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* Added support for Graviton instances.
* Removed ``other_instance_types`` as option for ``behavior_on_capacity_limit``. It will fall back to ``wait_and_retry``.
* Multiple instance types can be specified in the configuration. If ``spot_instance`` is enabled, Tibanna will run the workflow on the instance with the highest available capacity. If ``spot_instance`` is disabled, it will run the workflow on the cheapest instance in the list.
* Instead of using the ``run_instance`` command we switch to EC2 fleets (in instant mode) to start up instances.