Multiple expression RegEx in Ansible - ansible

Question

Note: I have next to zero experience with Ansible.
I need to be able to conditionally modify the configuration of a Kubernetes cluster control plane service. To do this I need to be able to find a specific piece of information in the file and if its value matches a specific pattern, change the value to something else.
To illustrate, consider the following YAML file:
apiVersion: v1
kind: Pod
metadata:
labels:
component: kube-controller-manager
tier: control-plane
name: kube-controller-manager
namespace: kube-system
spec:
containers:
- command:
- kube-controller-manager
- --authentication-kubeconfig=/etc/kubernetes/controller-manager.conf
- --authorization-kubeconfig=/etc/kubernetes/controller-manager.conf
- --bind-address=127.0.0.1
...
In this scenario, the line I'm interested in is the line containing --bind-address. If that field's value is "127.0.0.1", it needs to be changed to "0.0.0.0". If it's already "0.0.0.0", nothing needs to be done. (I could also approach it from the point of view of: if its not "0.0.0.0" then it needs to change to that.)
The initial thought that comes to mind is: just search for "--bind-address=127.0.0.1" and replace it with "--bind-address=0.0.0.0". Simple enough, eh? No, not that simple. What if, for some reason, there is another piece of configuration in this file that also matches that pattern? Which one is the right one?
The only way I can think of to ensure I find the right text to change, is a multiple expression RegEx match. Something along the lines of:
find spec:
if found, find containers: "within" or "under" spec:
if found, find - command: "within" or "under" containers: (Note: there can be more than one "command")
if found, find - kube-controller-manager "within" or "under" - command:
if found, find - --bind-address "within" or "under" - kube-controller-manager
if found, get the value after the =
if 127.0.0.1 change it to 0.0.0.0, otherwise do nothing
How could I write an Ansible playbook to perform these steps, in sequence and only if each step returns true?

Answer 1

Read the data from the file into a dictionary
- include_vars:
file: conf.yml
name: conf
gives
conf:
apiVersion: v1
kind: Pod
metadata:
labels:
component: kube-controller-manager
tier: control-plane
name: kube-controller-manager
namespace: kube-system
spec:
containers:
- command:
- kube-controller-manager
- --authentication-kubeconfig=/etc/kubernetes/controller-manager.conf
- --authorization-kubeconfig=/etc/kubernetes/controller-manager.conf
- --bind-address=127.0.0.1
Update the containers
- set_fact:
containers: []
- set_fact:
containers: "{{ containers +
(update_candidate is all)|ternary([_item], [item]) }}"
loop: "{{ conf.spec.containers|d([]) }}"
vars:
update_candidate:
- item is contains 'command'
- item.command is contains 'kube-controller-manager'
- item.command|select('match', '--bind-address')|length > 0
update: "{{ item.command|map('regex_replace',
'--bind-address=127.0.0.1',
'--bind-address=0.0.0.0') }}"
_item: "{{ item|combine({'command': update}) }}"
gives
containers:
- command:
- kube-controller-manager
- --authentication-kubeconfig=/etc/kubernetes/controller-manager.conf
- --authorization-kubeconfig=/etc/kubernetes/controller-manager.conf
- --bind-address=0.0.0.0
Update conf
conf_update: "{{ conf|combine({'spec': spec}) }}"
spec: "{{ conf.spec|combine({'containers': containers}) }}"
give
spec:
containers:
- command:
- kube-controller-manager
- --authentication-kubeconfig=/etc/kubernetes/controller-manager.conf
- --authorization-kubeconfig=/etc/kubernetes/controller-manager.conf
- --bind-address=0.0.0.0
conf_update:
apiVersion: v1
kind: Pod
metadata:
labels:
component: kube-controller-manager
tier: control-plane
name: kube-controller-manager
namespace: kube-system
spec:
containers:
- command:
- kube-controller-manager
- --authentication-kubeconfig=/etc/kubernetes/controller-manager.conf
- --authorization-kubeconfig=/etc/kubernetes/controller-manager.conf
- --bind-address=0.0.0.0
Write the update to the file
- copy:
dest: /tmp/conf.yml
content: |
{{ conf_update|to_nice_yaml(indent=2) }}
gives
shell> cat /tmp/conf.yml
apiVersion: v1
kind: Pod
metadata:
labels:
component: kube-controller-manager
tier: control-plane
name: kube-controller-manager
namespace: kube-system
spec:
containers:
- command:
- kube-controller-manager
- --authentication-kubeconfig=/etc/kubernetes/controller-manager.conf
- --authorization-kubeconfig=/etc/kubernetes/controller-manager.conf
- --bind-address=0.0.0.0
Example of a complete playbook for testing
- hosts: localhost
vars:
conf_update: "{{ conf|combine({'spec': spec}) }}"
spec: "{{ conf.spec|combine({'containers': containers}) }}"
tasks:
- include_vars:
file: conf.yml
name: conf
- debug:
var: conf
- set_fact:
containers: []
- set_fact:
containers: "{{ containers +
(update_candidate is all)|ternary([_item], [item]) }}"
loop: "{{ conf.spec.containers|d([]) }}"
vars:
update_candidate:
- item is contains 'command'
- item.command is contains 'kube-controller-manager'
- item.command|select('match', '--bind-address')|length > 0
update: "{{ item.command|map('regex_replace',
'--bind-address=127.0.0.1',
'--bind-address=0.0.0.0') }}"
_item: "{{ item|combine({'command': update}) }}"
- debug:
var: containers
- debug:
var: spec
- debug:
var: conf_update
- copy:
dest: /tmp/conf.yml
content: |
{{ conf_update|to_nice_yaml(indent=2) }}