问题描述
在使用APIM配置内部VNET后，如API-1正常配置访问后端服务器的一个接口，而API-2则是通过调用APIM中的API-1来作为backendUrl，会出现500错误。 经过测试，目前这种配置内部集成VNET的情况下，会出现错误。这是一个已知的问题。
错误消息为：Unable to connect to the remote server
而在APIM的开发者门户中测试跟踪接口，则会获取到如下的错误信息：
异常日志
System.Net.WebException: Unable to connect to the remote server ---> System.Net.Sockets.SocketException: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond xxx.xxx.xxx.xxx:443 at System.Net.Sockets.Socket.InternalEndConnect(IAsyncResult asyncResult) at System.Net.Sockets.Socket.EndConnect(IAsyncResult asyncResult) at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Exception& exception) --- End of inner exception stack trace --- at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult) at System.Threading.Tasks.TaskFactory`1.FromAsyncCoreLogic(IAsyncResult iar, Func`2 endFunction, Action`1 endAction, Task`1 promise, Boolean requiresSynchronization) --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.WindowsAzure.ApiManagement.Proxy.Gateway.Handlers.DefaultServiceRequestExecutor.<ExecuteAsync>d__9.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.WindowsAzure.ApiManagement.Proxy.Runtime.Configuration.Models.DefaultHttpBackend.<ProcessAsync>d__5.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.WindowsAzure.ApiManagement.Proxy.Gateway.Policies.IO.CallServiceHandler.<ProcessAsync>d__6.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.WindowsAzure.ApiManagement.Proxy.Gateway.Policies.PipelineWalker.<ExecuteAsync>d__1.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.WindowsAzure.ApiManagement.Proxy.Gateway.Policies.PipelineWalker.<ExecuteAsync>d__1.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.WindowsAzure.ApiManagement.Proxy.Gateway.PipelineExecutor.<ExecuteAsync>d__15.MoveNext()
问题原因
因为APIM 后端实例中, 所有传出流量(包含请求到自己的流量)都被路由到APIM Load Balancer，而不是直接环回接口(Loopback)。 由于SLB的一个局限性，即如果它映射到相同的VM，则不允许建立从后端池中的VM到SLB IP的连接。最终结果是，请求发送到同一APIM服务的API调用开始失败。
解决办法
使用127.0.0.1来代替APIM的域名，并且在API的inbound策略中设置host header，指定值为该APIM的域名。 操作步骤如下：
1：使用127.0.0.1替换APIM域名
2：添加Host header，设置值为APIM域名
设置后全部的 API Policy 为：
<policies> <inbound> <set-header name="Host" exists-action="override"> <value>your apim url here</value> </set-header> </inbound> <backend> <base /> </backend> <outbound> <base /> </outbound> <on-error> <base /> </on-error> </policies>
