title: Docker-plugin on Jenkins fails to Test Connection
body: <p>I have ubuntu server with installed docker on it. 
  I have deployed Jenkins on Docker with installed docker-plugin on it. </p>
  
  <p>I am trying to add Cloud-docker, with params:</p>
  
  <p>jenkins.version is 1.597</p>
  
  <p>name: docker
  Docker Url: 172.17.42.1:4243
  connection timeout: 5
  read timeout: 15</p>
  
  <p>But I am getting all the time Connection refused error during Test Connection:</p>
  
  <blockquote>
    <p>javax.servlet.ServletException: javax.ws.rs.ProcessingException:
    java.net.ConnectException: Connection refused     at
    org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:796)   at
    org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)  at
    org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:249)    at
    org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
      at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)  at
    org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)  at
    org.kohsuke.stapler.Stapler.invoke(Stapler.java:649)  at
    org.kohsuke.stapler.Stapler.service(Stapler.java:238)     at
    javax.servlet.http.HttpServlet.service(HttpServlet.java:848)  at
    org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:686)
      at
    org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1494)
      at
    hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:123)
      at
    hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:114)
      at
    org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
      at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:48)   at
    org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
      at
    hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
      at
    hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
      at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:164)     at
    org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
      at
    org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:49)
      at
    org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
      at
    hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:81)
      at
    org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
      at
    org.kohsuke.stapler.DiagnosticThreadNameFilter.doFilter(DiagnosticThreadNameFilter.java:30)
      at
    org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1474)
      at
    org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:499)
      at
    org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:137)
      at
    org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:533)
      at
    org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231)
      at
    org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1086)
      at
    org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:428)
      at
    org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193)
      at
    org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1020)
      at
    org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135)
      at
    org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116)
      at org.eclipse.jetty.server.Server.handle(Server.java:370)  at
    org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:489)
      at
    org.eclipse.jetty.server.AbstractHttpConnection.content(AbstractHttpConnection.java:960)
      at
    org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.content(AbstractHttpConnection.java:1021)
      at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:865)
      at
    org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:240)
      at
    org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82)
      at
    org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:668)
      at
    org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:52)
      at
    winstone.BoundedExecutorService$1.run(BoundedExecutorService.java:77)
      at
    java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
      at
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
      at java.lang.Thread.run(Thread.java:745) Caused by:
    javax.ws.rs.ProcessingException: java.net.ConnectException: Connection
    refused   at
    org.glassfish.jersey.client.HttpUrlConnector.apply(HttpUrlConnector.java:184)
      at
    org.glassfish.jersey.client.ClientRuntime.invoke(ClientRuntime.java:227)
      at
    org.glassfish.jersey.client.JerseyInvocation$3.call(JerseyInvocation.java:693)
      at org.glassfish.jersey.internal.Errors.process(Errors.java:315)    at
    org.glassfish.jersey.internal.Errors.process(Errors.java:297)     at
    org.glassfish.jersey.internal.Errors.process(Errors.java:228)     at
    org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:422)
      at
    org.glassfish.jersey.client.JerseyInvocation.invoke(JerseyInvocation.java:689)
      at
    org.glassfish.jersey.client.JerseyInvocation$Builder.method(JerseyInvocation.java:405)
      at
    org.glassfish.jersey.client.proxy.WebResourceFactory.invoke(WebResourceFactory.java:318)
      at com.sun.proxy.$Proxy51.version(Unknown Source)   at
    com.nirima.docker.client.DockerClient$System.version(DockerClient.java:116)
      at
    com.nirima.jenkins.plugins.docker.DockerCloud$DescriptorImpl.doTestConnection(DockerCloud.java:341)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)  at
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
      at
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:606)     at
    org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:298)
      at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:161)    at
    org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:96)
      at org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:121)   at
    org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
      at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)  ... 48
    more Caused by: java.net.ConnectException: Connection refused     at
    java.net.PlainSocketImpl.socketConnect(Native Method)     at
    java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
      at
    java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
      at
    java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
      at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)   at
    java.net.Socket.connect(Socket.java:579)  at
    sun.net.NetworkClient.doConnect(NetworkClient.java:175)   at
    sun.net.www.http.HttpClient.openServer(HttpClient.java:432)   at
    sun.net.www.http.HttpClient.openServer(HttpClient.java:527)   at
    sun.net.www.http.HttpClient.(HttpClient.java:211)   at
    sun.net.www.http.HttpClient.New(HttpClient.java:308)  at
    sun.net.www.http.HttpClient.New(HttpClient.java:326)  at
    sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:996)
      at
    sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:932)
      at
    sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:850)
      at
    sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1300)
      at
    java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:468)
      at
    org.glassfish.jersey.client.HttpUrlConnector._apply(HttpUrlConnector.java:276)
      at
    org.glassfish.jersey.client.HttpUrlConnector.apply(HttpUrlConnector.java:182)
      ... 70 more</p>
  </blockquote>
  
  <p>what could be wrong?</p>
  
  <p>thanks</p>