Occasionally I'll see orphaned ec2 instances spun up on EC2, that Jenkins never had connected to it. I find the instance ID showing up in the logs with the snippet below. It appears that the createTags call may need some retries because the instance that its telling us that doesn't exist definitely did exist, but perhaps it took Amazon a bit longer than the plugin expected for it to be found.

Status Code: 400, AWS Service: AmazonEC2, AWS Request ID: c97bfd12-8472-4f7f-81ef-c492427bfd63, AWS Error Code: InvalidInstanceID.NotFound, AWS Error Message: The instance ID 'i-7f78974a' does not exist
at com.amazonaws.http.AmazonHttpClient.handleErrorResponse(AmazonHttpClient.java:614)
at com.amazonaws.http.AmazonHttpClient.executeHelper(AmazonHttpClient.java:312)
at com.amazonaws.http.AmazonHttpClient.execute(AmazonHttpClient.java:165)
at com.amazonaws.services.ec2.AmazonEC2Client.invoke(AmazonEC2Client.java:6047)
at com.amazonaws.services.ec2.AmazonEC2Client.createTags(AmazonEC2Client.java:3343)
at hudson.plugins.ec2.SlaveTemplate.provision(SlaveTemplate.java:322)
at hudson.plugins.ec2.EC2Cloud$1.call(EC2Cloud.java:333)
at hudson.plugins.ec2.EC2Cloud$1.call(EC2Cloud.java:329)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:636)