YAML files are central to installing and upkeep of the Openstack. YAML stands for Yet Another Markup Language. It is considered to be human readable too. Columns for subcategories on new lines are set spaces. Non-standard characters can also cause errors. It is not always clear what the errors are. Openstack scripts run until they fall.
To validate your YAML, you can paste your file contents into https://codebeautify.org/yaml-validator
From each server you can run a python single line script which inputs your YAML file. If your YAML is fine the script exits without issue, however if you have a single mistake it throws many errors. You need to only look at the last lines of the output, these state which line in YAML is incorrect. The column number given is often incorrect. Replace the path and file name with whatever YAML file you have edited.
python -c 'import yaml,sys;yaml.safe_load(sys.stdin)' < /home/stack/custom-templates.12/ceph.yaml