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Test and Restart Memcached Server

Author:
Digitalxero
Posted:
October 23, 2008
Language:
Python
Version:
1.0
Tags:
middleware cache memcached
Score:
3 (after 3 ratings)

Request-phase cache middleware that checks to make sure the Cache server is running. Starting it if it is not. This is run for every request, it checks to see if it can get a defined item out of the cache, if that fails it tries to set it. Failing that it decides the server is probably crashed, so goes though and attempts to connect to the server. Failing a connection it will launch a new server.

This is probably not useful on large scale multi server deployments as they likely have their own testing for when services crash, but I am using it in a shared hosting environment where I have to run my own copy of memcache manually and cannot setup proper services testing, so I use this to just make sure the cache server is still running.

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import socket
import subprocess

from django.conf import settings
from django.core.cache import cache

class CheckCacheServer(object):
    """
    Request-phase cache middleware that checks to make sure the Cache server is running.
    Starting it if it is not

    Must be first in the middleware stack so it can check before anything else runs
    """
    def __init__(self):
        self.cache_backend = settings.CACHE_BACKEND
        self.servers = self.cache_backend[self.cache_backend.index('//')+2 : self.cache_backend.rindex('/')].split(';')

    def process_request(self, request):
        """
            This is run for every request, it checks to see if it can get a
            defined item out of the cache, if that fails it tries to set it
            Failing that it decides the server is probably crashed, but
            goes though and attempts to connect to the server. Failing a connection
            It will launch a new server.
        """
        if not self.cache_backend.startswith('memcached'):
            return None
            
        alive = cache.get("test-connection")
        if not alive and not cache.set("test-connection", 1, 604800):        
            try:
                memcached = settings.CACHE_SERVER_STRING
            except AttributeError:
                memcached = "memcached -l %s -p %d -c 10 -d"
                
            for server in self.servers:
                ip, port = server.split(':')
                s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
                
                try:
                    s.connect((ip, int(port)))
                except socket.error, e:
                    # not running, start it
                    subprocess.Popen(memcached % (ip, int(port)), shell=True)
                finally:
                    s.close()
        
        return None

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