Ansible
From www.ansible.com:
- Ansible is a radically simple IT automation engine that automates cloud provisioning, configuration management, application deployment, intra-service orchestration, and many other IT needs.
Installation
On the control machine (master), install the ansible-core package. Additionally, you can install the ansible package, which provides a range of community curated collections.
On the managed machines (nodes), where you want to automate deployment or configuration tasks, python is required and it may be necessary to indicate the specific #Python binary location in some circumstances. A way to communicate with the node is also necessary, this is usually SSH. Note that a functioning SSH key setup eases the use of Ansible but is not required.
Basic usage
Configuration
Ansible parameters are set in the configuration file which can either be ansible.cfg in the current directory, .ansible.cfg in the home directory or /etc/ansible/ansible.cfg, whichever it finds first.
A base config can be generated with:
$ ansible-config init --disabled > ansible.cfg
Inventory
The infrastructure is listed in the Ansible inventory file, which defaults to being saved in the location /etc/ansible/hosts or one can specify a different inventory file using the -i command line switch. For instance, the following inventory defines a cluster with 7 nodes organized into two groups:
/etc/ansible/hosts
[control] 192.168.12.1 foo-[a:c].example.org localhost ansible_connection=local [managed] 192.168.12.2 192.168.12.3
One can assign specific attributes to every node in the infrastructure file at the corresponding line or in the ansible.cfg configuration file.
By default Ansible executes playbooks over SSH, the ansible_connection parameter extends the connection to:
-
localto deploy the playbook to the control machine itself -
dockerdeploys the playbook directly into Docker containers
Check Ansible - intro inventory for details.
Ping
You may check if all the nodes listed in the inventory are alive by
$ ansible all -m ping
Playbook
Playbooks are the main organizational unit to configure and deploy the whole infrastructure. Check the official document for more details. Here is an extremely simple demonstration, where the administrator of the above inventory wants to perform a full system upgrade on a set of Arch Linux hosts. First, create a playbook file, with YAML formatting (always 2 spaces indentation):
syu.yml
---
- name: All hosts up-to-date
hosts: control managed
become: true
tasks:
- name: Full system upgrade
community.general.pacman:
update_cache: true
upgrade: true
Then, run the playbook script:
$ ansible-playbook --ask-become-pass syu.yml
Vault
A vault can be used to keep sensitive data in an encrypted form in playbooks or roles, rather than in plaintext. The vault password can be stored in plaintext in a file, for example vault_pass.txt containing myvaultpassword, to be used later on as a command parameter:
$ ansible-playbook site.yml --vault-id vault_pass.txt
In order to encrypt the content the var content of a variable named varname using the password stored in vault_pass.txt, the following command should be used:
$ ansible-vault encrypt_string --vault-id vault_pass.txt 'the var content' --name varname
More securely, to avoid inputting the variable content in the command line and be prompted for it instead, one can use:
$ ansible-vault encrypt_string --vault-id vault_pass.txt --stdin-name varname
Reading plaintext input from stdin. (ctrl-d to end input)
The command returns directly the protected variable that can be inserted into a playbook. Encrypted and non-encrypted variables can coexist in a YAML file as illustrated below:
notsecret: myvalue
mysecret: !vault |
$ANSIBLE_VAULT;1.1;AES256
66386439653236336462626566653063336164663966303231363934653561363964363833313662
6431626536303530376336343832656537303632313433360a626438346336353331386135323734
62656361653630373231613662633962316233633936396165386439616533353965373339616234
3430613539666330390a313736323265656432366236633330313963326365653937323833366536
3462
other_not_secret: othervalue
Package management
Official repositories
Ansible has a pacman module (provided by the ansible package) to handle installation, removal and system upgrades with pacman.
AUR
For the Arch User Repository (AUR), it is required to use the external module ansible-aur. See the README for use and installation instructions.
While Ansible expects to ssh as root, AUR helpers do not allow executing operations as root, they all fail with "you cannot perform this operation as root". For Ansible automation, it is therefore recommended to create a user, for example named aur_builder, that has no need for password with pacman in sudoers. This can be done in Ansible with the following actions:
task.yml
- user: name=aur_builder
- lineinfile:
path: /etc/sudoers.d/aur_builder-allow-to-sudo-pacman
state: present
line: "aur_builder ALL=(ALL) NOPASSWD: /usr/bin/pacman"
validate: /usr/sbin/visudo -cf %s
create: yes
Then, AUR helpers or makepkg can be used associated with the Ansible parameters become: yes and become_user: aur_builder
Tips and tricks
User account creation
Ansible can manage user accounts and in particular it is able to create new ones. This is achieved in playbooks with the user module which takes an optional password argument to set the user's password. It is the hashed value of the password that needs to be provided to the module.
The hashing can simply be performed on the fly within Ansible using one of its internal hash-filters:
- user:
name: user_name
password: "{{ 'user_password' | password_hash('sha512', 'mypermsalt') }}"
shell: /usr/bin/nologin
With this approach it is recommended to vault-encrypt user_password so that it does not appear in plain text, see #Vault. However, an encrypted variable cannot be piped directly and will first need to be assigned to another one that will be piped.
Alternatively, the hashing can be performed outside Ansible. The following commands return respectively the MD5 and the SHA512 hashed values of user_password:
$ openssl passwd -1 user_password
$ python -c 'import crypt; print(crypt.crypt("user_password", crypt.mksalt(crypt.METHOD_SHA512)))'
Python binary location
Ansible requires Python on the target machine. By default Ansible assumes it can find a /usr/bin/python on the remote system that is a 2.X or 3.X version, specifically 2.6 or higher.
If some of your modules specifically require Python2, you need to inform Ansible about its location by setting the ansible_python_interpreter variable in the inventory file. This can be done by using host groups in the inventory:
/etc/ansible/hosts
[archlinux] server1 server2 [debian] server3 [archlinux:vars] ansible_python_interpreter=/usr/bin/python2
More information about Python version support in Ansible is available in [1], [2] and [3].
Troubleshooting
Unarchive
The unarchive module unpacks an archive. However tar files are not well supported and several outstanding issues are reported in GitHub - unarchive. In particular when the parameter keep_newer is set to yes, idempotence is not observed. In case you face an issue with the module, you can use instead the zip format which is better integrated in Ansible.
See also
- https://www.ansible.com/resources/videos/quick-start-video - Ansible concept in 12 minutes
- https://docs.ansible.com/ansible/latest/collections/community/general/pacman_module.html - Official documentation of the pacman module