CLOSER

run, monitor and closer remote SSH processes automatically

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CLOSER

Closer was born because I had trouble with killing up processes I set up remotely via SSH. That is, you want to run some SSH process in the background, and then you want to kill it, just like you would a local subprocess.

I couldn’t find a good solution, so here’s my take on it.

Closer has evolved to do more than just automatic remote process cleanup. Here are the main features:

  • kill the remote process (either by choice, or automatically at the end of the calling process)
  • capture the remote process’s output
  • live monitoring of remote process output
  • get a callback upon remote process’ death

Installation

You must install closer both on your local machine and the remote machine:

$ pip install closer

Caveats

  • Again, closer must be installed on the remote machine for it to work.
  • closer uses TCP communication with the remote process. Firewalls may block closer.

Example Run

In this example we connect via SSH to a machien with IP 10.50.50.11 with a user called vagrant. We run a bash shell that itself runs a sleep, not before echoing whatup to standard output.

After we quit the IPython process, the Remote object kills the remote process for us (becasue we specified cleanup=True.

$ ipython
Python 2.7.12+ (default, Sep 17 2016, 12:08:02) 
Type "copyright", "credits" or "license" for more information.

IPython 5.1.0 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

In [1]: import closer.remote

In [2]: r = closer.remote.Remote( 'vagrant', '10.50.50.11', [ 'bash', '-c', 'echo whatup; sleep 1500;' ] )

In [3]: r.background(cleanup=True) # launches remote process in the background

whatup
In [4]: quit()  # remote process dies automatically - check it out on your own remote server

Explicitly Closing All Remote Background (with cleanup=True) Processes and Handling SIGTERM

closer relies on atexit If your process dies as a result of receiving SIGTERM, the atexit handler will not run.

closer provides a solution by allowing you to explicitly close all Remote processes:

    closer.remote.Remote.tidyUp()

NOTE: tidyUp() will ONLY WORK for Remote objects that run with .background(cleanup=True). If you did not specify cleanup=True it is false by default.

To handle SIGTERM, e.g.:

import closer.remote
import signal
import sys

def handleSIGTERM( * args ):
    closer.remote.Remote.tidyUp()
    sys.exit( 1 )

signal.signal( signal.SIGTERM, handleSIGTERM )

My Remote Machine’s closer Script is Not in the System PATH

use the .setCloserCommand(), e.g.

remoteObject = closer.remote.Remote( ... )
remoteObject.setCloserCommand( '/path/to/closer' )

I want to specify a different SSH port or other options

here you go:

remoteObject.sshPort = SOME_OTHER_PORT
remoteObject.sshOptions( 'StrictHostKeyChecking=no' ) # this goes into the -o ssh flag

Other Perks

The Remote class also allows you to run processes synchronously, i.e. the following IPython session:

In [7]: r = closer.remote.Remote( 'vagrant', '10.50.50.11', [ 'ls', '-ltr', '/var' ] )

In [8]: r.foreground()
total 44
drwxrwsr-x  2 root staff  4096 Apr 10  2014 local
drwxr-xr-x  2 root root   4096 Apr 10  2014 backups
drwxr-xr-x  2 root root   4096 Feb  8 20:41 opt
drwxrwsr-x  2 root mail   4096 Feb  8 20:41 mail
lrwxrwxrwx  1 root root      4 Feb  8 20:41 run -> /run
lrwxrwxrwx  1 root root      9 Feb  8 20:41 lock -> /run/lock
drwxr-xr-x  5 root root   4096 Feb  8 20:42 spool
drwxrwxrwt  2 root root   4096 Feb  8 20:43 crash
drwxr-xr-x 11 root root   4096 Feb  8 21:35 cache
drwxr-xr-x 47 root root   4096 Feb  8 21:36 lib
drwxr-xr-x  3 root root   4096 Feb 12 20:22 chef
drwxrwxrwt  2 root root   4096 Feb 12 22:11 tmp
drwxrwxr-x 10 root syslog 4096 Feb 13 18:49 log

And you can capture the output if you like:

In [6]: r = closer.remote.Remote( 'vagrant', '10.50.50.11', [ 'ls', '-ltr', '/var' ] )

In [7]: text = r.output()

In [8]: text.split('\n')
Out[8]: 
['total 44',
 'drwxrwsr-x  2 root staff  4096 Apr 10  2014 local',
 'drwxr-xr-x  2 root root   4096 Apr 10  2014 backups',
 'drwxr-xr-x  2 root root   4096 Feb  8 20:41 opt',
 'drwxrwsr-x  2 root mail   4096 Feb  8 20:41 mail',
 'lrwxrwxrwx  1 root root      4 Feb  8 20:41 run -> /run',
 'lrwxrwxrwx  1 root root      9 Feb  8 20:41 lock -> /run/lock',
 'drwxr-xr-x  5 root root   4096 Feb  8 20:42 spool',
 'drwxrwxrwt  2 root root   4096 Feb  8 20:43 crash',
 'drwxr-xr-x 11 root root   4096 Feb  8 21:35 cache',
 'drwxr-xr-x 47 root root   4096 Feb  8 21:36 lib',
 'drwxr-xr-x  3 root root   4096 Feb 12 20:22 chef',
 'drwxrwxrwt  2 root root   4096 Feb 12 22:11 tmp',
 'drwxrwxr-x 10 root syslog 4096 Feb 13 18:49 log',
 '']

By default .foreground() will raise an exception if the process fails. You can disable this behaviour with .foreground( check = False ).

Live Monitoring of Remote Process Output and Death

You can monitor a remote processes’ output and death events using the liveMonitor method. Try this:

def onOutput( line ):
    print "got: {}".format( line )

def onProcessEnd( exitCode ):
    print "process died with exitCode={}".format( exitCode )

tested = closer.remote.Remote( 'my-user', 'my-host', "bash -c 'for i in 1 2 3 4 5 6 7 8 9 10; do echo $i; sleep 1; done; exit 7'", shell = True )
tested.liveMonitor( onOutput = onOutput, onProcessEnd = onProcessEnd, cleanup = True )
LET_PROCESS_DIE_NATURALLY = 12
time.sleep( LET_PROCESS_DIE_NATURALLY )

the onOutput callback will be called for every line the remote process produces on its standard output, and the onProcessEnd will be called when the remote process exits.

Python 3

closer works with Python 3 just fine, but there is a caveat. Assuming that the local host has the Python 3 closer installed:

  • if the remote host has a Python 3 based closer - no problem
  • if the remote host has a Python 2 based closer, you must set the closer command like so:
remoteObject.setCloserCommand( '/path/to/closer' ) 

otherwise, it will look for a local closer3 script and will not find one.

PYTHON 2 SUPPORT WILL BE DROPPED EVENTUALLY