2019-02-05 Ansible

Ansible Playbooks Beyond The Basics

Ansible Playbooks: Beyond the Basics#

Using Handlers#

handlers:
    - name: restart apache
      service: name=apache2 state=restarted

tasks:
    - name: Enable Apacherewrite module
      apache2_module: name=rewrite state=present
      notify: restart apache

Notify Multiple Handlers#

name: Rebuild application configuration. command: /opt/app/rebuild.sh notify:
- restart apache
- restart memcached

Have one Notifier Notify Another#

handlers: - name: restart apache service: name=apache2 state=restarted notify: restart memcached

  - name: restart memcached
    service: name=memcached state=restarted

Considerations#

Skipped Tasks do not run Handlers
Handlers run once, and only once, at the end of a play.
If a play fails before handlers ate notified, the handlers will never run.

Environment Variables#

Adding line to remote user account in .bash_profile:

name: Add an environment variable to the remote user’s shell. lineinfile: dest=~/.bash_profile regexp=^ENV_VAR= line=ENV_VAR=value

Only available to the shell command

Using the `register`#

name: Add an environment variable to the remote user’s shell. lineinfile: dest=~/.bash_profile regexp=^ENV_VAR= line=ENV_VAR=value
name: Get the value of the environment variable we just added. shell: ‘source ~/.bash_profile && echo $ENV_VAR’ register: foo
name: Print the value of the environment variable. debug: msg=”The variable is {{ foo.stdout }}”

Adding to Linux Environment Variables#

name: Add a global environment variable. lineinfile: dest=/etc/environment regexp=^ENV_VAR= line=ENV_VAR=value sudo: yes

Per Play Environment Variables#

Use the environment option for a file download url for example.

name: Download a file, using example-proxy as a proxy. get_url: url=http://www.example.com/file.tar.gz dest=~/Downloads/ environment: http_proxy: http://example-proxy:80/

That can become quite cumbersome so sometimes it is better to use a vars section

`vars` Section#

vars: var_proxy: http_proxy: http://example-proxy:80/ https_proxy: https://example-proxy:443/ [etc…] tasks: - name: Download a file, using example-proxy as a proxy. get_url: url=http://www.example.com/file.tar.gz dest=~/Downloads/ environment: var_proxy

Set a System wide Proxy (For Corporate Firewalls)#

in /etc/environment:

In the ‘vars’ section of the playbook (set to ‘absent’ to disable proxy):#

proxy_state: present # In the ‘tasks’ section of the playbook: - name: Configure the proxy. lineinfile: dest: /etc/environment regexp: “{{ item.regexp }}” line: “{{ item.line }}” state: “{{ proxy_state }}” with_items: - { regexp: “^http_proxy=”, line: “http_proxy=http://example-proxy:80/” } - { regexp: “^https_proxy=”, line: “https_proxy=https://example-proxy:443/” } - { regexp: “^ftp_proxy=”, line: “ftp_proxy=http://example-proxy:80/” }

# Testing a Remote Variable#

ansible test -m shell -a ‘echo $TEST’

Variables#

variables same as python but better to use just smalls and avoid numbers.

Assignments#

In an inventory file:

foo=bar

In a playbook:

foo: bar

Playbook Variables#

Passing in with command line:

ansible-playbook example.yml –extra-vars “foo=bar”

Pass in a json or yaml file:

-extra-vars “@even_more_vars.json”

In Playbook:

hosts: example vars: foo: bar tasks: # Prints “Variable ‘foo’ is set to bar”.
- debug: msg=”Variable ‘foo’ is set to {{ foo }}”

Or with a file vars_files:

# Main playbook file. - hosts: example vars_files: - vars.yml tasks: - debug: msg=”Variable ‘foo’ is set to {{ foo }}”

Variables in vars.yml:

---
# Variables file 'vars.yml' in the same folder as the playbook.
foo: bar

Conditionally importing a vars file#

Say you have centOS which uses httpd and debian that uses apache2:

apache_CentOS.yml

apache_-default.yml

---
  - hosts: example
    vars_files:
      - [ "apache_{{ ansible_os_family }}.yml", "apache_default.yml" ]
    tasks:
      - service: name={{ apache }} state=running

Inventory Variables#

Example of entire setting variables inline and for a group:

# Host-specific variables (defined inline). [washington] app1.example.com proxy_state=present app2.example.com proxy_state=absent # Variables defined for the entire group.

[washington:vars] cdn_host=washington.static.example.com api_version=3.0.1

# Best Practice#

Ansible’s documentation recommends not storing variables within the inventory. Instead, you can use group_vars and host_vars YAML variable files within a specific path, and Ansible will assign them to individual hosts and groups defined in your inventory

For a host app1.example.com, create:

/etc/ansible/host_vars/app1.example.com

and add variables as normal:

---
foo: bar
baz: qux

For a group of hosts, create:

/etc/ansible/group_vars/washington

# Magic Vars in Host and Group Vars#

If you ever need to retrieve a specific host’s variables from another host, Ansible provides a magic hostvars variable containing all the defined host variables.

# From any host, returns "jane".
{{ hostvars['host1']['admin_user'] }}

Registered Variables#

Ansible allows you to use register to store the output of a particular command in a variable at runtime

Eg.

- name: "Node: Check list of Node.js apps running."
  command: forever list
  register: forever_list
  changed_when: false

- name: "Node: Start example Node.js app."
  command: forever start {{ node_apps_location }}/app/app.js
  when: "forever_list.stdout.find('{{ node_apps_location}}/app/app.js') == -1"

Accessing Variables#

Simple variables (gathered by Ansible, defined in inventory files, or defined in playbook or variable files) can be used as part of a task using syntax like {{ variable }} .

- command: /opt/my-app/rebuild {{ my_environment }}

Lists#

A list is defined:

foo_list:
- one
- two
- three

Accessing the first element:

foo[0]      #python
foo|first   #jinja

Retrive info of large object#

To Retrieve info about eth0 network interface:

# In your playbook.
tasks:
  - debug: var=ansible_eth0

Knowing the structure of the variable you can now access elements:

{{ ansible_eth0.ipv4.address }}
{{ ansible_eth0['ipv4']['address'] }}

Facts - Variables derived from system information#

Get a list of Facts

ansible <host> -m setup

Variable Preference#

Command line always wins
Connection variables in the inventory file
Normal varialbles
Other Inventory Variables
Local facts with gather_facts
Role default variables defaults/maain.yml

roles should provide sane defaults playbooks should rarely define variables command line variables should be avoided where possible

Ansible Playbooks Beyond The Basics