/usr/share/tripleo-heat-templates/environments/docker-network.yaml is in python-tripleo-heat-templates 5.2.0-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | resource_registry:
OS::TripleO::Compute::Net::SoftwareConfig: ../net-config-bridge.yaml
|