Storm-源码分析- Storm中Zookeeper的使用

在backtype.storm.cluster.clj中, 定义了storm对于Zookeeper的使用

 

ClusterState

首先定义操作Zookeeper集群的interface

(defprotocol ClusterState
  (set-ephemeral-node [this path data])
  (delete-node [this path])
  (create-sequential [this path data])
  (set-data [this path data])  ;; if node does not exist, create persistent with this data 
  (get-data [this path watch?])
  (get-children [this path watch?])
  (mkdirs [this path])
  (close [this])
  (register [this callback])
  (unregister [this id])
  )

实现和生成用于操作Zookeeper集群的record
首先创建zk-client, 并在zk上创建STORM-ZOOKEEPER-ROOT目录
接着定义,
    callbacks, callback集合
    active, 标志zk集群状态
    zk, zk client

创建zk client的时候, 设置了watcher, 即zk server当状态发生变化时会给client发送event, 此处client设置的watcher会调用callbacks来处理server发送的event

Storm在操作Zookeeper时, 使用CuratorFramework(http://curator.incubator.apache.org/curator-framework/index.html)

最后实现ClusterState protocol, 其中register和unregister是用来添加/删除callbacks的, 其他都是些zk的常规操作

(defn mk-distributed-cluster-state [conf]
  (let [zk (zk/mk-client conf (conf STORM-ZOOKEEPER-SERVERS) (conf STORM-ZOOKEEPER-PORT) :auth-conf conf)]
    (zk/mkdirs zk (conf STORM-ZOOKEEPER-ROOT))
    (.close zk))
  (let [callbacks (atom {})
        active (atom true)
        zk (zk/mk-client conf
                         (conf STORM-ZOOKEEPER-SERVERS)
                         (conf STORM-ZOOKEEPER-PORT)
                         :auth-conf conf
                         :root (conf STORM-ZOOKEEPER-ROOT)
                         :watcher (fn [state type path]
                                     (when @active
                                       (when-not (= :connected state)
                                         (log-warn "Received event " state ":" type ":" path " with disconnected Zookeeper."))
                                       (when-not (= :none type)
                                         (doseq [callback (vals @callbacks)]
                                           (callback type path))))
                                       ))]
    (reify
     ClusterState
     (register [this callback]
               (let [id (uuid)]
                 (swap! callbacks assoc id callback)
                 id
                 ))
     (unregister [this id]
                 (swap! callbacks dissoc id))

     (set-ephemeral-node [this path data]
                         (zk/mkdirs zk (parent-path path))
                         (if (zk/exists zk path false)
                           (try-cause
                             (zk/set-data zk path data) ; should verify that it's ephemeral
                             (catch KeeperException$NoNodeException e
                               (log-warn-error e "Ephemeral node disappeared between checking for existing and setting data")
                               (zk/create-node zk path data :ephemeral)
                               ))
                           (zk/create-node zk path data :ephemeral)
                           ))
     
     (create-sequential [this path data]
       (zk/create-node zk path data :sequential))
     
     (set-data [this path data]
               ;; note: this does not turn off any existing watches
               (if (zk/exists zk path false)
                 (zk/set-data zk path data)
                 (do
                   (zk/mkdirs zk (parent-path path))
                   (zk/create-node zk path data :persistent)
                   )))
     
     (delete-node [this path]
                  (zk/delete-recursive zk path)
                  )
     
     (get-data [this path watch?]
               (zk/get-data zk path watch?)
               )
     
     (get-children [this path watch?]
                   (zk/get-children zk path watch?))
     
     (mkdirs [this path]
             (zk/mkdirs zk path))
     
     (close [this]
            (reset! active false)
            (.close zk))
     )))

 

StormClusterState

定义针对Storm定制的zk操作协议, 包含各种storm里面的信息在zk上的读写

(defprotocol StormClusterState
  (assignments [this callback])
  (assignment-info [this storm-id callback])
  (active-storms [this])
  (storm-base [this storm-id callback])

  (get-worker-heartbeat [this storm-id node port])
  (executor-beats [this storm-id executor->node+port])
  (supervisors [this callback])
  (supervisor-info [this supervisor-id])  ;; returns nil if doesn't exist

  (setup-heartbeats! [this storm-id])
  (teardown-heartbeats! [this storm-id])
  (teardown-topology-errors! [this storm-id])
  (heartbeat-storms [this])
  (error-topologies [this])

  (worker-heartbeat! [this storm-id node port info])
  (remove-worker-heartbeat! [this storm-id node port])
  (supervisor-heartbeat! [this supervisor-id info])
  (activate-storm! [this storm-id storm-base])
  (update-storm! [this storm-id new-elems])
  (remove-storm-base! [this storm-id])
  (set-assignment! [this storm-id info])
  (remove-storm! [this storm-id])
  (report-error [this storm-id task-id error])
  (errors [this storm-id task-id])

  (disconnect [this])
  )

首先判断是否第一次mk-storm-cluster-state, 既是否进行过zk cluster state的创建, 如果没有调用mk-distributed-cluster-state
接着, 定义一系列的callbacks, 并调用cluster-state的register, 注册到callbacks列表中
       state-id 就是register返回的callback的uuid
再者, 在zk上创建storm的子目录
最后, 实现StormClusterState协议, 实现各种zk数据的读写

(defn mk-storm-cluster-state [cluster-state-spec]
  (let [[solo? cluster-state] (if (satisfies? ClusterState cluster-state-spec)
                                [false cluster-state-spec]
                                [true (mk-distributed-cluster-state cluster-state-spec)])
        assignment-info-callback (atom {})
        supervisors-callback (atom nil)
        assignments-callback (atom nil) ;在StormClusterState.assignments中被set
        storm-base-callback (atom {})
        state-id (register
                  cluster-state
                  (fn [type path]
                    (let [[subtree & args] (tokenize-path path)] ;将path按'/'分割
                      (condp = subtree ;对path的subtree部分进行swith…case
                          ASSIGNMENTS-ROOT (if (empty? args)
                                             (issue-callback! assignments-callback) ;issue-callback!, 执行并删除该callback, 保证callback只被执行一次
                                             (issue-map-callback! assignment-info-callback (first args)))
                          SUPERVISORS-ROOT (issue-callback! supervisors-callback)
                          STORMS-ROOT (issue-map-callback! storm-base-callback (first args))
                          ;; this should never happen
                          (halt-process! 30 "Unknown callback for subtree " subtree args)
                          )
                      )))]
    (doseq [p [ASSIGNMENTS-SUBTREE STORMS-SUBTREE SUPERVISORS-SUBTREE WORKERBEATS-SUBTREE ERRORS-SUBTREE]]
      (mkdirs cluster-state p))
    (reify
     StormClusterState
     )

 

例子

通过一个场景来说明storm怎样使用zookeeper

supervisor中的mk-synchronize-supervisor, 主要用于下载新的, 并删除不使用的topology代码
所以这个逻辑光执行一次是不够的, 需要当每次assignment发生变化的时候就执行一次

storm是利用zookeeper的watcher来解决这个问题
1. 在mk-distributed-cluster-state中创建zk client的时候配置watcher, 当收到zk server的event的时候, 调用callbacks列表里面的callback进行处理

2. 在mk-storm-cluster-state 中将callback加入cluster-state的callback列表
    而这个callback本身, 就是根据event中的path(代表哪部分数据发生change)来issue在storm-cluster-state中维护的一系列callback
    比如, 当ASSIGNMENTS-ROOT发生变化时, 会调用assignments-callback 
3. 那么也就是说只需要将mk-synchronize-supervisor, set到assignments-callback, 就可以保证当ASSIGNMENTS-ROOT发生变化时, 调用mk-synchronize-supervisor去同步topology代码
   什么时候set? 在第一次调用mk-synchronize-supervisor的时候

sync-callback (fn [& ignored] (.add event-manager this))
assignments-snapshot (assignments-snapshot storm-cluster-state sync-callback)

   同步topology代码是消耗时间的事情, 所以实现的时候放在后台执行, 只是将this(function) add到event-manager的queue里面, 后台线程会执行这个函数
   并且在调用assignment获取assignments-snapshot的时候, 将sync-callback set到assignments-callback中去

     (assignments [this callback]
        (when callback
          (reset! assignments-callback callback))
        (get-children cluster-state ASSIGNMENTS-SUBTREE (not-nil? callback)))

By the way, 对于get-children, 是否有callback, 即是否被watch, 读的数据是不一样的, 具体原因不是很清楚, 需要后面看看zk的具体使用

(defn get-children [^CuratorFramework zk ^String path watch?]
  (if watch?
    (.. zk (getChildren) (watched) (forPath (normalize-path path)))
    (.. zk (getChildren) (forPath (normalize-path path)))))

4. 前面说了issue-callback!在执行assignments-callback之前, 会将其清空, 所以如果需要不断的触发, 那么就要不断的设置assignments-callback
    所以作为callback, mk-synchronize-supervisor会先通过assignments-snapshot去重设assignments-callback
    至于为什么要采用这样的机制? 现在还看不清楚