 'a'
  STDERR.reopen STDOUT
  STDOUT.sync = true
  STDERR.sync = true
  run
end

#start_heartbeat_service ⇒ Object

Starts a background thread to update the process list in redis.



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# File 'lib/hot_potato/supervisor_server.rb', line 188

def start_heartbeat_service
  si = SupervisorInfo.new
  stat.set si.key, si.to_json
  stat.expire si.key, 120

  Thread.new do
    log.info "Thread created for Supervisor [Heartbeat]"
    loop do
      si.touch
      stat.set si.key, si.to_json, 120
      sleep HEARTBEAT_INTERVAL
    end
  end
end

#start_log_service ⇒ Object

OK, this is not really a log service, but it is responsible for subscribing to the log messages from the AppTasks on this server.



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# File 'lib/hot_potato/supervisor_server.rb', line 175

def start_log_service
  Thread.new do
    log.info "Thread created for Supervisor [Log]"
    queue_subscribe("hotpotato.log.#{@options.hostname}") do |m|
      log_entry = JSON.parse(m)
      if log.respond_to?(log_entry["severity"].to_sym)
        log.send(log_entry["severity"].to_sym, "#{log_entry['classname']} [#{log_entry['pid']}] - #{log_entry['message']}")
      end
    end
  end
end

#stop ⇒ Object

Stops the Supervisor. Requires the existance of a PID file. Calls the shutdown hook to stop AppTasks.



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# File 'lib/hot_potato/supervisor_server.rb', line 105

def stop
  pid = 0
  shutdown      
  if File.exists?(PID_FILE)
    File.open(PID_FILE, 'r') do |f|
      pid = f.read.to_i
    end              
    Process.kill("INT", pid) if Process.alive?(pid)
    File.delete(PID_FILE)
  else
    log.fatal "Supervisor PID file does not exist."
    exit 1
  end
end