Ansible and Python are just, like, made for each other, man. Feel the love.

1. Ansible Python
Greg DeKoenigsberg
Director, Ansible Community, Red Hat
@gregdek

2. Q+A
“Why are you starting with Q+A?”

3. What is Ansible, anyway?
“Isn’t it just distributed ssh?”

4. “Well, yes. Basically.”

5. “But it’s a lot more than that, too.”

6. Ansible is:
Distributed ssh
Plus a simple definition language
Plus hundreds of modules

7. Here’s a simple Ansible inventory.

8. mail.example.com
[webservers]
foo.example.com
bar.example.com
www[01:50].example.com
[dbservers]
db[a:f].example.com
[webservers:vars]
proxy=proxy.example.com

9. Here are some simple Ansible commands.

10. $ ansible webservers -a "/sbin/reboot"

11. $ ansible webservers -m command -a "/sbin/reboot"

12. $ ansible webservers -m command -a "/sbin/reboot" -f 10

13. Here’s a simple Ansible playbook.

14. ---
- hosts: webservers
remote_user: root
tasks:
- name: ensure apache is at the latest version
yum: name=httpd state=latest
- name: write the apache config file
template: src=/srv/httpd.j2 dest=/etc/httpd.conf
- hosts: databases
remote_user: root
tasks:
- name: ensure postgresql is at the latest version
yum: name=postgresql state=latest
- name: ensure that postgresql is started
service: name=postgresql state=started

15. So what is Ansible actually doing?
● Connects to the target systems simultaneously
○ One ssh connection per host, up to fork limit
● Copies over Ansible and all necessary module code
● Runs setup.py to assess the system state
● Runs through each individual play
○ Plays invoke module code, which is (almost always) Python
○ Runs in parallel by default, one play at a time over all systems
● Does things, or not
● Gathers output and sends back over ssh
● Removes itself when it’s finished!
○ (which is why we call Ansible “agentless”)

16. Oh btw, “state” is kind of a big deal in
configuration management tools.

17. Old school sysadmin tool: bash
“Here’s a list of commands. Do exactly what I tell you to do.”

18. New school sysadmin tool: ansible
“Here’s a description of a desired system state. Do as little as
possible to ensure that the system is in that state.”
(The cool kids call this “idempotence”, but no one seems to
agree on how to pronounce that word.)

19. You can’t set a system to a desired state without knowing the
system’s current state.
That’s why Ansible does “fact gathering” before every run,
using the “setup” module.
Modules can look at facts, and they can also talk to the target
host directly, to figure out state before taking action.

20. Here’s a simple Ansible module.
$ cat cloud/atomic/atomic_host.py

21. 1 #!/usr/bin/python
2 # -*- coding: utf-8 -*-
3
4 # This file is part of Ansible
5 #
6 # Ansible is free software: you can redistribute it and/or modify
7 # it under the terms of the GNU General Public License as published by
8 # the Free Software Foundation, either version 3 of the License, or
9 # (at your option) any later version.
10 #
11 # Ansible is distributed in the hope that it will be useful,
12 # but WITHOUT ANY WARRANTY; without even the implied warranty of
13 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 # GNU General Public License for more details.
15 #
16 # You should have received a copy of the GNU General Public licenses
17 # along with Ansible. If not, see <http://www.gnu.org/licenses/>.
18
19 ANSIBLE_METADATA = {'status': ['preview'],
20 'supported_by': 'community',
21 'version': '1.0'}

22. 23 DOCUMENTATION='''
24 ---
25 module: atomic_host
26 short_description: Manage the atomic host platform
27 description:
28 - Manage the atomic host platform
29 - Rebooting of Atomic host platform should be done outside this module
30 version_added: "2.2"
31 author: "Saravanan KR @krsacme"
32 notes:
33 - Host should be an atomic platform (verified by existence of '/run/ostree-booted'
file)
34 requirements:
35 - atomic
36 - "python >= 2.6"
37 options:
38 revision:
39 description:
40 - The version number of the atomic host to be deployed. Providing
C(latest) will upgrade to the latest available version.
41 required: false
42 default: latest
43 aliases: ["version"]
44 '''

23. 46 EXAMPLES = '''
47
48 # Upgrade the atomic host platform to the latest version (atomic host
upgrade)
49 - atomic_host:
50 revision: latest
51
52 # Deploy a specific revision as the atomic host (atomic host deploy
23.130)
53 - atomic_host:
54 revision: 23.130
55 '''
56
57 RETURN = '''
58 msg:
59 description: The command standard output
60 returned: always
61 type: string
62 sample: 'Already on latest'
63 '''

24. 65 def core(module):
66 revision = module.params['revision']
67 args = []
68
69 module.run_command_environ_update = dict(LANG='C', LC_ALL='C', LC_MESSA
GES='C')
70
71 if revision == 'latest':
72 args = ['atomic', 'host', 'upgrade']
73 else:
74 args = ['atomic', 'host', 'deploy', revision]
75
76 out = {}
77 err = {}
78 rc = 0
79
80 rc, out, err = module.run_command(args, check_rc=False)
81
82 if rc == 77 and revision == 'latest':
83 module.exit_json(msg="Already on latest", changed=False)
84 elif rc != 0:
85 module.fail_json(rc=rc, msg=err)
86 else:
87 module.exit_json(msg=out, changed=True)

25. 90 def main():
91 module = AnsibleModule(
92 argument_spec = dict(
93 revision = dict(default='latest', required=False, aliases=["version"]),
94 ),
95 )
96
97 # Verify that the platform is atomic host
98 if not os.path.exists("/run/ostree-booted"):
99 module.fail_json(msg="Module atomic_host is applicable for Atomic Host
Platforms only")
100
101 try:
102 core(module)
103 except Exception as e:
104 module.fail_json(msg=str(e))
105
106
107 # import module snippets
108 from ansible.module_utils.basic import *
109 if __name__ == '__main__':
110 main()

26. Ansible is “kind of a big deal” in Python-land
As in, it’s the largest project in contributors on GitHub.
By a lot.
As of 2/22/17, Ansible has 2,549 contributors.

27. Why does Ansible have so many contributors?
● Because the architecture is highly modular
● Because there are lots of examples to cargo cult
● Because the docs and guidelines are “good enough”
● Because GitHub provides common participatory infrastructure
● Because Python is an awesome language that’s easy to learn
● Because our community matters to us

28. Join the Ansible Philadelphia meetup!
Kickoff meeting, Thursday March 23rd:
https://www.meetup.com/Ansible-Philadelphia/

29. Thanks! / Q+A again / Story Time
@gregdek
greg@ansible.com