sensu-ansible/docs/custom_client_config.md

Custom Client Configuration

When this Ansible role deploys the Sensu client configuration - defined in client.json in the Sensu configuration directory, it works out subscriptions based on group membership within the Ansible inventory. For example, if you have a webservers group within your Ansible inventory, any nodes listed in that group will automatically gain a subscription to webservers within Sensu. This is quite a powerful, convenient feature. It's coupled with the deployment of checks. If you add a new webserver to your infrastructure, Sensu will dynamically pick it up, subscribe it to 'webservers', and deploy webserver checks, without you having to do anything other than add that node into the webservers group within your Ansible inventory. Instantaneous monitoring of your web services!

The above is all very nice and fancy, but, what if you want to define some other properties for a specific node, or override its subscriptions altogether?

Well, I've added the ability to define the client template to deploy with the use of a variable. This means you can deploy a specific client configuration for a single node, or a group, or really whatever you want. A nice property of this is that it's still a Jinja2 template (if you want it to be), so you can still include dynamic data whilst making your desired modifications.

Setting a custom client configuration for a single node

Setting a custom client configuration is done using the sensu_client_config variable. By default, this is set to client.json.j2, which resides within the templates directory of this role.

It's contents (as of writing) are as follows:

{
  "client": {
    "name": "{{ ansible_hostname }}",
    "address": "{{ ansible_default_ipv4['address'] }}",
      "subscriptions": {{ group_names | to_nice_json }}
  }
}

As you can see from above, this configuration's values are all populated using facts.

To override this for a single node, this can be set in the host_vars/node_name.domain.name.yml file.

Let's say we have a node, called custom.cmacr.ae, that we'd like to set the subscriptions value for. We could drop a template somewhere into our Ansible codebase called custom_sensu.client.json.j2 then populate like so:

{
  "client": {
    "name": "{{ ansible_hostname }}",
    "address": "{{ ansible_default_ipv4['address'] }}",
      "subscriptions": [
	    "production",
	    "custom"
      ]
  }
}

Then we would need to set the sensu_client_config variable for custom.cmacr.ae in host_vars/custom.cmacr.ae.yml:

sensu_client_config: path/to/custom_sensu.client.json.j2

This would override this particular node's value(s) for the subscriptions field, therefore changing what monitoring streams it subscribes to.

Setting a custom client configuration for a group

Setting a custom client configuration for a group of nodes is done just the same as a single node instance, just using something like group_vars/group_name.yml instead of host_vars/node.domain.name.yml

Alright, we've got some servers that we don't want to bother all that much in a group called thelazyones. Let's set their keepalive value to a higher value than usual (20 seconds). An easy and logical way of approaching this would be to set group_vars/thelazyones.yml like so:

sensu_client_config: path/to/lazy_sensu.client.json.j2

Where path/to/lazy_sensu.client.json.j2 is a Jinja2 template setting the keepalive value to something greater than usual.