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Loadbalancer dynamically refreshes Nacos server

2022-07-02 08:40:00 【kq1983】

DynamicServerListLoadBalancer

       
        public DynamicServerListLoadBalancer(IClientConfig clientConfig, IRule rule, IPing ping,
        
                                         ServerList<T> serverList, ServerListFilter<T> filter,
        
                                         ServerListUpdater serverListUpdater) {
        
        super(clientConfig, rule, ping);
        
        this.serverListImpl = serverList;
        
        this.filter = filter;
        
        this.serverListUpdater = serverListUpdater;
        
        if (filter instanceof AbstractServerListFilter) {
        
            ((AbstractServerListFilter) filter).setLoadBalancerStats(getLoadBalancerStats());
        
        }
        
        restOfInit(clientConfig); // 
        
    }
       
       
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        void restOfInit(IClientConfig clientConfig) {
        
        boolean primeConnection = this.isEnablePrimingConnections();
        
        // turn this off to avoid duplicated asynchronous priming done in BaseLoadBalancer.setServerList()
        
        this.setEnablePrimingConnections(false);
        
        enableAndInitLearnNewServersFeature(); // serverListUpdater.start(updateAction);
        

        
        updateListOfServers();
        
        if (primeConnection && this.getPrimeConnections() != null) {
        
            this.getPrimeConnections()
        
                    .primeConnections(getReachableServers());
        
        }
        
        this.setEnablePrimingConnections(primeConnection);
        
        LOGGER.info("DynamicServerListLoadBalancer for client {} initialized: {}", clientConfig.getClientName(), this.toString());
        
    }
        

        
 /**
        
     * Feature that lets us add new instances (from AMIs) to the list of
        
     * existing servers that the LB will use Call this method if you want this
        
     * feature enabled
        
     */
        
    public void enableAndInitLearnNewServersFeature() {
        
        LOGGER.info("Using serverListUpdater {}", serverListUpdater.getClass().getSimpleName());
        
        serverListUpdater.start(updateAction); //  Start calling updateAction
        
    }
       
       
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UpdateAction

       
        protected final ServerListUpdater.UpdateAction updateAction = new ServerListUpdater.UpdateAction() {
        
        @Override
        
        public void doUpdate() {
        
            updateListOfServers();
        
        }
        
    };
       
       
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updateListOfServers

       
        public void updateListOfServers() {
        
        List<T> servers = new ArrayList<T>();
        
        if (serverListImpl != null) { // NacosServerList
        
            servers = serverListImpl.getUpdatedListOfServers();
        
            LOGGER.debug("List of Servers for {} obtained from Discovery client: {}",
        
                    getIdentifier(), servers);
        

        
            if (filter != null) {
        
                servers = filter.getFilteredListOfServers(servers);
        
                LOGGER.debug("Filtered List of Servers for {} obtained from Discovery client: {}",
        
                        getIdentifier(), servers);
        
            }
        
        }
        
        updateAllServerList(servers);
        
    }
       
       
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ServerListUpdater

PollingServerListUpdater

PollingServerListUpdater.start

       
        private static long LISTOFSERVERS_CACHE_UPDATE_DELAY = 1000; // msecs;
        
private static int LISTOFSERVERS_CACHE_REPEAT_INTERVAL = 30 * 1000; // msecs;
        

        
@Override
        
    public synchronized void start(final UpdateAction updateAction) {
        
        if (isActive.compareAndSet(false, true)) {
        
            final Runnable wrapperRunnable = new Runnable() {
        
                @Override
        
                public void run() {
        
                    if (!isActive.get()) {
        
                        if (scheduledFuture != null) {
        
                            scheduledFuture.cancel(true);
        
                        }
        
                        return;
        
                    }
        
                    try {
        
                        // DynamicServerListLoadBalancer.doUpdate()
        
                        updateAction.doUpdate();  // updateListOfServers()
        
                        lastUpdated = System.currentTimeMillis();
        
                    } catch (Exception e) {
        
                        logger.warn("Failed one update cycle", e);
        
                    }
        
                }
        
            };
        

        
            scheduledFuture = getRefreshExecutor().scheduleWithFixedDelay(
        
                    wrapperRunnable,
        
                    initialDelayMs, // 1s
        
                    refreshIntervalMs, // 30s
        
                    TimeUnit.MILLISECONDS
        
            );
        
            //  Every time 30s perform 1 Time 
        
        } else {
        
            logger.info("Already active, no-op");
        
        }
        
    }
       
       
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