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https://github.com/zimbatm/socketmaster

Zero downtime restarts for your apps
https://github.com/zimbatm/socketmaster

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Zero downtime restarts for your apps

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README 

        
socketmaster(1) -- Zero downtime restart for your apps

======================================================



## SYNOPSIS



`socketmaster` [-listen=URI] [-command=PATH] [-start=MILLIS] [-syslog]



## DESCRIPTION



socketmaster is a generic solution to the restart problem: you want to restart

your app but neither lose any active connection nor refuse new connections.



socketmaster opens the socket you want to listen on and passes it onto your

program. Because socketmaster is simple enough it doesn't need to be restarted

and can keep your file-descriptor indefinitely open.



  * `-command`=PATH:

    Defines the location of the program to execute and pass the file-descriptor

    onto. If you need to add arguments to the program, use -- before the command specific

    arguments or use a wrapper script.



    e.g.

    socketmaster -command  -- -arg1 -arg2



  * `-listen`=URI:

    One of the following schemes are accepted: tcp, tcp4, tcp6 and unix.

    Example: tcp4://localhost:8945 or unix:///tmp/myapp.sock



  * `-start`=MILLIS:

    Determines how long socketmaster waits before signaling the old process.

    If MILLIS is set to zero that feature is disabled.



  * `-syslog`:

    Tells socketmaster to log to syslog.



  * `-user`=LOGIN:

    Sets the child process's uid/gid to the given user (looked up in /etc/passwd).

    This command only works when socketmaster is run as root.



## HOW IT WORKS



On start:



 * socketmaster open the -listen port

 * socketmaster starts the -command with the socket on fd 3 and EINHORN_FDS=3

 * as soon as all child processes are gone, socketmaster stops as well



On SIGUSR1:



 * socketmaster restarts itself with the same command line options

    * without dropping or refusing any connections



On SIGHUP:



 * socketmaster starts a new -command

 * waits for -start milliseconds

 * sends a SIGTERM to the other child processes



Your server is responsible for:



 * opening the socket passed on fd 3

 * not crashing

 * gracefully shutdown on SIGTERM (close the listener, wait for the child

   connections to close)



## ENVIRONMENT



  * `EINHORN_FDS`:

    This variable is set by socketmaster and passed onto the children. Its

    value is always 3 and meant for einhorn compatibility.



## SIGNALS



On SIGHUP, socketmaster starts a new child process, waits for -start and sends a

HUP to the old process.



SIGINT, SIGTERM and SIGQUIT are forwarded to the child processes.



## RELATED PROJECTS



  * [crank](https://github.com/pusher/crank) is the child of socketmaster. It

    supports controlled rolling restarts and dynamic config.

  * [einhorn](https://github.com/stripe/einhorn) is a project with the same goals,

    a wider feature-set and written in ruby.

  * [libancillary](http://www.normalesup.org/~george/comp/libancillary/)

  is a cross-platform C library to work with file-descriptors.

  * [portlisten](http://www.mail-archive.com/[email protected]/msg00002.html)

  another approach to port sharing trough UNIX sockets.

  * [systemd](http://freedesktop.org/wiki/Software/systemd/) is an init system / process manager who supports socket activation and delegation.

  * [circus](http://circus.readthedocs.org/en/latest/) is a process manager with socket delegation.

  * [upstart](http://upstart.ubuntu.com/) is an init system / process manager. See http://manpages.ubuntu.com/manpages/precise/en/man7/socket-event.7.html



## BUGS & CODE



Bug reports and other contributions are welcome!

The project's source and issue tracker is located at



## COPYRIGHT



socketmaster is Copyright (C) 2012 PandaStream 



Permission is hereby granted, free of charge, to any person obtaining a

copy of this software and associated documentation files (the

“Software”), to deal in the Software without restriction, including

without limitation the rights to use, copy, modify, merge, publish,

distribute, sublicense, and/or sell copies of the Software, and to

permit persons to whom the Software is furnished to do so, subject to

the following conditions:



The above copyright notice and this permission notice shall be included

in all copies or substantial portions of the Software.



THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS

OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF

MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.

IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY

CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,

TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE

SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.