python分布式事务方案（一）tcc

python分布式事务方案（一）tcc

随着单体应用的拆分以及服务化的流行，现在分布式事务已经比较常见，分布式事务理论ACID、CAP、BASE等我就不说了，现在就直接说一下一种常见的解决方案-tcc
TCC 其实就是采用的补偿机制，其核心思想是：针对每个操作，都要注册一个与其对应的确认和补偿（撤销）操作。它分为三个阶段：

• Try 阶段主要是对业务系统做检测及资源预留
• Confirm 阶段主要是对业务系统做确认提交，Try阶段执行成功并开始执行 Confirm阶段时，默认 Confirm阶段是不会出错的。即：只要Try成功，Confirm一定成功。
• Cancel 阶段主要是在业务执行错误，需要回滚的状态下执行的业务取消，预留资源释放。

优点： 跟和两阶段提交比起来，实现以及流程相对简单了一些，但数据的一致性比2PC也要差一些

缺点： 缺点还是比较明显的，在2,3步中都有可能失败。TCC属于应用层的一种补偿方式，所以需要程序员在实现的时候多写很多补偿的代码，在一些场景中，一些业务流程可能用TCC不太好定义及处理。

下面介绍下我们应用的一种场景，有一个运维系统需要运用到zabbix，而运维系统拆分出了一个配置中心，下面是子系统依赖图

在配置告警策略时需要调用zabbix接口

这时就涉及到一个分布式事务。由于我们这里只涉及到两个事务，所以我这里就写了一个zabbix代理client，来作为事务协调器

class ZabbixClientProxy(object):
    '''
    zabbix client simple proxy
    '''
    client = models.get_zbx_client()

    def __init__(self):
        self.create_triggers = list()
        self.update_triggers = list()
        self.delete_triggers = list()
        self.update_macros = list()

    def trigger_create(self, name, expression,uuid):
        try:
            trigger = self.client.hosts.trigger_create(name, expression, 1)
            trigger["uuid"]=uuid
            self.create_triggers.append(trigger)
            logger.debug("trigger_create " + name)
            return trigger
        except Exception, e:
            logger.error("trigger_create fail,cause by " + e.message)
            raise

    def trigger_update(self, triggerid, name, expression,uuid):
        try:
            logger.debug("trigger_update " + name)
            old_trigger = self.client.hosts.trigger_get(triggerid)
            update_result = self.client.hosts.trigger_update(
                    triggerid, name=name, expression=expression, priority=1, enable=True)
            old_trigger["uuid"]=uuid
            logger.debug(old_trigger)
            self.update_triggers.append(old_trigger)
            return update_result
        except Exception, e:
            logger.error("trigger_update fail,cause by " + e.message)

    def trigger_delete(self, triggerid,uuid):
        try:
            logger.debug("trigger_delete " + triggerid)
            old_trigger = self.client.hosts.trigger_get(triggerid)
            delete_result = self.client.hosts.trigger_delete(triggerid)
            old_trigger["uuid"]=uuid
            self.delete_triggers.append(old_trigger)
            return delete_result
        except Exception, e:
            logger.error("trigger_delete fail,cause by " + e.message)

    def update_trigger_macro(self, uuid, item_threshold, alert_duration):
        all_hmacros = self.get_macro_by_name(uuid)
        if all_hmacros and len(all_hmacros) > 2:
            self.update_macro(all_hmacros, "DISK_USER_MAX", item_threshold)
            self.update_macro(all_hmacros, "DISK_USER_TIMES", str(alert_duration) + "m")
            self.update_macro(all_hmacros, "DISK_USER_ENABLE", 1)
        else:
            self.create_macro("DISK_USER_MAX", item_threshold, uuid)
            self.create_macro("DISK_USER_TIMES", str(alert_duration) + "m", uuid)
            self.create_macro("DISK_USER_ENABLE", 1, uuid)

    def stop_trigger(self, assets):
        if assets:
            for asset in assets:
                if asset.host is None:
                    continue
                all_hmacros = self.get_macro_by_name(asset.host.uuid)
                if all_hmacros and len(all_hmacros) > 2:
                    self.update_macro(all_hmacros, "DISK_USER_ENABLE", 0)
                else:
                    self.create_macro("DISK_USER_MAX", 80, asset.host.uuid)
                    self.create_macro("DISK_USER_TIMES", "5m", asset.host.uuid)
                    self.create_macro("DISK_USER_ENABLE", 0, asset.host.uuid)

    def get_macro_by_name(self, uuid):
        return self.client.macros.list(uuid)

    def update_macro(self, all_hmacros, macro_name, value):
        for macro in all_hmacros:
            if macro['macro'] == ('{$' + macro_name + '}'):
                try:
                    self.client.macros.update(macro['hostmacroid'], macro=macro_name, value=value)
                    macro['name'] = macro_name
                    self.update_macros.append(macro)
                    logger.debug('update_macro ' + macro_name + ' to ' + str(value))
                except Exception, e:
                    logger.error('update_macro ' + macro_name + ' fail,case by ' + e.message)

    def create_macro(self, macro_name, value, uuid):
        try:
            hostid = self.client.macros._get_hostid(uuid)
            hmacro = self.client.macros.create(macro_name, value, hostid)
            logger.debug("create_macro success,macro_name:" + macro_name + ",value:" + str(value))
        except Exception, e:
            logger.error("create_macro fail,cause by " + e.message)

    def trigger_get(self, triggerid):
        return self.client.hosts.trigger_get(triggerid)

    def trigger_list(self, hostid):
        return self.client.hosts.trigger_list(hostid)

    def item_list(self, uuid):
        return self.client.hosts.item_list(uuid)

    def rollback(self):
        logger.debug("start rollback")
        # rollback create
        for trigger in self.create_triggers:
            try:
                self.client.hosts.trigger_delete(trigger["triggerid"])
                logger.debug('rollback_create_trigger ' + trigger["name"])
            except Exception, e:
                logger.error('rollback_create_trigger ' + trigger["triggerid"] + ' fail,case by ' + str(e.message))
        self.create_triggers = []
        for trigger in self.update_triggers:
            try:
                expression=trigger["expression"].replace(trigger['uuid']+']','{HOST.HOST}]')
                self.client.hosts.trigger_update(trigger["triggerid"], name=trigger["name"],
                                                 expression=expression, priority=1, enable=True)
                logger.debug('rollback_update_trigger ' + trigger["name"])

            except Exception, e:
                logger.error('rollback_update_trigger ' + trigger["triggerid"] + ' fail,case by ' + str(e.message))
        self.update_triggers = []
        for trigger in self.delete_triggers:
            try:
                expression=trigger["expression"].replace(trigger['uuid']+']','{HOST.HOST}]')
                new_trigger = self.client.hosts.trigger_create(trigger["name"], expression, 1)
                logger.debug(new_trigger)
                logger.debug('rollback_delete_trigger ' + trigger["name"])
                # 更新数据中的zabbix trigger id
                alert_models.ConditionTrigger.objects.filter(zabbix_trigger_id=trigger["triggerid"]).update(
                        zabbix_trigger_id=new_trigger["triggerid"])
            except Exception, e:
                logger.error('rollback_delete_trigger ' + trigger["triggerid"] + ' fail,case by ' + str(e.message))
        self.delete_triggers = []

        for macro in self.update_macros:
            try:
                self.client.macros.update(macro['hostmacroid'], macro=macro['name'], value=macro['value'])
            except Exception, e:
                logger.error('rollback_update_macro ' + macro['name'] + ' fail,case by ' + str(e.message))
        logger.debug("end rollback")

事务成功，则提交本地事务，如果失败则调用rollback

def create(self, request, *args, **kwargs):
    '''
    policy add
    '''
    assets = request.data["data"]
    client = ZabbixClientProxy()
    try:
        with transaction.atomic():
            #save policy
            #将client作为参数，对主机、监控项、触发器进行增删改
    except rest_framework_serializers.ValidationError, e:
        logger.exception(e)
        client.rollback()
        raise

这样做还有一个问题就是，在回滚中如果网络突然断了这时会回滚失败，这里我们记录了日志，后面我们会通过扫描日志来做到最终一致性，这里我们后面坐了补偿，下一次修改时会自动修正回滚失败问题。