异常堆栈

java.io.IOException: Connection reset by peer
    at sun.nio.ch.FileDispatcherImpl.read0(Native Method)
    at sun.nio.ch.SocketDispatcher.read(SocketDispatcher.java:39)
    at sun.nio.ch.IOUtil.readIntoNativeBuffer(IOUtil.java:223)
    at sun.nio.ch.IOUtil.read(IOUtil.java:197)
    at sun.nio.ch.SocketChannelImpl.read(SocketChannelImpl.java:379)
    at org.apache.http.impl.nio.reactor.SessionInputBufferImpl.fill(SessionInputBufferImpl.java:231)
    at org.apache.http.impl.nio.codecs.AbstractMessageParser.fillBuffer(AbstractMessageParser.java:136)
    at org.apache.http.impl.nio.DefaultNHttpClientConnection.consumeInput(DefaultNHttpClientConnection.java:241)
    at org.apache.http.impl.nio.client.InternalIODispatch.onInputReady(InternalIODispatch.java:81)
    at org.apache.http.impl.nio.client.InternalIODispatch.onInputReady(InternalIODispatch.java:39)
    at org.apache.http.impl.nio.reactor.AbstractIODispatch.inputReady(AbstractIODispatch.java:114)
    at org.apache.http.impl.nio.reactor.BaseIOReactor.readable(BaseIOReactor.java:162)
    at org.apache.http.impl.nio.reactor.AbstractIOReactor.processEvent(AbstractIOReactor.java:337)
    at org.apache.http.impl.nio.reactor.AbstractIOReactor.processEvents(AbstractIOReactor.java:315)
    at org.apache.http.impl.nio.reactor.AbstractIOReactor.execute(AbstractIOReactor.java:276)
    at org.apache.http.impl.nio.reactor.BaseIOReactor.execute(BaseIOReactor.java:104)
    at org.apache.http.impl.nio.reactor.AbstractMultiworkerIOReactor$Worker.run(AbstractMultiworkerIOReactor.java:591)
    at java.lang.Thread.run(Thread.java:748)
    Suppressed: java.io.IOException: Connection reset by peer
        ... 18 more
        Suppressed: java.io.IOException: Connection reset by peer
            ... 18 more

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1.长连接请求

以浏览器发起请求为例，在Request Headers中会包含Connection: keep-alive信息

image

当tomcat收到浏览器端的长连接请求后，如在限制范围内，则会在Response Headers中返回Connection: keep-alive以保持连接不断开

image

如要断开长连接则在Request Headers中的信息为Connection: close

2、了解了长连接原理后查看源码ElasticsearchSinkBase.java的创建restclient的open

    @Override
    public void open(Configuration parameters) throws Exception {
        client = callBridge.createClient(userConfig);
        bulkProcessor = buildBulkProcessor(new BulkProcessorListener());
        requestIndexer = callBridge.createBulkProcessorIndexer(bulkProcessor, flushOnCheckpoint, numPendingRequests);
        failureRequestIndexer = new BufferingNoOpRequestIndexer();
    }

    @Override
    public RestHighLevelClient createClient(Map<String, String> clientConfig) throws IOException {
        RestClientBuilder builder = RestClient.builder(httpHosts.toArray(new HttpHost[httpHosts.size()]));
        restClientFactory.configureRestClientBuilder(builder);

        RestHighLevelClient rhlClient = new RestHighLevelClient(builder);

        if (LOG.isInfoEnabled()) {
            LOG.info("Pinging Elasticsearch cluster via hosts {} ...", httpHosts);
        }

        if (!rhlClient.ping(RequestOptions.DEFAULT)) {
            throw new RuntimeException("There are no reachable Elasticsearch nodes!");
        }

        if (LOG.isInfoEnabled()) {
            LOG.info("Created Elasticsearch RestHighLevelClient connected to {}", httpHosts.toString());
        }

        return rhlClient;
    }

可以看到这里创建了一个RestHighLevelClient，继续查看构造函数

 /**
     * Creates a {@link RestHighLevelClient} given the low level {@link RestClientBuilder} that allows to build the
     * {@link RestClient} to be used to perform requests.
     */
    public RestHighLevelClient(RestClientBuilder restClientBuilder) {
        this(restClientBuilder, Collections.emptyList());
    }

    /**
     * Creates a {@link RestHighLevelClient} given the low level {@link RestClientBuilder} that allows to build the
     * {@link RestClient} to be used to perform requests and parsers for custom response sections added to Elasticsearch through plugins.
     */
    protected RestHighLevelClient(RestClientBuilder restClientBuilder, List<NamedXContentRegistry.Entry> namedXContentEntries) {
        this(restClientBuilder.build(), RestClient::close, namedXContentEntries);
    }

    //进入restClientBuilder.build()

   /**
     * Creates a new {@link RestClient} based on the provided configuration.
     */
    public RestClient build() {
        if (failureListener == null) {
            failureListener = new RestClient.FailureListener();
        }
        CloseableHttpAsyncClient httpClient = AccessController.doPrivileged(
            (PrivilegedAction<CloseableHttpAsyncClient>) this::createHttpClient);
        RestClient restClient = new RestClient(httpClient, defaultHeaders, nodes,
                pathPrefix, failureListener, nodeSelector, strictDeprecationMode);
        httpClient.start();
        return restClient;
    }
    //进入 this::createHttpClient
        private CloseableHttpAsyncClient createHttpClient() {
        //default timeouts are all infinite
        RequestConfig.Builder requestConfigBuilder = RequestConfig.custom()
                .setConnectTimeout(DEFAULT_CONNECT_TIMEOUT_MILLIS)
                .setSocketTimeout(DEFAULT_SOCKET_TIMEOUT_MILLIS);
        if (requestConfigCallback != null) {
            requestConfigBuilder = requestConfigCallback.customizeRequestConfig(requestConfigBuilder);
        }

        try {
            HttpAsyncClientBuilder httpClientBuilder = HttpAsyncClientBuilder.create().setDefaultRequestConfig(requestConfigBuilder.build())
                //default settings for connection pooling may be too constraining
                .setMaxConnPerRoute(DEFAULT_MAX_CONN_PER_ROUTE).setMaxConnTotal(DEFAULT_MAX_CONN_TOTAL)
                .setSSLContext(SSLContext.getDefault())
                .setTargetAuthenticationStrategy(new PersistentCredentialsAuthenticationStrategy());
            if (httpClientConfigCallback != null) {
                httpClientBuilder = httpClientConfigCallback.customizeHttpClient(httpClientBuilder);
            }

            final HttpAsyncClientBuilder finalBuilder = httpClientBuilder;
            return AccessController.doPrivileged((PrivilegedAction<CloseableHttpAsyncClient>) finalBuilder::build);
        } catch (NoSuchAlgorithmException e) {
            throw new IllegalStateException("could not create the default ssl context", e);
        }
    }
    
    // finalBuilder::build可以看到
   ConnectionKeepAliveStrategy keepAliveStrategy = this.keepAliveStrategy;
        if (keepAliveStrategy == null) {
            keepAliveStrategy = DefaultConnectionKeepAliveStrategy.INSTANCE;
        }

如果客户端使用的是apache httpclient 4.x版本，默认的keep-alive是读取response heade中Keep-Alive字段,没有的话就是无限（代码中返回-1）。"If the Keep-Alive header is not present in the response, HttpClient assumes the connection can be kept alive indefinitely"，详细代码DefaultConnectionKeepAliveStrategy.class类设置的，代码如下：

@Contract(threading = ThreadingBehavior.IMMUTABLE)
public class DefaultConnectionKeepAliveStrategy implements ConnectionKeepAliveStrategy {

    public static final DefaultConnectionKeepAliveStrategy INSTANCE = new DefaultConnectionKeepAliveStrategy();

    @Override
    public long getKeepAliveDuration(final HttpResponse response, final HttpContext context) {
        Args.notNull(response, "HTTP response");
        final HeaderElementIterator it = new BasicHeaderElementIterator(
                response.headerIterator(HTTP.CONN_KEEP_ALIVE));
        while (it.hasNext()) {
            final HeaderElement he = it.nextElement();
            final String param = he.getName();
            final String value = he.getValue();
            if (value != null && param.equalsIgnoreCase("timeout")) {
                try {
                    return Long.parseLong(value) * 1000;
                } catch(final NumberFormatException ignore) {
                }
            }
        }
        return -1;
    }
}

网上搜了一下这个的含义，具体如下

image.png

这里需要自定义实现ConnectionKeepAliveStrategy

public class CustomConnectionKeepAliveStrategy extends DefaultConnectionKeepAliveStrategy {
    /**
     * 最大keep alive的时间（分钟）
     * 这里默认为10分钟，可以根据实际情况设置。可以观察客户端机器状态为TIME_WAIT的TCP连接数，如果太多，可以增大此值。
     */
    private final static long MAX_KEEP_ALIVE_MINUTES = 10;

    public static final CustomConnectionKeepAliveStrategy INSTANCE = new CustomConnectionKeepAliveStrategy();

    private CustomConnectionKeepAliveStrategy() {
        super();
    }

    @Override
    public long getKeepAliveDuration(HttpResponse response, HttpContext context) {
        long keepAliveDuration = super.getKeepAliveDuration(response, context);
        // <0 为无限期keepalive,将无限期替换成一个默认的时间
        if (keepAliveDuration < 0) {
            return TimeUnit.MINUTES.toMillis(MAX_KEEP_ALIVE_MINUTES);
        }
        return keepAliveDuration;
    }
}

// 在客户端创建的时候设置KeepAlive策略为自定义策略即可
esSinkBuilder.setRestClientFactory(restClientBuilder -> {
            restClientBuilder.setHttpClientConfigCallback(httpClientBuilder -> {
httpClientBuilder.setKeepAliveStrategy(CustomConnectionKeepAliveStrategy.INSTANCE);
                return httpClientBuilder;
            });
        });

参考链接：【Elasticsearch】解决Elasticsearch HTTP方式查询报SocketTimeoutException的问题 Connection reset by peer
两种由java http长连接(keep-alive)导致的问题
Connection keep alive strategy