Conditional actions based on host type?

[Mark Farrington]

Hi,

New to ansible and looking for advice.

I have an action inside a task (I think that is correct terminology).

Something like this:

 - name: Cloudwatch deploy agent configuration for webserver

      template:

          src: templates/web-inst.json

          dest: "/opt/aws/amazon-cloudwatch-agent/bin/config.json"

          mode: 0644

      tags:

          - config

The task is used to install AWS cloudwatch on web servers and this action is to just apply the config.   Now I want to extend this task to other types or servers (Lets say app server).

So I want to add another config action like this:

 - name: Cloudwatch deploy agent configuration for App Server

      template:

          src: templates/app-inst.json

          dest: "/opt/aws/amazon-cloudwatch-agent/bin/config.json"

          mode: 0644

      tags:

          - config

So, now I have two code blocks for configuration (One for each type of server).    How do I conditionally apply the correct config based on the host type?

I currently execute it using the following command.  

ansible-playbook -i ../inventory/testinstance/ -l webserver playbook.yml --tags cloudwatch

So, the idea is I would execute it with the appserver host instead like this:

ansible-playbook -i ../inventory/testinstance/ -l appserver playbook.yml --tags cloudwatch

Think I can use the "when" statement to do this somehow?

Any help would be greatly received. Alternatively, is this approach just nonsense and there is a better way?

[Ompragash]

Hi Mark,

For your use-case, you can consider using Ansible magic variables https://docs.ansible.com/ansible/latest/user_guide/playbooks_variables.html#accessing-information-about-other-hosts-with-magic-variables

example:

when: inventory_hostname in groups ['webserver']

Regards,

Ompragash

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[Mark Farrington]

Thanks,   That did what I needed.

On Monday, June 15, 2020 at 11:18:56 AM UTC+1, Ompragash wrote:

Hi Mark,

For your use-case, you can consider using Ansible magic variables https://docs.ansible.com/ansible/latest/user_guide/playbooks_variables.html#accessing-information-about-other-hosts-with-magic-variables

example:

when: inventory_hostname in groups ['webserver']

Regards,

Ompragash

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[Dick Visser]

Hi

Another option is to have the content of that json config file stored
as a variable in group_vars. You can then just use a single task, and
limit the deployment to webservers or appservers. The config itself
will be YAML, which is slightly easier to read.
How feasible this is depends a bit on how complex that json data
structure is. Do you have an example of that template?

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[Mark Farrington]

Many thanks for the alternative.   I'm editing an existing project that is already set up this way and I think the config file is sufficiently different enough to justify the use of the template files so I'll go with the magic variables suggestion.    

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