blockinfile keeps adding the block

Question

I'd like to add a block of text to my ElasticSearch configuration using blockinfile, but every time I run my playbook, the block gets added to the file -- even when it already exists. This is a problem because ElasticSearch doesn't just take the last value, it chokes on startup saying "you have multiple entries for this value" (or something similar).

My play looks like this:

  - name: configure elasticsearch
    blockinfile:
      dest: /etc/elasticsearch/elasticsearch.yml
      marker: "## added by ansible configuration"
      block: |
        network.host: 0.0.0.0
        path.data: /var/lib
        path.logs: /var/log/elasticsearch
        path.repo: /home/chris/elastic-backups
      state: present

But after running my playbook a second time, my elasticsearch.yml file looks like:

## added by ansible configuration
network.host: 0.0.0.0
path.data: /var/lib
path.logs: /var/log/elasticsearch
path.repo: /home/chris/elastic-backups
## added by ansible configuration
network.host: 0.0.0.0
path.data: /var/lib
path.logs: /var/log/elasticsearch
path.repo: /home/chris/elastic-backups
## added by ansible configuration

Is there a way to only add the block if it does not exist yet?

Answer 1

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.

Answer 2

The accepted answer is correct and straightforward.

But also marker string should not contain line breaks like \n, otherwise, Ansible will keep adding the block. Sounds like a bug for me