There are some cases where when the EC2 plugin gets triggered to spin up a new node, the below output appears. The temp fix is to just relaunch the agent and that fixes itself, however, this always requires manual intervention. If it fails, it will keep on spinning up new nodes and constantly fail for some reason. 

ssh -o StrictHostKeyChecking=no -i /tmp/ec2_4311748328328850426.pem ubuntu@null -p 22  java  -jar /tmp/remoting.jar -workDir /var/lib/jenkins
ssh: Could not resolve hostname null: Temporary failure in name resolution