The error code 101505 means the HTTP connection initiated by the ESB has been terminated at the backend. According to the log you can determine whether message has been completely written to the backend prior to the connection close (See [Status SendingCompleted : true] in the log.) Users will usually get an error message such as the following.
type: "Status report"
message: "Runtime Error"
description: "Connection close For : x.x.x.x For Request : Axis2Request [Message ID : urn:uuid:84445830-ed4e-5c15-cd87-bb5b21869e3f] [Status Completed : false] [Status SendingCompleted : true]"
Some Back-end servers do not support persistent connections. So, they tend close down the connections intermediately. If this is the case, then we should disable the Keep-Alive connections at ESB side for such back-ends.
By default Keep-Alive is enabled in WSO2 ESB/APIM. You can switch off this per proxy/api by adding the following property mediator.
<property name="NO_KEEPALIVE" value="true" scope="axis2"/>
But If you need to disable Keep-Alive globally for all the connections initiated from ESB, then that configuration should be specified in transport configuration files.
So, if you are using NIO transport, then add the following property to ESB_HOME/repository/conf/nhttp.properties. But, if you are using Passthru transport, then add the following property to ESB_HOME/repository/conf/passthru-http.properties.