Execute multiple Ansible tasks once per group and use a dedicated variable to store custom data.
Define hosts that will contain multiple application clusters.
$ cat hosts
[application:children] application_cluster_development application_cluster_production [application_cluster_development] dev_server_1 ansible_host=127.0.0.1 dev_server_2 ansible_host=127.0.0.1 dev_server_3 ansible_host=127.0.0.1 [application_cluster_production] prod_server1 ansible_host=127.0.0.1 prod_server2 ansible_host=127.0.0.1 prod_server3 ansible_host=127.0.0.1
Define per cluster configuration.
$ cat group_vars/application_cluster_production/application_cluster.yml
---
cluster_items:
- name: Alpha
state: present
- name: Beta
state: present
- name: Gamma
state: present
- name: Delta
state: present
- name: Epsilon
state: absent
Define Ansible playbook.
$ cat playbook.yml
---
- hosts: application
tasks:
- name: Determine application cluster group
set_fact:
application_cluster_group: '{{ group_names | select("match","application_cluster_*") | first }}'
- block:
- name: Define per cluster variable # per cluster short-lived variable
set_fact:
per_cluster_variable: '{{ per_cluster_variable | default({}) |
combine({inventory_hostname: {
"cluster_items": cluster_items|default([]),
"cluster_group": application_cluster_group,
"cluster_group_members": groups[application_cluster_group]},
"cluster_hostname": inventory_hostname
})
}}'
- name: Display per cluster variable
debug:
var: per_cluster_variable[inventory_hostname]
- name: List cluster items that should exist
debug:
var: item
loop: '{{ per_cluster_variable[inventory_hostname]["cluster_items"] }}'
when:
- item.state == "present"
- name: List cluster items that should not exist
debug:
var: item
loop: '{{ per_cluster_variable[inventory_hostname]["cluster_items"] }}'
when:
- item.state == "absent"
when: inventory_hostname == groups[application_cluster_group][0] # execute this block once per group
Execute created playbook to see how it works.
$ ansible-playbook -i hosts playbook.yml
PLAY [application] *********************************************************************************************************************************************
TASK [Gathering Facts] *****************************************************************************************************************************************
ok: [prod_server2]
ok: [dev_server_2]
ok: [dev_server_3]
ok: [prod_server1]
ok: [dev_server_1]
ok: [prod_server3]
TASK [Determine application cluster group] *********************************************************************************************************************
ok: [dev_server_1]
ok: [dev_server_2]
ok: [dev_server_3]
ok: [prod_server1]
ok: [prod_server2]
ok: [prod_server3]
TASK [Define per cluster variable] *****************************************************************************************************************************
ok: [dev_server_1]
skipping: [dev_server_2]
skipping: [dev_server_3]
ok: [prod_server1]
skipping: [prod_server2]
skipping: [prod_server3]
TASK [Display per cluster variable] ****************************************************************************************************************************
ok: [dev_server_1] => {
"per_cluster_variable[inventory_hostname]": {
"cluster_group": "application_cluster_development",
"cluster_group_members": [
"dev_server_1",
"dev_server_2",
"dev_server_3"
],
"cluster_items": []
}
}
skipping: [dev_server_2]
skipping: [dev_server_3]
ok: [prod_server1] => {
"per_cluster_variable[inventory_hostname]": {
"cluster_group": "application_cluster_production",
"cluster_group_members": [
"prod_server1",
"prod_server2",
"prod_server3"
],
"cluster_items": [
{
"name": "Alpha",
"state": "present"
},
{
"name": "Beta",
"state": "present"
},
{
"name": "Gamma",
"state": "present"
},
{
"name": "Delta",
"state": "present"
},
{
"name": "Epsilon",
"state": "absent"
}
]
}
}
skipping: [prod_server2]
skipping: [prod_server3]
TASK [List cluster items that should exist] ********************************************************************************************************************
skipping: [dev_server_2]
skipping: [dev_server_3]
ok: [prod_server1] => (item={'name': 'Alpha', 'state': 'present'}) => {
"ansible_loop_var": "item",
"item": {
"name": "Alpha",
"state": "present"
}
}
skipping: [prod_server2]
ok: [prod_server1] => (item={'name': 'Beta', 'state': 'present'}) => {
"ansible_loop_var": "item",
"item": {
"name": "Beta",
"state": "present"
}
}
ok: [prod_server1] => (item={'name': 'Gamma', 'state': 'present'}) => {
"ansible_loop_var": "item",
"item": {
"name": "Gamma",
"state": "present"
}
}
ok: [prod_server1] => (item={'name': 'Delta', 'state': 'present'}) => {
"ansible_loop_var": "item",
"item": {
"name": "Delta",
"state": "present"
}
}
skipping: [prod_server3]
skipping: [prod_server1] => (item={'name': 'Epsilon', 'state': 'absent'})
TASK [List cluster items that should not exist] ****************************************************************************************************************
skipping: [dev_server_2]
skipping: [dev_server_3]
skipping: [prod_server2]
skipping: [prod_server1] => (item={'name': 'Alpha', 'state': 'present'})
skipping: [prod_server1] => (item={'name': 'Beta', 'state': 'present'})
skipping: [prod_server1] => (item={'name': 'Gamma', 'state': 'present'})
skipping: [prod_server1] => (item={'name': 'Delta', 'state': 'present'})
ok: [prod_server1] => (item={'name': 'Epsilon', 'state': 'absent'}) => {
"ansible_loop_var": "item",
"item": {
"name": "Epsilon",
"state": "absent"
}
}
skipping: [prod_server3]
PLAY RECAP *****************************************************************************************************************************************************
dev_server_1 : ok=4 changed=0 unreachable=0 failed=0 skipped=2 rescued=0 ignored=0
dev_server_2 : ok=2 changed=0 unreachable=0 failed=0 skipped=4 rescued=0 ignored=0
dev_server_3 : ok=2 changed=0 unreachable=0 failed=0 skipped=4 rescued=0 ignored=0
prod_server1 : ok=6 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
prod_server2 : ok=2 changed=0 unreachable=0 failed=0 skipped=4 rescued=0 ignored=0
prod_server3 : ok=2 changed=0 unreachable=0 failed=0 skipped=4 rescued=0 ignored=0
Additional notes
I keep things simpler then presented in the above example, as a basic list accessed using per_cluster_variable[inventory_hostname] variable is more then enough.
per_cluster_variable: '{{ per_cluster_variable | default({}) | combine({inventory_hostname: cluster_items|default([]) }) }}'
This technique is very useful when you use Ansible to provision multiple clusters, for example, to keep an index list for Elasticsearch or a topic list for Kafka, …