Ansible

Ansible is an open source configuration management tool written in Python and helps automate software configuration and deployment. It manages remote hosts via SSH or PowerShell and requires no agents on the client side. Changes can be executed on one or more hosts which can be on different networks, so long as it is accessible by the Ansible host.

Introduction[edit | edit source]

Ansible provides a bunch of modules that perform a certain action. For example, the package module installs a package on the host machine. Each module can take any number of parameters which are specified by a task definition. We could define a new task that passes 'vim' as a parameter to the package module so that vim gets installed. A set of roles that together implements a specific feature or sets up the 'role' of a machine can be bundled together as an Ansible role. A playbook specifies which host or host groups implement which roles.

In summary:

Inventory: file or script that tells Ansible what the hosts are. Hosts can be bundled together into groups. Groups can inherit other groups.
Playbook: A playbook tells Ansible what tasks or roles a host or host group need to implement
Role: A bundle of tasks, files, and templates that configures a specific feature or role.
Task: A list of parameters which are called against a specific Module in order to do a specific action
Module: A piece of code which does an action

Modules & Tasks[edit | edit source]

Modules can take in any number of parameters as variables. Modules can also return data back to Ansible which can be used later on by other modules. A module by itself isn't able to do anything and can only 'run' when used as a task. A Task is simply a list item that specifies a module and its parameters.

A single module can be executed via the ansible command while multiple modules can be executed through the use of a playbook which describes the list of tasks or a bundle of tasks (called roles) it needs to perform.

Ansible uses the Jinja2 template engine and all parameters that are passed to Ansible can be templated. Uses of this are found throughout the examples below and allows for the use of loops (by iterating over lists) and embedding variables within strings. Templated values must be enclosed in double quotes.

Modules which are commonly used and their commonly used parameters are listed below:

Module	parameter	Description
yum/dnf	- name: Install NTP yum: name: ntp state: present - name: Install common packages dnf: name: - git - vim - zsh	Installs a package. You may also use loops to call the module multiple times for each item. Eg: - name: Install packages dnf: name: "{{ item }}" with_items: - git - vim This is something which isn't required for the yum/dnf modules since version 2.0.
package	- name: Ensure NFS utils are installed package: name: "{{ __packages.client }}" state: "{{ 'latest' if upgrade else 'present' }}"	This module will use the proper underlying package manager suitable on the system, making cross-platform tasks easier to write. The name parameter also accepts a list, like yum/dnf.
template	- name: Configure NTP notify: restart ntp template: src: ntp.conf.j2 dest: /etc/ntp.conf	Copy a templated file. Notice that we also call 'restart ntp' when the file is changed. 'restart ntp' is a task defined under the `handlers/main.yml` file. Template may include variables passed to this playbook.
service	- name: Start the ntp service service: name: ntpd state: started enabled: yes - name: restart ntp service: name: ntpd state: restarted	Ensures something is started and enabled on startup
debug	- name: "testing something" debug: msg: "item: {{ item }}" with_items: - 1 - 2	Debug messages
command	- name: Extract archive command: /bin/tar xvf wordpress.tar.gz args: chdir: /srv/ creates: /srv/wordpress - name: safely use templated variable to run command command: cat {{ myfile\|quote }} register: myoutput	Runs a command
shell	- name: Shell command shell: "echo $HOME \| grep something"	Similar to command, but the task is executed inside a shell. Environment variables and piping will work as a result. The `creates` argument can be used so that the command only runs when the file does not exist.
copy	- name: Copy using inline content copy: content: \| this is some file content of mine. dest: /tmp/file - name: Copy a "sudoers" file on the remote machine for editing copy: src: /etc/sudoers dest: /etc/sudoers.edit remote_src: yes validate: /usr/sbin/visudo -csf %s	Copies files or sets file contents
file	- name: Create MariaDB log file file: path: /var/log/mysqld.log state: touch owner: mysql group: mysql mode: 0775 - name: Create MariaDB PID directory file: path: /var/run/mysqld state: directory owner: mysql group: mysql mode: 0775	Creates a file or directory
stat	- name: Check that the somefile.conf exists stat: path: /etc/file.txt register: stat_result changed_when: False - name: Create the file, if it doesnt exist already file: path: /etc/file.txt state: touch when: not stat_result.stat.exists	Stats a file, which can be used to only run something based on a file's existence.
find	- name: Find files with globbing find: paths: /tmp patterns: "*.swp" register: list_of_files ## Loop over list_of_files using with_items. - name: Do something with file list file: path: "{{ item.path }}" state: absent with_items: "{{ list_of_files.files }}"	finds files by name or by pattern.
mount	- name: Mount /home mount: fstype: nfs opts: "vers=3,intr,hard" path: /home src: "netapp{{ fileserver_index }}:/ArcHome" state: present	Mounts a filesystem
firewalld	- name: insert firewalld rule firewalld: port: {{ mysql_port }}/tcp permanent: true state: enabled immediate: yes	Manages the firewall
git	- name: Copy the code from repository git: repo: {{ repository }} dest: /var/www/html/	You can clone an entire git repository to some location.
systemd	- name: Make sure a service is running systemd: state: started name: httpd - name: Enable a timer for dnf-automatic systemd: name: dnf-automatic.timer state: started enabled: yes	Manages systemd services and timers. State must be one of: reloaded restarted started stopped
user	- title: Create a new user user: name: remote shell: /bin/bash groups: admin,wheel append: yes
group	- title: Create a new group group: name: remote state: present
authorized_key	- name: Set an authorized key authorized_key: user: remote state: present key: "{{ lookup('file', '/home/remote/.ssh/id_rsa.pub') }}"	The key can also be specified as just a string.

Roles[edit | edit source]

Roles define a set of tasks that should be done. I like to think of Roles as a bundle or grouping of tasks. Ansible Galaxy contains a bunch of other roles that can be used. GitHub also has lots of other roles users have made public which may do what you want.

Roles help organize tasks into a single unit. For example, you may want to create a webserver role that contains instructions on setting up Apache and another database role with instructions on setting up MySQL. Creating a new role involves creating the following directory structure:

roles/
   installapache/
     tasks/
     handlers/
     templates/
     vars/
     defaults/
   installtomcat/
     tasks/
     meta/

Each role should be its own subdirectory in the roles directory. Each role should also have folders for each of: tasks for all ansible tasks the role should perform, handlers containing all handlers in this role, files for files needed by the role, such as configuration files, templates containing templating data, vars containing values that override defaults set in the defaults directory, meta for any metadata needed for this role, such as dependency data. In each of these directories, the main.yml file will be read and used if it exists.

In the example above, we have a installapache role and installtomcat role.

Inside installapache/tasks/main.yml, we can load the appropriate set of tasks depending on the distribution:

- name: import a tasks based on OS platform 
  import_tasks: centos.yml 
  when: ansible_distribution == 'CentOS' 
- import_tasks: ubuntu.yml 
  when: ansible_distribution == 'Ubuntu'

We would then create a centos.yml and ubuntu.yml within this same tasks directory with all the tasks that should be done in this role. Eg.

---
- name: Install Apache using yum
  yum:
    name: "httpd"
    state: latest
- name: Start the Apache server
  service:
    name: httpd
    state: started

As Dependencies[edit | edit source]

Roles can be included as dependencies. Under meta, define something like:

dependencies:
  - role: common
    vars:
      some_parameter: 3
  - role: apache
    vars:
      apache_port: 80
  - role: postgres
    vars:
      dbname: blarg
      other_parameter: 12

Inventory[edit | edit source]

An Inventory contains a list of hosts managed by Ansible. It outlines any groups and their relationship with hosts. This file can be written in either INI or YAML. By default, the inventory file is loaded from /etc/ansible/hosts, but can be specified with -i when calling ansible or ansible-playbook.

An example INI inventory file is shown below. Note that groups are defined as named INI sections. Group inheritance and variables are specified with the :children and :vars in the INI section.

[webservers]
web1.example.com ansible_user=bob
web2.example.com ansible_host=192.168.81.142 ansible_port=3333

; variables that apply only to the webservers group
[webservers:vars]
listen_port=8080

[apservers]
ap1.example.com
ap2.example.com

[dbservers]
; db01, db02, ..., db10
db[01:10].example.com

; servers group contains the following sub-groups
[servers:children]
webservers
apservers
dbservers

Here, we have four distinct groups: webservers, apservers, dbservers, and servers. The servers group includes every host that's defined here since it includes all the other groups as its children. Additionally, there is a built-in group named all which can be used.

Host ranges can be specified with brackets, such as [01:10] to denote nodes from 01 (with a leading 0) through 10.

Variable overrides[edit | edit source]

You can override specific variables in the inventory file. In the example above, the web servers have their user, host, and ports overridden so that Ansible will connect to these hosts using the specified host and ports. Other variables that you might be interested are:

Description	Variables
Override the host's address. Connect to this address rather than the relying on the hostname.	`ansible_host=10.1.2.6`
Override the default SSH port	`ansible_port=2222`
SSH as this user when connecting to the host (rather than root)	`ansible_user=opc`
Use this identity file (rather than the default in ~/.ssh/id_rsa)	`ansible_ssh_private_key_file=/path/to/your/.ssh/id_rsa`
Become root using sudo (used if your ansible_user isn't root)	`ansible_become=yes`
Override the python interpreter on the host.	`ansible_python_interpreter=/usr/local/bin/python`

Variables[edit | edit source]

Both group and host specific variables can also be defined outside of the inventory file by placing them within a group_vars and host_vars directory, relative to the inventory file. This might be desirable if there are many variables that need to be defined and allows for easier organization. Regardless of what format your inventory file is written in (INI or YAML), the variables defined in these directories must be written in YAML or JSON.

For example, we can have the following directory structure:

ansible_root
├── group_vars
│   ├── all
│   │   └── general.yaml
│   ├── servers
│   │   └── only-servers.yaml
│   └── webservers
│       └── web-servers.yaml
├── host_vars
│   └── ap1.example.com
└── inventory.ini

Hosts will load variables in the following order:

The playbook, the inventory file,
the group_vars directories (from most general group all, through each of the intermediate parent groups to reach the most specific child group), and
the host_vars directory.

The values that are loaded are then merged or flattened for each host before the playbook is executed. The rule of thumb is that the most specific takes precedence. In the case of host ap1.example.com, it would load its values from: the playbook, the inventory file, group_vars/all, group_vars/servers, host_vars/ap1.example.com. Each subsequent file overrides any previous variables that was set, allowing for generic values to be applied by placing them in the more generic locations first.

Read more on this at: https://docs.ansible.com/ansible/latest/user_guide/intro_inventory.html

Playbook[edit | edit source]

Playbooks define what tasks (or roles which is just a bundle of tasks) a host or host group Ansible needs to perform. When running a playbook with ansible-playbook, tasks are executed in the order they appear and in the order of the host pattern that is given, ensuring that runs are repeatable and reproduceable.

Playbooks can be applied with the ansible-playbook command. After a playbook run, a recap will output the following:

ok - task ran successfully with no changes being made
changed - task ran successfully with changes being made
failed - task failed to run
unreachable - host was unreachable
skipped - task was skipped
ignored - task was ignored
rescued - ?

An example playbook looks like this:

---
- name: Handler demo 1
  hosts: frt01.example.com
  gather_facts: no
  become: yes

  tasks:
    - name: Update Apache configuration
      template:
        src: template.j2
        dest: /etc/httpd/httpd.conf
      notify: Restart Apache

    - name: restart all services
      command: echo "this task will restart all services"
      notify: "restart all services"

  handlers:
    - name: Restart Apache
      service:
        name: httpd
        state: restarted
      listen: "restart all services"

Handlers can be called with notify. Handlers can also listen for a specific event with the listen directive.

Facts[edit | edit source]

You can get all facts by running:

# ansible all -m setup -i inventory.ini

Here are some facts that I commonly use:

# Operating system
"ansible_distribution": "Rocky"
"ansible_distribution_major_version": "8"
"ansible_distribution_release": "Green Obsidian"
"ansible_distribution_version": "8.4"
"ansible_os_family": "Rocky"

# Networking
"ansible_fqdn": "mc44"
"ansible_hostname": "mc44"
"ansible_nodename": "mc44"
"ansible_interfaces": [
    "ib0",
    "lo",
    "eno16"
]

# Machine info
"ansible_memtotal_mb": 192037
"ansible_mounts": []
"ansible_machine": "x86_64"
"ansible_virtualization_type": "NA"
"ansible_memfree_mb": 190562
"ansible_memtotal_mb": 192037
"ansible_swapfree_mb": 0
"ansible_swaptotal_mb": 0

You can determine if the environment is a VM or container by reading the value set under ansible_virtualization_type.

When defining tasks, you can conditionally run something with the when parameter followed by a truth statement. For example, to only run on Red Hat based systems, add when: "ansible_facts['os_family'] == 'RedHat'"

Loops[edit | edit source]

More about loops https://docs.ansible.com/ansible/latest/user_guide/playbooks_loops.html#playbooks-loops

Loops can be done by specifying a list of items and passing it to loop, or with_items.

---
- name: Install Apache
  hosts: frt01.example.com
  gather_facts: no
  become: yes

  tasks:
    - name: Install Apache package
      yum:
        name: httpd
        state: latest
    - name: Open firewall for Apache
      firewalld:
        service: "{{ item }}"
        permanent: yes
        state: enabled
        immediate: yes
      loop:
        - "http"
        - "https"
    - name: Restart and enable the service
      service:
        name: httpd
        state: restarted
        enabled: yes

Quick Demo[edit | edit source]

The quickest way to get your toes wet with Ansible is to try it out with a small set of Docker containers. Using the two docker images (TODO: link to docker files) and docker-compose, we can bring up a small lab to test Ansible with (TODO: link to docker-compose.yml).

Each container has an ansible account with ansible as the password. Using ansible, you can reach all of them using password authentication with the --ask-pass flag. To make the containers use SSH keys going forward, generate a new SSH key on the head node, then run this (TODO: link to playbook) playbook.

You may want to turn off SSH host key checking by creating an ansible.cfg file:

[defaults]
host_key_checking = false

You can then ping all the nodes by running:

# ansible -i inventory.ini all -m shell -a 'hostname'

Precedence[edit | edit source]

See: https://docs.ansible.com/ansible/latest/reference_appendices/general_precedence.html

Tips & Tricks[edit | edit source]

An entire task can be written in one line as a key=value space delimited string. Ansible will parse the string out into a map before passing it to its module.
When defining tasks, you can also call the import_tasks or import_role modules to load a task file or role directory.
Ansible will load all group_vars/group_name/*.yml files as variables. The group_vars directory is relative to the inventory file.
ansible-playbook can be executed against a specific node with the -l <host> limit option.
ansible-playbook can start at a specific task, useful when debugging a specific task, using --start-at-task <task-name>.
You can have ansible-playbook run only a specific set of tasks using the tags feature. Tag roles or tasks you want to run and then call ansible-playbook with --tags <tag>.

- name: do something
  tags: do-something
  debug:
    msg: "hello"

$ ansible-playbook example.yml --tags "do-something"

Distributed shell command[edit | edit source]

You can run commands on all your hosts similar to what you can do with salt-call * cmd.run with ansible.

# ansible all -m shell -a "yum -y update sudo" -i clusters/x/inventory.ini -f 10

Using the shell module, we run yum -y update sudo
We use 10 jobs in parallel (up from the default of 5)

Formatting[edit | edit source]

Tasks with conditions can be written out over newlines. Just use the yaml > operator.

- name: install some packages
  package:
    name: "[[:Template:Packages]]"
    update_cache: yes
    state: latest
  when: >
    ansible_distribution == 'Debian' and
    ansible_distribution_release == my_release and
    some_other_condition != true

Remember that you can specify arrays as inline lists in Ansible. For example:

- name: some task
  tags: ["installation", "task"]

Jinja[edit | edit source]

Test Conditions[edit | edit source]

All test conditions can make use of Jinja templating. This allows for some interesting when conditions when determining when a task or role is to be executed. Some examples below.

Description	Example Condition
if the host is in the `server` group.	`when: 'server' in group_names`
if the host is not in the `server` group.	`when: 'server' not in group_names`
if `some_value` is true, or undefined.	`when: "some_value \| default(true)"`
if `some_value` is undefined	`when: some_value is undefined`
if host is Red Hat	`when: ansible_os_family == "RedHat"`
combining conditionals	`when: ansible_os_family == "RedHat"` `or (ansible_os_family == "Debian" and ansible_os_major_version == "7")`
checking whether a variable contains 'error' anywhere	`when: some_value.find('error') != -1`
Check if an array has items.	`when: some_list \| length > 0`

See more on conditionals at: https://ansible-docs.readthedocs.io/zh/stable-2.0/rst/playbooks_conditionals.html

Align Text[edit | edit source]

Useful when trying to make config files look nice.


Alignment	Code	Example
Left Align	`{{ '%-20s' \| format(my_text ) }}`	`some value`
Center	`{{ my_text \| center(80) }}`	`some value`
Right Align	`{{ '%20s' \| format(my_text ) }}`	`some value`

Comma Delimited List[edit | edit source]

Use the loop.last variable to determine whether this is the last item in the list. You may use either the if-expression, or an actual if block.

{% for item in my_list %}
{{ item }}
{{ "," if not loop.last }}
{% if not loop.last %},{% endif %}
{% endfor %}

Idempotent Random Number[edit | edit source]

Random numbers are useful when configuring many hosts since it lets you spread out tasks over time (in the case of cronjobs) or over different resources (in the case of mounting network filesystems from different endpoints). However, we want the same random number for each host so that each run through of the playbook remains the same. To accomplish this, we can make use of Jinja's random function seeded with the host's inventory name.

vars:
  fileserver_index: {{ 10 | random(seed=inventory_hostname) }}

Doing this, we can use fileserver_index, which contains a value between 0 through 9.

Lookup a DNS name[edit | edit source]

You can use lookup to call dig and lookup a A record. For example:

# ansible localhost -m debug -a "msg={{ lookup('dig', 'nas') }}"

Tasks[edit | edit source]

Disable SELinux[edit | edit source]

- name: Disable SELinux
  selinux: state=disabled

Troubleshooting[edit | edit source]

Import tasks not honoring when condition[edit | edit source]

Given the following task, the when condition is not being honored and is still evaluated:

- name: load tasks if condition is true
  import_tasks: tasks.yml
  when: some_condition_var is defined and some_condition_var is sameas true

The problem here is that import_tasks will load all tasks in tasks.yml at parse time rather than at runtime. This means that all tasks within tasks.yml will be loaded with the when condition applied to each task. With this example, if the condition is false, all tasks that were imported will be skipped.

To not load any of the tasks in tasks.yml when the condition is false, use include_tasks instead.