即使无法访问MQTT服务器，如何启动骆驼 [英] How to start camel even if the MQTT server is not reachable
问题描述
我想使我的Apache Camel应用程序更具弹性并即使在无法访问MQTT代理时也可以启动.我们正在可能不稳定的Internet连接的物联网设备上使用Camel，我希望即使没有Internet访问，我们的应用程序也可以启动.
I would like to make my Apache Camel application to be more resilient and start even when the MQTT broker is not reachable. We are using Camel on IoT devices with a possibly unstable internet connection and I want our application to start even without internet access.
一条示例路线如下:
from("timer:heartbeat?period=5000")
.routeId("send heartbeat")
.setBody(simple("Hello World!"))
.to("paho:myhostnome/heartbeat?brokerUrl={{broker.url}}")
只要MQTT服务器可用，它就可以正常工作.但是，当服务器无法访问时，在预热PahoEndpoint时上下文将失败.
This works fine as long as the MQTT server is available. However when the server is not reachable, the context fails while warming up the PahoEndpoint.
Caused by: org.apache.camel.FailedToCreateRouteException: Failed to create route send heartbeat: Route(send heartbeat)[[From[timer:heartbeat?period={{heartbe... because of Unable to connect to server
at org.apache.camel.impl.RouteService.warmUp(RouteService.java:147) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.doWarmUpRoutes(DefaultCamelContext.java:3758) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.safelyStartRouteServices(DefaultCamelContext.java:3665) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.doStartOrResumeRoutes(DefaultCamelContext.java:3451) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.doStartCamel(DefaultCamelContext.java:3305) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.access$000(DefaultCamelContext.java:202) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext$2.call(DefaultCamelContext.java:3089) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext$2.call(DefaultCamelContext.java:3085) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.doWithDefinedClassLoader(DefaultCamelContext.java:3108) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.doStart(DefaultCamelContext.java:3085) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.support.ServiceSupport.start(ServiceSupport.java:61) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.start(DefaultCamelContext.java:3022) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.spring.boot.RoutesCollector.maybeStart(RoutesCollector.java:242) ~[camel-spring-boot-2.19.3.jar:2.19.3]
at org.apache.camel.spring.boot.RoutesCollector.onApplicationEvent(RoutesCollector.java:217) ~[camel-spring-boot-2.19.3.jar:2.19.3]
... 13 common frames omitted
Caused by: org.eclipse.paho.client.mqttv3.MqttException: Unable to connect to server
at org.eclipse.paho.client.mqttv3.internal.TCPNetworkModule.start(TCPNetworkModule.java:79) ~[org.eclipse.paho.client.mqttv3-1.1.0.jar:na]
at org.eclipse.paho.client.mqttv3.internal.ClientComms$ConnectBG.run(ClientComms.java:650) ~[org.eclipse.paho.client.mqttv3-1.1.0.jar:na]
at java.lang.Thread.run(Thread.java:745) ~[na:1.8.0_121]
Caused by: java.net.ConnectException: Connection refused (Connection refused)
at java.net.PlainSocketImpl.socketConnect(Native Method) ~[na:1.8.0_121]
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350) ~[na:1.8.0_121]
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206) ~[na:1.8.0_121]
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188) ~[na:1.8.0_121]
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) ~[na:1.8.0_121]
at java.net.Socket.connect(Socket.java:589) ~[na:1.8.0_121]
at org.eclipse.paho.client.mqttv3.internal.TCPNetworkModule.start(TCPNetworkModule.java:70) ~[org.eclipse.paho.client.mqttv3-1.1.0.jar:na]
我的第一个想法是在涉及Paho的所有路由上禁用自动启动，并手动启动它们.由于PahoEndpoint已启动，因此即使路由本身未启动也无法使用.
My first idea was to disable auto startup on all routes involving Paho and start them manually. This does not work as the PahoEndpoint is started even when the route itself is not started.
我正在寻找一种替代方法来解决此问题.
I'm now looking for an alternative approach to handle this problem.
推荐答案
Apache Camel 2.20及更高版本具有一项新功能，可让启动过程使用 superviser控制器来运行，该控制器将从CamelContext本身.这样可以设置更高级的配置，以让控制器处理错误，并尝试重试启动失败的路由等.
Apache Camel 2.20 onwards comes with a new functionality to let the startup procedure run using a superviser controller that takes over starting up from CamelContext itself. This allows to setup more advanced configuration to let the controller handle errors, and attempt to retry starting the failed routes etc.
有一个通过Spring Boot配置它的示例，但是您也可以从Java API配置它:
There is an example where its configured via Spring Boot, but you can configure it from Java API as well: https://github.com/apache/camel/tree/master/examples/camel-example-spring-boot-supervising-route-controller
在即将发布的版本中，我们将改进此新功能. 对于较早版本的Camel，那么它通常是可能提供或不提供任何重试机制的组件本身，您需要进行配置，而不是快速失败.
In the upcoming releases we will improve on this new functionality. For older versions of Camel then its often the component itself that may or may not offer any kind of retry mechanism, you need to configure, instead of failing fast.
这篇关于即使无法访问MQTT服务器，如何启动骆驼的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
