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本文主要研究一下lettuce的sentinel連接

RedisClient.connectSentinel

lettuce-core-5.0.4.RELEASE-sources.jar!/io/lettuce/core/RedisClient.java

    private <K, V> StatefulRedisSentinelConnection<K, V> connectSentinel(RedisCodec<K, V> codec, RedisURI redisURI,
            Duration timeout) {
        assertNotNull(codec);
        checkValidRedisURI(redisURI);

        ConnectionBuilder connectionBuilder = ConnectionBuilder.connectionBuilder();
        connectionBuilder.clientOptions(ClientOptions.copyOf(getOptions()));
        connectionBuilder.clientResources(clientResources);

        DefaultEndpoint endpoint = new DefaultEndpoint(clientOptions);

        StatefulRedisSentinelConnectionImpl<K, V> connection = newStatefulRedisSentinelConnection(endpoint, codec, timeout);

        logger.debug("Trying to get a Redis Sentinel connection for one of: " + redisURI.getSentinels());

        connectionBuilder.endpoint(endpoint).commandHandler(() -> new CommandHandler(clientOptions, clientResources, endpoint))
                .connection(connection);
        connectionBuilder(getSocketAddressSupplier(redisURI), connectionBuilder, redisURI);

        if (clientOptions.isPingBeforeActivateConnection()) {
            connectionBuilder.enablePingBeforeConnect();
        }

        if (redisURI.getSentinels().isEmpty() && (isNotEmpty(redisURI.getHost()) || !isEmpty(redisURI.getSocket()))) {
            channelType(connectionBuilder, redisURI);
            try {
                getConnection(initializeChannelAsync(connectionBuilder));
            } catch (RuntimeException e) {
                connection.close();
                throw e;
            }
        } else {

            boolean connected = false;
            boolean first = true;
            Exception causingException = null;
            validateUrisAreOfSameConnectionType(redisURI.getSentinels());

            for (RedisURI uri : redisURI.getSentinels()) {
                if (first) {
                    channelType(connectionBuilder, uri);
                    first = false;
                }
                connectionBuilder.socketAddressSupplier(getSocketAddressSupplier(uri));

                if (logger.isDebugEnabled()) {
                    SocketAddress socketAddress = SocketAddressResolver.resolve(uri, clientResources.dnsResolver());
                    logger.debug("Connecting to Redis Sentinel, address: " + socketAddress);
                }
                try {
                    getConnection(initializeChannelAsync(connectionBuilder));
                    connected = true;
                    break;
                } catch (Exception e) {
                    logger.warn("Cannot connect Redis Sentinel at " + uri + ": " + e.toString());
                    causingException = e;
                }
            }

            if (!connected) {
                connection.close();
                throw new RedisConnectionException("Cannot connect to a Redis Sentinel: " + redisURI.getSentinels(),
                        causingException);
            }
        }

        if (LettuceStrings.isNotEmpty(redisURI.getClientName())) {
            connection.setClientName(redisURI.getClientName());
        }

        return connection;
    }

• connectSentinel方法，會(huì)遍歷sentinel，挨個(gè)取master獲取連接，如果連接不上或拋異常則繼續(xù)用下一個(gè)sentinel獲取
• 如果遍歷完sentinel都拋異常，則最后拋出RedisConnectionException("Cannot connect to a Redis Sentinel: " + redisURI.getSentinels(),causingException)
• 這里會(huì)調(diào)用AbstractRedisClient的initializeChannelAsync方法

AbstractRedisClient.initializeChannelAsync

lettuce-core-5.0.4.RELEASE-sources.jar!/io/lettuce/core/AbstractRedisClient.java

    /**
     * Connect and initialize a channel from {@link ConnectionBuilder}.
     *
     * @param connectionBuilder must not be {@literal null}.
     * @return the {@link ConnectionFuture} to synchronize the connection process.
     * @since 4.4
     */
    @SuppressWarnings("unchecked")
    protected <K, V, T extends RedisChannelHandler<K, V>> ConnectionFuture<T> initializeChannelAsync(
            ConnectionBuilder connectionBuilder) {

        SocketAddress redisAddress = connectionBuilder.socketAddress();

        if (clientResources.eventExecutorGroup().isShuttingDown()) {
            throw new IllegalStateException("Cannot connect, Event executor group is terminated.");
        }

        logger.debug("Connecting to Redis at {}", redisAddress);

        CompletableFuture<Channel> channelReadyFuture = new CompletableFuture<>();
        Bootstrap redisBootstrap = connectionBuilder.bootstrap();

        RedisChannelInitializer initializer = connectionBuilder.build();
        redisBootstrap.handler(initializer);

        clientResources.nettyCustomizer().afterBootstrapInitialized(redisBootstrap);
        CompletableFuture<Boolean> initFuture = initializer.channelInitialized();
        ChannelFuture connectFuture = redisBootstrap.connect(redisAddress);

        connectFuture.addListener(future -> {

            if (!future.isSuccess()) {

                logger.debug("Connecting to Redis at {}: {}", redisAddress, future.cause());
                connectionBuilder.endpoint().initialState();
                channelReadyFuture.completeExceptionally(future.cause());
                return;
            }

            initFuture.whenComplete((success, throwable) -> {

                if (throwable == null) {
                    logger.debug("Connecting to Redis at {}: Success", redisAddress);
                    RedisChannelHandler<?, ?> connection = connectionBuilder.connection();
                    connection.registerCloseables(closeableResources, connection);
                    channelReadyFuture.complete(connectFuture.channel());
                    return;
                }

                logger.debug("Connecting to Redis at {}, initialization: {}", redisAddress, throwable);
                connectionBuilder.endpoint().initialState();
                Throwable failure;

                if (throwable instanceof RedisConnectionException) {
                    failure = throwable;
                } else if (throwable instanceof TimeoutException) {
                    failure = new RedisConnectionException("Could not initialize channel within "
                            + connectionBuilder.getTimeout(), throwable);
                } else {
                    failure = throwable;
                }
                channelReadyFuture.completeExceptionally(failure);

                CompletableFuture<Boolean> response = new CompletableFuture<>();
                response.completeExceptionally(failure);

            });
        });

        return new DefaultConnectionFuture<T>(redisAddress, channelReadyFuture.thenApply(channel -> (T) connectionBuilder
                .connection()));
    }

• 這里initializeChannelAsync的時(shí)候，會(huì)調(diào)用connectionBuilder.socketAddress()方法，進(jìn)而調(diào)用RedisClient的getSocketAddress方法

RedisClient.getSocketAddress

lettuce-core-5.0.4.RELEASE-sources.jar!/io/lettuce/core/RedisClient.java

    protected SocketAddress getSocketAddress(RedisURI redisURI) throws InterruptedException, TimeoutException,
            ExecutionException {
        SocketAddress redisAddress;

        if (redisURI.getSentinelMasterId() != null && !redisURI.getSentinels().isEmpty()) {
            logger.debug("Connecting to Redis using Sentinels {}, MasterId {}", redisURI.getSentinels(),
                    redisURI.getSentinelMasterId());
            redisAddress = lookupRedis(redisURI);

            if (redisAddress == null) {
                throw new RedisConnectionException("Cannot provide redisAddress using sentinel for masterId "
                        + redisURI.getSentinelMasterId());
            }

        } else {
            redisAddress = SocketAddressResolver.resolve(redisURI, clientResources.dnsResolver());
        }
        return redisAddress;
    }

    private SocketAddress lookupRedis(RedisURI sentinelUri) throws InterruptedException, TimeoutException, ExecutionException {
        try (StatefulRedisSentinelConnection<String, String> connection = connectSentinel(sentinelUri)) {
            return connection.async().getMasterAddrByName(sentinelUri.getSentinelMasterId())
                    .get(timeout.toNanos(), TimeUnit.NANOSECONDS);
        }
    }

• getSocketAddress方法會(huì)調(diào)用lookupRedis方法，而lookupRedis方法則調(diào)用getMasterAddrByName方法，通過sentinel來獲取master的ip地址

小結(jié)

• redis的sentinel類似于一個(gè)master的服務(wù)發(fā)現(xiàn)中心，假設(shè)master有故障，則通過sentinel獲取新的master實(shí)現(xiàn)failover。
• 而sentinel部署多個(gè)來實(shí)現(xiàn)高可用，假設(shè)一個(gè)sentinel掛了，則client端使用下一個(gè)sentinel來獲取master地址

doc

• lettuce Redis-Sentinel