falsk注册etcd

部署web服务集群时，我们希望能动态调整集群大小。当一个新的节点启动时，可以将自己的信息注册给master, 让master把它加入到集群里, 关闭之后也可以把自己从集群中删除。我这里使用的是flask + etcd + confd +nginx来实现。如，新增一个flask节点时，将当前的启动的ip和端口，写到etcd中，设置超时时间如20秒，每隔一段时间如15秒刷新下etcd中的可以。confd从etcd中获取信息，生成nginx的配置文件，重载nginx来扩展或删除新的节点。

1、flask启动后台定时线程来注册etcd

如何在flask中启动后台线程可以参考这里：http://stackoverflow.com/questions/14384739/how-can-i-add-a-background-thread-to-flask

POOL_TIME = 15 #Seconds

# lock to control access to variable
dataLock = threading.Lock()
# thread handler
etcdThread = threading.Thread()
#etcd node
node = None


def create_app(flask_name, service_name, service_port):
    app = Flask(flask_name)

    def interrupt():
        global etcdThread
        etcdThread.cancel()

    def refreshEtcd():
        global etcdThread, node
        with dataLock:
            refresh_etcd(node)
        etcdThread = threading.Timer(POOL_TIME, refreshEtcd, ())
        etcdThread.start()

    def registerEtcd():
        # Do initialisation stuff here
        global etcdThread, node
        with dataLock:
            node register_etcd(service_name, service_port)
        # 定时刷新etcd
        etcdThread = threading.Timer(POOL_TIME, refreshEtcd, ())
        etcdThread.start()

    # 注册
    registerEtcd()  
    atexit.register(interrupt)
    return app

2、python中注册etcd

etcd的python客户端用的是python-etcd，项目地址https://github.com/jplana/python-etcd，目前仅支持etcd v2。

相关代目如下

client = None
def register_etcd(service_name, port):
    import etcd
    global client
    etcd_ip, etcd_port = getConfig('etcd', 'client').split(':')
    client = etcd.Client(host=etcd_ip, port=int(etcd_port))

    host_name = socket.gethostname()
    node_name = '/api/%s/upstream/%s' % (service_name, host_name.replace('-', '_').lower())
    client.write(node_name, '%s:%s' % (host_name, port), ttl=20) #超时时间20秒
    return node_name

def refresh_etcd(node_name):
    client.refresh(node_name, ttl=20)