With version 1.10, the plugin works up to the point where you create a template and it registers a task definition on save. The task def is never registered. Jenkins logs only show the following.

Feb 13, 2017 8:40:36 PM INFO com.cloudbees.jenkins.plugins.amazonecs.ECSCloud
Create cloud jenkins-mt-cloud on ECS cluster arn:aws:ecs:us-east-1:XXXXXXXXXX:cluster/jenkins on the region us-east-1

If I downgrade to version 1.6 it will register the task defintion, and create a task to run on the cluster when you start a job. Though the agent fails to connect, using the default jenkinsci/jnlp-slave image, on the container the JNLP connection fails with the following.

Warning: JnlpProtocol3 is disabled by default, use JNLP_PROTOCOL_OPTS to alter the behavior
Feb 13, 2017 8:25:36 PM hudson.remoting.jnlp.Main createEngine
INFO: Setting up slave: jenkins-mt-cloud-143d4e80eeffb
Feb 13, 2017 8:25:36 PM hudson.remoting.jnlp.Main$CuiListener <init>
INFO: Jenkins agent is running in headless mode.
Feb 13, 2017 8:25:36 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Locating server among http://XXX.XXX.XXX.XXX/
Feb 13, 2017 8:25:36 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Handshaking
Feb 13, 2017 8:25:36 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Connecting to XXX.XXX.XXX.XXX:5000
Feb 13, 2017 8:25:36 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Protocol JNLP3-connect is not enabled, skipping
Feb 13, 2017 8:25:36 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Trying protocol: JNLP2-connect
Feb 13, 2017 8:25:36 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Server didn't accept the handshake: HTTP/1.1 400 Bad Request
Feb 13, 2017 8:25:36 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Connecting to XXX.XXX.XXX.XXX:5000
Feb 13, 2017 8:25:36 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Trying protocol: JNLP-connect
Feb 13, 2017 8:25:36 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Server didn't accept the handshake: HTTP/1.1 400 Bad Request
Feb 13, 2017 8:25:36 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Connecting to XXX.XXX.XXX.XXX:5000
Feb 13, 2017 8:25:36 PM hudson.remoting.jnlp.Main$CuiListener error
SEVERE: The server rejected the connection: None of the protocols were accepted
java.lang.Exception: The server rejected the connection: None of the protocols were accepted
at hudson.remoting.Engine.onConnectionRejected(Engine.java:353)
at hudson.remoting.Engine.run(Engine.java:325)