You should specify {mark} keyword in the marker parameter:
marker: "## {mark} added by ansible (configuration elasticsearch)"This will cause Ansible to insert a line at the beginning and at the end of the block replacing {mark} accordingly with BEGIN and END:
## BEGIN added by ansible (configuration elasticsearch)
network.host: 0.0.0.0
path.data: /var/lib
path.logs: /var/log/elasticsearch
path.repo: /home/chris/elastic-backups
## END added by ansible (configuration elasticsearch)Otherwise Ansible has no clue, where the block starts and where it ends, so on every run it considers the block is not present and inserts a new one.