as-create-auto-scaling-group are thin wrappers around the AWS SDK for Java; you can read all the commands placed in /opt/aws/apitools/as/bin but they eventually just invoke Java with a classpath set and invoke
com.amazon.webservices.Cli or so.
Thus, the CLI commands are essentially documented by the Java API Reference. In particular, the
as-* family reflects operations on
com.amazonaws.services.autoscaling which consume data types in
What I was specifically looking for was documentation on the
--grace-period operations, and
....model.CreateAutoScalingGroupRequest finally has me covered. Health check can be either 'EC2' or 'ELB', to select either the standard (and presumably default) EC2 "is the host hardware alive? can we ping the vm?" instance checks; or the "can we access this URL on the instance's http server?" health check configured in setting up an elastic load balancer. Respectively.
--grace-period is the time delay between starting up a new instance, and when auto scaling is allowed to start asking for its health.