We have been using Jenkins in AWS, with Simple AD ad the authentication source. 

It has been working fine until 2 days ago when it stopped authenticating. 

On investigation, we get the error message below. No environment changes have been made in the last couple of weeks. 

Error from 'TestDomain' button in plugin global security settings: 

Any Domain Controller is reachable

java.net.SocketException: Socket closed
?? at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:118)??
?? at java.net.SocketOutputStream.write(SocketOutputStream.java:155)??
?? at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:82)??
?? at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:140)??
?? at com.sun.jndi.ldap.Connection.writeRequest(Connection.java:426)??
?? at com.sun.jndi.ldap.Connection.writeRequest(Connection.java:399)??
?? at com.sun.jndi.ldap.LdapClient.ldapBind(LdapClient.java:359)??
?? at com.sun.jndi.ldap.LdapClient.authenticate(LdapClient.java:214)??
Caused: javax.naming.CommunicationException: simple bind failed: ad.bookwana.com:389 [Root exception is java.net.SocketException: Socket closed]

Any suggestions on how to resolve, or further logging I'm happy to provide.