Capistrano 部署 Rails 项目速记中解决了代码更新时候 mongrel/backgroundrb 重启等问题，还需要保证系统重启时服务能够自动启动。
mongrel cluster 自带了 mongrel-cluster 启动管理脚本，Debian 系统的话链接 mongrel_cluster.yml 到 /etc/mongrel-cluster/sites-enabled/ 目录，系统启动的时候 /etc/init.d/mongrel-cluster 会自动启动 mongrel daemon，然而 backgroundrb 的启动问题还是没有解决，需要手工写启动脚本，google 了一番之后，找到 Monit 这个小工具：
# 摘自 monit deb package description.
A utility for monitoring and managing daemons or similar programs
monit is a utility for monitoring and managing daemons or similar
programs running on a Unix system. It will start specified programs
if they are not running and restart programs not responding.
.
monit supports:
* Daemon mode - poll programs at a specified interval
* Monitoring modes - active, passive or manual
* Start, stop and restart of programs
是否可以用 Monit 来启动 mongrel 和 backgroundrb 呢，答案是肯定的，事实上这也应该是推荐方式。
安装 Monit
$sudo aptitude install monit
修改 /etc/default/monit 配置：
startup=1
CHECK_INTERVALS=30 # monit 监控检测时间价格，推荐设置成 30 秒
配置 monit
$sudo grep '^[^#]' /etc/monit/monitrc
set daemon 30
set logfile syslog facility log_daemon
set httpd port 2812 and
use address localhost # only accept connection from localhost
allow localhost # allow localhost to connect to the server and
include /etc/monit/conf.d/*
$sudo mkdir /etc/monit/conf.d
配置 Daemon 项
$cat 001_neo_mongrel.conf
check process mongrel_neo_8000
with pidfile /project/code/path/shared/pids/mongrel.8000.pid
start program = "/usr/bin/mongrel_rails cluster::start -C /project/code/path/current/config/mongrel_cluster.yml --clean --only 8000"
stop program = "/usr/bin/mongrel_rails cluster::stop -C /project/code/path/current/config/mongrel_cluster.yml --only 8000"
if totalmem is greater than 110.0 MB for 4 cycles then restart
if cpu is greater than 80% for 4 cycles then restart
if 20 restarts within 20 cycles then timeout
group neo
check process mongrel_neo_8001
with pidfile /project/code/path/shared/pids/mongrel.8001.pid
start program = "/usr/bin/mongrel_rails cluster::start -C /project/code/path/current/config/mongrel_cluster.yml --clean --only 8001"
stop program = "/usr/bin/mongrel_rails cluster::stop -C /project/code/path/current/config/mongrel_cluster.yml --only 8001"
if totalmem is greater than 110.0 MB for 4 cycles then restart
if cpu is greater than 80% for 4 cycles then restart
if 20 restarts within 20 cycles then timeout
group neo
check process mongrel_neo_8002
with pidfile /project/code/path/shared/pids/mongrel.8002.pid
start program = "/usr/bin/mongrel_rails cluster::start -C /project/code/path/current/config/mongrel_cluster.yml --clean --only 8002"
stop program = "/usr/bin/mongrel_rails cluster::stop -C /project/code/path/current/config/mongrel_cluster.yml --only 8002"
if totalmem is greater than 110.0 MB for 4 cycles then restart
if cpu is greater than 80% for 4 cycles then restart
if 20 restarts within 20 cycles then timeout
group neo
$ cat 003_neo_brb.conf
check process brb_imigu_11006
with pidfile /project/code/path/shared/pids/backgroundrb_11006.pid
start program = "/bin/su -c 'cd /project/code/pathcurrent && RAILS_ENV=production nohup ./script/backgroundrb start > /dev/null 2>&1' josh"
stop program = "/bin/su -c 'cd /home/josh/www/imigu/current && RAILS_ENV=production && ./script/backgroundrb stop' josh"
group neo
启动 Monit 和监测
$sudo /etc/init.d/monit restart
$sudo monit -c /etc/monit/monitrc status #查看系统状态
通过 monit 已经可以自动启动管理 mongrel 和 backgroundrb，那么谁来保证 monit 的稳定运行呢，答案是 linux 系统 init。
编辑 /etc/inittab 加入：
# Run monit in standard run-levels
mo:2345:respawn:/usr/sbin/monit -Ic /etc/monit/monitrc
mo:06:wait:/usr/sbin/monit -Ic /etc/monit/monitrc stop all
重启 monit
$sudo /etc/init.d/monit stop
$sudo telinit q
参考：
- Monit man page
- 2008, Ezra Zygmuntowicz and Bruce Tate, Deploying Rails Applications
