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my inventory file's contents -
[webservers]
x.x.x.x ansible_ssh_user=ubuntu
[dbservers]
x.x.x.x ansible_ssh_user=ubuntu
in my tasks file which is in common role i.e. it will run on both hosts but I want to run a following task on host webservers not in dbservers which is defined in inventory file
- name: Install required packages
apt: name={{ item }} state=present
with_items:
- '{{ programs }}'
become: yes
tags: programs
is when module helpful or there is any other way? How could I do this ?
745
The easiest way to run only one task in Ansible Playbook is using the tags statement parameter of the “ansible-playbook” command. The default behavior is to execute all the tags in your Playbook with --tags all .
Ansible command limit option Using the --limit parameter of the ansible-playbook command is the easiest option to limit the execution of the code to only one host. The advantage is that you don't need to edit the Ansible Playbook code before executing to only one host.
Ansible delegate_to property or the keyword specified in the ansible-playbook is used to provide the control to run the task locally or to the other different hosts rather than running on the remote hosts specified on the inventory server list, and this can be the few tasks or running the entire play-book locally and ...
For such requirements where we need one tasks to run only once on a batch of hosts and we will be running that from Ansible controller node, we have feature parameter named run_once. When we have this parameter mentioned in a task, that task will run only once on first host it finds despite the host batch.
When you execute Ansible through an ad hoc command or by running a playbook, you must choose which managed nodes or groups you want to execute against. Patterns let you run commands and playbooks against specific hosts and/or groups in your inventory.
Ansible playbook will run only the task with the specified tag, it will skip the rest of the tasks in the playbook. Use the ‘–list-tags’ flag to view all the tags.
Task1: On the remote server named mwiapp01 defined under hostgroup named testserver this task would start a quick and simple web server using Netcat command and listen to port 8081. We have used async and poll of ansible to execute the job and run it background to know more about this refer to our previous article
An Ansible pattern can refer to a single host, an IP address, an inventory group, a set of groups, or all hosts in your inventory. Patterns are highly flexible - you can exclude or require subsets of hosts, use wildcards or regular expressions, and more. Ansible executes on all inventory hosts included in the pattern.
Thank you, this helps me too.
[production]
host1.dns.name
[internal]
host2.dns.name
- name: install the sphinx-search rpm from a remote repo on x86_64 - internal host
when: inventory_hostname in groups['internal']
yum:
name: http://sphinxsearch.com/files/sphinx-2.2.11-1.rhel7.x86_64.rpm
state: present
- name: install the sphinx-search rpm from a remote repo on i386 - Production
when: inventory_hostname in groups['production']
yum:
name: http://sphinxsearch.com/files/sphinx-2.2.11-2.rhel6.i386.rpm
state: present
If you want to run your role on all hosts but only a single task limited to the webservers group, then - like you already suggested - when is your friend.
You could define a condition like:
when: inventory_hostname in groups['webservers']
An alternative to consider in some scenarios is -
delegate_to: hostname
There is also this example form the ansible docs, to loop over a group. https://docs.ansible.com/ansible/latest/user_guide/playbooks_delegation.html -
- hosts: app_servers
tasks:
- name: gather facts from db servers
setup:
delegate_to: "{{item}}"
delegate_facts: True
loop: "{{groups['dbservers']}}"
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