Restart Upstart Instances on System Reboot

A single Upstart job can have multiple instances running:

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$ sudo start my-job port=4000
$ sudo start my-job port=4001
$ sudo start my-job port=4002

However, when the operating system reboots, the job with multiple instances will fail to start, due to instance information is not provided to the job. We can fix this problem by adding a for loop in the script section:

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start on (local-filesystems and net-device-up IFACE!=lo)
stop  on shutdown
script
  for i in `seq 4000 4002`
  do
    exec /path/to/my/job
  done
end script

With this Upstart job, we do not need to provide instance information:

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$ sudo start my-job

Therefore, during system restart, the job will initiate automatically.