Ansible Best Practices: The Essentials
THE ANSIBLE WAY
Principal 1
Complexity Kills Productivity
That's not just a marketing slogan. We really mean it and believe that. We strive to reduce complexity in how we've designed Ansible tools and encourage you to do the same.
Strive for simplification in what you automate.
Principal 2
Optimize For Readability
If done properly, it can be the documentation of your workflow automation.
Principal 3
Think Declaratively
Ansible is a desired state engine by design. If you're trying to "write code" in your plays and roles, you're setting yourself up for failure. Our YAML-based playbooks were never meant to be for programming.
Workflow
Treat your Ansible content like code
- Version control your Ansible content
- Start as simple as possible and iterate
- Start with a basic playbook and static inventory
- Refactor and modularize later
Workflow
Do it with Style
- Create a style guide for developers
- Consistency in:
- Tagging
- Whitespace
- Naming of Tasks, Plays, Variables, and Roles
- Directory Layouts
- Enforce the style
Project Layouts: Basic
The Ansible Way
basic-project
├── inventory
│ ├── group_vars
│ │ └── web.yml
│ ├── host_vars
│ │ └── db1.yml
│ └── hosts
└── site.yml
Project Layouts: Organizational Roles
myapp
├── roles
│ ├── myapp
│ │ ├── tasks
│ │ │ └── main.yml
│ │ └── ...
│ ├── nginx
│ │ └── ...
│ └── proxy
│ └── ...
└── site.yml
Project Layouts: Shared Roles
myapp/
├── config.yml
├── provision.yml
├── roles
│ └── requirements.yml
└── site.yml
Inventory
Give inventory nodes human-meaningful names rather than IPs or DNS hostnames.
Example 1
10.1.2.75
10.1.5.45
10.1.4.5
10.1.0.40
w14301.acme.com
w17802.acme.com
w19203.acme.com
w19304.acme.com
Example 2
Inventory
Group hosts for easier inventory selection and less conditional tasks -- the more groups the better.
What
[db]
db[1:4]
[web]
web[1:4]
db1 = db, east, dev
Where
[east]
db1
web1
db3
web3
[west]
db2
web2
db4
web4
When
[dev]
db1
web1
[test]
db3
web3
[prod]
db2
web2
db4
web4
Inventory
Use a single source of truth if you have it -- even if you have multiple sources, Ansible can unify them.
- Stay in sync automatically
- Reduce human error
Variables
Proper variable naming can make plays more readable and avoid variable name conflicts
- Use descriptive, unique human-meaningful variable names
- Prefix role variables with it’s "owner" such as a role name or package
apache_max_keepalive: 25
apache_port: 80
tomcat_port: 8080
Variables
Make the most of variables
- Find the appropriate place for your variables based on what, where and when they are set or modified
- Separate logic (tasks) from variables to reduce repetitive patterns and provided added flexibility.
Separate Logic From Variables
- name: Clone student lesson app for a user
host: nodes
tasks:
- name: Create ssh dir
file:
state: directory
path: /home/{{ username }}/.ssh
- name: Set Deployment Key
copy:
src: files/deploy_key
dest: /home/{{ username }}/.ssh/id_rsa
- name: Clone repo
git:
accept_hostkey: yes
clone: yes
dest: /home/{{ username }}/exampleapp
key_file: /home/{{ username }}/.ssh/id_rsa
repo: git@github.com:example/apprepo.git
Exhibit A
- Embedded parameter values and repetitive home directory value pattern in multiple places
- Works but could be more clearer and setup to be more flexible and maintainable
Separate Logic From Variables
- name: Clone student lesson app for a user
host: nodes
vars:
user_home_dir: "/home/{{ username }}"
user_ssh_dir: "{{ user_home_dir }}/.ssh"
deploy_key: "{{ user_ssh_dir }}/id_rsa"
app_dir: "{{ user_home_dir }}/exampleapp"
tasks:
- name: Create ssh dir
file:
state: directory
path: "{{ user_ssh_dir }}"
- name: Set Deployment Key
copy:
src: files/deploy_key
dest: "{{ deploy_key }}"
- name: Clone repo
git:
dest: "{{ app_dir }}"
key_file: "{{ deploy_key }}"
repo: git@github.com:example/exampleapp.git
accept_hostkey: yes
clone: yes
Exhibit B
- Parameters values are set thru values away from the task and can be overridden.
- Human meaningful variables "document" what’s getting plugged into a task parameter
- More easily refactored into a role
Plays & Tasks
Use native YAML syntax to maximize the readability of your plays
- Vertical reading is easier
- Supports complex parameter values
- Works better with editor syntax highlighting in editors
Use Native YAML Syntax
No!
- name: install telegraf
yum: name=telegraf-{{ telegraf_version }} state=present update_cache=yes disable_gpg_check=yes enablerepo=telegraf
notify: restart telegraf
- name: configure telegraf
template: src=telegraf.conf.j2 dest=/etc/telegraf/telegraf.conf
- name: start telegraf
service: name=telegraf state=started enabled=yes
Use Native YAML Syntax
Better, but no
- name: install telegraf
yum: >
name=telegraf-{{ telegraf_version }}
state=present
update_cache=yes
disable_gpg_check=yes
enablerepo=telegraf
notify: restart telegraf
- name: configure telegraf
template: src=telegraf.conf.j2 dest=/etc/telegraf/telegraf.conf
- name: start telegraf
service: name=telegraf state=started enabled=yes
Use Native YAML Syntax
Yes!
- name: install telegraf
yum:
name: telegraf-{{ telegraf_version }}
state: present
update_cache: yes
disable_gpg_check: yes
enablerepo: telegraf
notify: restart telegraf
- name: configure telegraf
template:
src: telegraf.conf.j2
dest: /etc/telegraf/telegraf.conf
notify: restart telegraf
- name: start telegraf
service:
name: telegraf
state: started
enabled: yes
Plays & Tasks
Names improve readability and user feedback
- Give all your playbooks, tasks and blocks brief, reasonably unique and human-meaningful names
Plays & Tasks
Exhibit A
- hosts: web
tasks:
- yum:
name: httpd
state: latest
- service:
name: httpd
state: started
enabled: yes
PLAY [web]
********************************
TASK [setup]
********************************
ok: [web1]
TASK [yum]
********************************
ok: [web1]
TASK [service]
********************************
ok: [web1]
Plays & Tasks
Exhibit B
- hosts: web
name: installs and starts apache
tasks:
- name: install apache packages
yum:
name: httpd
state: latest
- name: starts apache service
service:
name: httpd
state: started
enabled: yes
PLAY [install and starts apache]
********************************
TASK [setup]
********************************
ok: [web1]
TASK [install apache packages]
********************************
ok: [web1]
TASK [starts apache service]
********************************
ok: [web1]
Plays & Tasks
Focus avoids complexity
- Keep plays and playbooks focused. Multiple simple ones are better than having a huge single playbook full of conditionals.
- Follow the Linux principle of do one thing, and one thing well
Plays & Tasks
Clean up your debugging tasks
- Make them optional with the verbosity parameter so they’re only displayed when they are wanted.
- debug:
msg: "This always displays"
- debug:
msg: "This only displays with ansible-playbook -vv+"
verbosity: 2
Plays & Tasks
Don’t just start services -- use smoke tests
- name: check for proper response
uri:
url: http://localhost/myapp
return_content: yes
register: result
until: '"Hello World" in result.content'
retries: 10
delay: 1
Plays & Tasks
Use run commands sparingly
- Use the run command modules like shell and command as a last resort
- The command module is generally safer
- The shell module should only be used for I/O redirect
Plays & Tasks
Always seek out a module first
- name: add user
command: useradd appuser
- name: install apache
command: yum install httpd
- name: start apache
shell: |
service httpd start && chkconfig httpd on
- name: add user
user:
name: appuser
state: present
- name: install apache
yum:
name: httpd
state: latest
- name: start apache
service:
name: httpd
state: started
enabled: yes
Plays & Tasks
Still using run commands a lot?
- hosts: all
vars:
cert_store: /etc/mycerts
cert_name: my cert
tasks:
- name: check cert
shell: certify --list --name={{ cert_name }} --cert_store={{ cert_store }} | grep "{{ cert_name }}"
register: output
- name: create cert
command: certify --create --user=chris --name={{ cert_name }} --cert_store={{ cert_store }}
when: output.stdout.find(cert_name)" != -1
register: output
- name: sign cert
command: certify --sign --name={{ cert_name }} --cert_store={{ cert_store }}
when: output.stdout.find("created")" != -1
Plays & Tasks
Develop your own module
- hosts: all
vars:
cert_store: /etc/mycerts
cert_name: my cert
tasks:
- name: create and sign cert
certify:
state: present
sign: yes
user: chris
name: "{{ cert_name }}"
cert_store: "{{ cert_store }}"
Plays & Tasks
Separate provisioning from deployment and configuration tasks
acme_corp/
├── configure.yml
├── provision.yml
└── site.yml
$ cat site.yml
---
- include: provision.yml
- include: configure.yml
Templates
Jinja2 is powerful but you needn't use all of it
Templates should be simple:
- Variable substitution
- Conditionals
- Simple control structures/iterations
- Design your templates for your use case, not the world's
Things to avoid:
- Anything that can be done directly in Ansible
- Managing variables in a template
- Extensive and intricate conditionals
- Conditional logic based on embedded hostnames
- Complex nested iterations
Templates
Identify generated files
- Label template output files as being generated by Ansible
- Consider using the ansible_managed variable with the comment filter
- Especially important when you are starting out and not everything is Ansible managed
{{ ansible_managed | comment }}
Roles
- Like playbooks -- keep roles purpose and function focused
- Use a roles/ subdirectory for roles developed for organizational clarity in a single project
- Follow the Ansible Galaxy pattern for roles that are to be shared beyond a single project
- Limit role dependencies
Roles
- Use ansible-galaxy init to start your roles...
- ...then remove unneeded directories and stub files
- Use ansible-galaxy to install your roles -- even private ones
- Use a roles files (i.e. requirements.yml) to manifest any external roles your project is using
- Always peg a role to a specific version such as a tag or commit
Scaling Your Ansible Workflow
Command line tools have their limitations
- Coordination across distributed teams & organizations...
- Controlling access to credentials...
- Track, audit and report automation and management activity...
- Provide self-service or delegation...
- Integrate automation with enterprise systems...
Recap
- Complexity Kills Productivity
- Optimize For Readability
- Think Declaratively
Thank You!
- Complexity Kills Productivity
- Optimize For Readability
- Think Declaratively
