如何用python编写collectd的plugin

collect的python plugin内嵌了一个python的解释器，可以方便我们用python自定义collectd的plugin，各个callback的函数定义可以参考collectd python plugin。比如自定义一个统计cpu利用率的plugin:

cpu_usage_plugin.py

#!/usr/bin/env pythonimport subprocessimport tracebackdef get_cpu_usage():    cmd = "grep 'cpu ' /proc/stat | awk '{usage=($2+$4)*100/($2+$4+$5)} END {print usage}'"    result = run(cmd)    for line in result:        try:            usage = float(line)            return usage        except:            raise Exception("Failed to parse cpu usage")def run(cmd):    try:        result = []        proc = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, close_fds=True)        (stdout, stderr) = proc.communicate()        output = stdout.split("\n")        for line in output:            if line == '':                continue            result.append(line)        return result    except Exception as err:        raise Exception("failed to execute command: %s, reason: %s" % (' '.join(cmd), err.message))class CPUStatMon(object):    def __init__(self):        self.plugin_name = "cpu_stat"        self.interval = 30        self.hostname = None        self.verbose_logging = False    def log_verbose(self, msg):        if not self.verbose_logging:            return        collectd.info('%s plugin [verbose]: %s' % (self.plugin_name, msg))    '''    to store/initialize the internal state like a socket connection    def init(self):        self.SOCKET_CONN = create_sockect_conn()    '''    def configure_callback(self, conf):        for node in conf.children:            val = str(node.values[0])            if node.key == "HostName":                self.hostname = val            elif node.key == 'Interval':                self.interval = int(float(val))            elif node.key == 'Verbose':                self.verbose_logging = val in ['True', 'true']            elif node.key == 'PluginName':                self.plugin_name = val            else:                collectd.warning('[plugin] %s: unknown config key: %s' % (self.plugin_name, node.key))    def dispatch_value(self, plugin, host, type, type_instance, value):        self.log_verbose("Dispatching value plugin=%s, host=%s, type=%s, type_instance=%s, value=%s" %                         (plugin, host, type, type_instance, str(value)))        val = collectd.Values(type=type)        val.plugin = plugin        val.host = host        val.type_instance = type_instance        val.interval = self.interval        val.values = [value]        val.dispatch()        self.log_verbose("Dispatched value plugin=%s, host=%s, type=%s, type_instance=%s, value=%s" %                         (plugin, host, type, type_instance, str(value)))    def read_callback(self):        try:            usage = get_cpu_usage()            type = 'cpu_usage_percent'            type_instance = "used"            value = usage            self.dispatch_value(self.plugin_name, self.hostname, type, type_instance, value)        except Exception as exp:            self.log_verbose(traceback.print_exc())            self.log_verbose("plugin %s run into exception" % (self.plugin_name))            self.log_verbose(exp.message)if __name__ == '__main__':    result = get_cpu_usage()    print resultelse:    import collectd    cpu_status_mon = CPUStatMon()    collectd.register_config(cpu_status_mon.configure_callback)    '''    # register the init function    collectd.register_init(cpu_status_mon.init)    '''    collectd.register_read(cpu_status_mon.read_callback)

collectd.conf中enable python plugin并增加如下配置：

<Plugin python>    ModulePath "/opt/collectd/lib/collectd"    Import "cpu_usage_plugin"    <Module cpu_usage_plugin>        Interval 30        PluginName "cpu_usage"        HostName "demo_host"        Verbose false    </Module></Plugin>

值得注意的是:

• 对于dispatch_value函数中type参数的值，可以直接传入字符串gauge，derived，count等collectd的内建数据类型，也可以在types.db中对这些数据类型做一个map，看起来更有意义，如下所示：

• types.dbcpu_usage_percentage               value:GAUGE:0:U

• 如果想维持某些变量的状态，可以把该通过regiseter_init来注册包含该变量的函数，如代码中被注释掉的地方。
• 如果有多个自定义的python plugin，在<Plugin python></Plugin>片段中使用多个Import导入相应的模块，并定义多个<Module></Module>片段。
• 默认情况下，collectd的log在syslog中。