序
本文主要研究一下lettuce的sentinel连接
RedisClient.connectSentinel
lettuce-core-5.0.4.RELEASE-sources.jar!/io/lettuce/core/RedisClient.java
private StatefulRedisSentinelConnection connectSentinel(RedisCodec 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 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，会遍历sentinel，挨个取master获取连接，如果连接不上或抛异常则继续用下一个sentinel获取
- 如果遍历完sentinel都抛异常，则最后抛出RedisConnectionException("Cannot connect to a Redis Sentinel: " + redisURI.getSentinels(),causingException)
- 这里会调用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 > ConnectionFuture 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 channelReadyFuture = new CompletableFuture<>();
Bootstrap redisBootstrap = connectionBuilder.bootstrap();
RedisChannelInitializer initializer = connectionBuilder.build();
redisBootstrap.handler(initializer);
clientResources.nettyCustomizer().afterBootstrapInitialized(redisBootstrap);
CompletableFuture 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 response = new CompletableFuture<>();
response.completeExceptionally(failure);
});
});
return new DefaultConnectionFuture(redisAddress, channelReadyFuture.thenApply(channel -> (T) connectionBuilder
.connection()));
} - 这里initializeChannelAsync的时候，会调用connectionBuilder.socketAddress()方法，进而调用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 connection = connectSentinel(sentinelUri)) {
return connection.async().getMasterAddrByName(sentinelUri.getSentinelMasterId())
.get(timeout.toNanos(), TimeUnit.NANOSECONDS);
}
} - getSocketAddress方法会调用lookupRedis方法，而lookupRedis方法则调用getMasterAddrByName方法，通过sentinel来获取master的ip地址
小结
- redis的sentinel类似于一个master的服务发现中心，假设master有故障，则通过sentinel获取新的master实现failover。
- 而sentinel部署多个来实现高可用，假设一个sentinel挂了，则client端使用下一个sentinel来获取master地址