Camunda 外部客户端：TASK/CLIENT-02002 为请求建立连接时出现异常

Question

我们从实施基于 camunda 的工作流解决方案开始。 目前的设置是这样的：

1. 具有嵌入式 camunda BPM 的 Spring Boot 应用程序（通过 camunda-bpm-spring-boot-starter-rest 和 camunda-bpm-spring-boot-starter-webapp）
2. 带有外部任务客户端的 Spring Boot 应用程序（通过 camunda-external-task-client）

到目前为止一切正常。我们的工作流程正在运行，外部客户正在做他的工作...... 但是过了一会儿（当外部客户端无事可做时）在外部任务客户端的日志中看到异常：

15:49:09.692 [E] [TopicSubscripti] client.logError:70 - TASK/CLIENT-03001 Exception while fetch and lock task.
org.camunda.bpm.client.impl.EngineClientException: TASK/CLIENT-02002 Exception while establishing connection for request 'POST http://localhost:8080/enrichmentservice/api/rest/1.0/rest/external-task/fetchAndLock HTTP/1.1'
at org.camunda.bpm.client.impl.EngineClientLogger.exceptionWhileEstablishingConnection(EngineClientLogger.java:36)
at org.camunda.bpm.client.impl.RequestExecutor.executeRequest(RequestExecutor.java:101)
at org.camunda.bpm.client.impl.RequestExecutor.postRequest(RequestExecutor.java:74)
at org.camunda.bpm.client.impl.EngineClient.fetchAndLock(EngineClient.java:72)
at org.camunda.bpm.client.topic.impl.TopicSubscriptionManager.fetchAndLock(TopicSubscriptionManager.java:135)
at org.camunda.bpm.client.topic.impl.TopicSubscriptionManager.acquire(TopicSubscriptionManager.java:101)
at org.camunda.bpm.client.topic.impl.TopicSubscriptionManager.run(TopicSubscriptionManager.java:87)
at java.lang.Thread.run(Thread.java:748)
Caused by: org.apache.http.NoHttpResponseException: localhost:8080 failed to respond
at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:141)
at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:56)
at org.apache.http.impl.io.AbstractMessageParser.parse(AbstractMessageParser.java:259)
at org.apache.http.impl.DefaultBHttpClientConnection.receiveResponseHeader(DefaultBHttpClientConnection.java:163)
at org.apache.http.impl.conn.CPoolProxy.receiveResponseHeader(CPoolProxy.java:165)
at org.apache.http.protocol.HttpRequestExecutor.doReceiveResponse(HttpRequestExecutor.java:273)
at org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:125)
at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:272)
at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:185)
at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89)
at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:72)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:221)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:165)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:140)
at org.camunda.bpm.client.impl.RequestExecutor.executeRequest(RequestExecutor.java:88)
at org.camunda.bpm.client.impl.RequestExecutor.postRequest(RequestExecutor.java:74)
at org.camunda.bpm.client.impl.EngineClient.fetchAndLock(EngineClient.java:72)
at org.camunda.bpm.client.topic.impl.TopicSubscriptionManager.fetchAndLock(TopicSubscriptionManager.java:135)

这可能是什么原因？ 也许服务器或客户端中的配置错误？ 一句话：外部任务的执行速度很慢（比如10-30秒）

更新： 我创建了一个完整的例子：https://c.gmx.net/@505442085592110443/BIItJGdwTcuWwk7_XqNOXw

要创建错误场景，您必须：

1. 在 spring-boot 项目中启动 ExampleApplication
2. 在 Spring-Boot-Client 项目中启动 ExternalClientApp
3. 等几分钟

外部客户端的日志输出应该是这样的：

Subscribe client for: approveLoan
Subscription done
Subscribe client for: waitTask
Subscription done
pojo before: ObjectValue [value=ExamplePojo [num=123, textVal=some text], isDeserialized=true, serializationDataFormat=application/x-java-serialized-object, objectTypeName=org.camunda.bpm.example.tasks.ExamplePojo, serializedValue=156 chars, isTransient=false]
pojo changed: ObjectValue [value=ExamplePojo [num=123, textVal=external changed], isDeserialized=true, serializationDataFormat=application/x-java-serialized-object, objectTypeName=org.camunda.bpm.example.tasks.ExamplePojo, serializedValue=156 chars, isTransient=false]
The External Task 28 has been completed!
The External Task 32 has been completed! (done = false)
The External Task 39 has been completed! (done = false)
The External Task 46 has been completed! (done = true)
149038 [TopicSubscriptionManager] ERROR org.camunda.bpm.client - TASK/CLIENT-03001 Exception while fetch and lock task.
org.camunda.bpm.client.impl.EngineClientException: TASK/CLIENT-02002 Exception while establishing connection for request 'POST http://localhost:8080/rest/external-task/fetchAndLock HTTP/1.1'
at org.camunda.bpm.client.impl.EngineClientLogger.exceptionWhileEstablishingConnection(EngineClientLogger.java:36)
at org.camunda.bpm.client.impl.RequestExecutor.executeRequest(RequestExecutor.java:101)
at org.camunda.bpm.client.impl.RequestExecutor.postRequest(RequestExecutor.java:74)
at org.camunda.bpm.client.impl.EngineClient.fetchAndLock(EngineClient.java:72)
at org.camunda.bpm.client.topic.impl.TopicSubscriptionManager.fetchAndLock(TopicSubscriptionManager.java:135)
at org.camunda.bpm.client.topic.impl.TopicSubscriptionManager.acquire(TopicSubscriptionManager.java:101)
at org.camunda.bpm.client.topic.impl.TopicSubscriptionManager.run(TopicSubscriptionManager.java:87)
at java.lang.Thread.run(Thread.java:748)
Caused by: org.apache.http.NoHttpResponseException: localhost:8080 failed to respond
at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:141)
at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:56)
at org.apache.http.impl.io.AbstractMessageParser.parse(AbstractMessageParser.java:259)
at org.apache.http.impl.DefaultBHttpClientConnection.receiveResponseHeader(DefaultBHttpClientConnection.java:163)
at org.apache.http.impl.conn.CPoolProxy.receiveResponseHeader(CPoolProxy.java:157)
at org.apache.http.protocol.HttpRequestExecutor.doReceiveResponse(HttpRequestExecutor.java:273)
at org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:125)
at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:272)
at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:185)
at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89)
at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:72)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:221)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:165)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:140)
at org.camunda.bpm.client.impl.RequestExecutor.executeRequest(RequestExecutor.java:88)
... 6 more

Answer 1

在不同的机器/jdk/OS 上对其进行测试后，看起来问题仅出现在 Windows 7 机器上。

我认为错误原因在这里描述：Apache HttpClient Interim Error: NoHttpResponseException

所以服务器正在杀死 http 会话，因为它已经很长时间没有被使用了！

我的解决方法是在客户端配置不同的备份策略，到目前为止我没有任何错误：

tldr：我认为这是外部客户端中的错误，仅在 Win7 上发生，但我找到了解决方法：

    ExternalTaskClient client = ExternalTaskClient.create().baseUrl(baseUrl).backoffStrategy(new ExponentialBackoffStrategy(500L, 2, 30000L)).
            build();

PS 我将其报告为错误：https://app.camunda.com/jira/browse/CAM-10526