In the Heat-File (yaml) the creation of the dcae_vm_key is defined:

dcae_vm_key:
...
params:
{{ base: { get_param: dcae_key_name }}}
{{ rand: { get_resource: random-str }}}
{{ public_key: { get_param: dcae_pub_key }}}
{{ save_private_key: true}}

In the definition of the dcae VM the private key should be extrated and imported to the VM:
{{ _private_key_: { get_attr: [ dcae_vm_key, private_key ] }}}

Problem: The private key extraction is not possible, when a public key is given in the dcae_vm_key definition (see https://docs.openstack.org/heat/latest/template_guide/openstack.html#OS::Nova::KeyPair) 

So the attribute _private_key_ is empty and the Startup of the DCAE docker container fails.