User supplied tooling scripts have the capacity to render
the instance unusable if they hang and never return.
To help avoid this issue it is recommended that all user
tooling scripts be fully tested prior to including them
in a deployable.
If it is not possible to ssh into an instance being
launched on EC2 it is possible the user tooling is
hung and never completed.
If this is encountered the recommendation is to manually
test the user tooling script in a manually launched EC2
For more information refer to:
Bug 816104 - Unable to ssh to the wordpress Apache machine