Storm-源码分析- Storm中Zookeeper的使用

xiaoxiao2024-05-09 7

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

本文章摘自博客园，原文发布日期：2013-06-26