ramo/ansible-notes

Introduction

• Ansible is an IT automation tool.
• Used for
  • Configure systems
  • Deploy software
  • Orchestrate IT tasks (Continuous Deployment, zero downtime rolling updates)

Why Ansible?

• Agentless and uses OpenSSH for connectivity.
• Simple enough to everyone in IT, yet powerful enough to peform more complex tasks.
• Complex scripts can be written in few lines of ansible-playbook

Ansible Concepts

• Control node - The machine from which ansible CLI tools run. This can only be Linux machine.
• Managed node (hosts) - Target devices managed by Ansible.

Inventory

• A list of managed nodes.
• Default inventory file - /etc/ansible/hosts.
• ini format file.
• Alias of a managed node can be given in the beginning of the line.
• Inventory parameters:
  • ansible_connection - ssh/winrm/localhost
  • ansible_poert - 22/5986
  • ansible_user - root/administrator
  • ansible_ssh_pass - Password
  • ansible_password - Windows password.

Sample inventory file

# DB servers
sql_db1 ansible_host=sql01.xyz.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Lin$Pass
sql_db2 ansible_host=sql02.xyz.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Lin$Pass

# Web servers
web_node1 ansible_host=web01.xyz.com ansible_connection=winrm ansible_user=administrator ansible_password=Win$Pass
web_node2 ansible_host=web02.xyz.com ansible_connection=winrm ansible_user=administrator ansible_password=Win$Pass
web_node3 ansible_host=web03.xyz.com ansible_connection=winrm ansible_user=administrator ansible_password=Win$Pass

[db_nodes]
sql_db1
sql_db2

[web_nodes]
web_node1
web_node2
web_node3

[boston_nodes]
sql_db1
web_node1

[dallas_nodes]
sql_db2
web_node2
web_node3

[us_nodes:children]
boston_nodes
dallas_nodes

Playbooks

• Playbook - A single YAML file eg. playbook.yml
• Play - Set of activities (tasks) to be run on hosts. Contains of name hosts tasks
• Task - Single action to be performed on the host. Contains of name and modules.
  • Execute a command
  • Run a script
  • Install a package
  • Shutdown / Restart
• hosts can have node name or group name mentioned in the inventory. When group name is mentioned the play runs simaltaneously on the hosts.
• ansible-doc -l command is used to know more about modules.

Sample Playbook

- name: 'Execute a command to display hosts file on localhost'
  hosts: localhost
  tasks:
    - name: 'Execute a date command'
      command: 'date'

Modules

• The code or binaries that Ansible copies to and executes on managed nodes.
• System, Commands, Files, Database, Cloud, Windows, etc.,

command

• Executes a command on a remote node.

# Simple example
- name: Play1
  hosts: localhost
  tasks:
    - name: 'Execute command date'
      command: date

# Using module parameters
- name: Play2
  hosts: localhost
  tasks:
    - name: 'Display /etc/resolv.conf contents'
      command: cat resolv.conf chdir=/etc

Note
free_form in the module documentation indicate that the module takes free form command to run. There is no parameter actually named free_form.

script

• Runs a local script on a remote node after transferring it.

- name: Play1
  hosts: localhost
  tasks:
    - name: 'Run a script on remote server'
      script: /some/local/script.sh -arg1 -arg2

service

• Manage services - Start, Stop, Restart

- name: Start services in order
  hosts: localhost
  tasks:
    - name: Start the database service
      service: name=postgresql state=started

    - name: Start the httpd service
      service:
        name: httpd
        state: started

lineinfile

• Search for a line in a file and replace it or add it if it doesn't exist.

- name: Add DNS server to resolv.conf
  hosts: localhost
  tasks:
    - name: Add DNS server to resolv.conf
      lineinfile:
        path: /etc/resolv.conf
        line: 'nameserver 10.1.250.10'

Variables

• Stores information that varies with each host
• In inventory file, ansilbe_host, ansible_connection, etc., are variables.
• Defined in the playbook using vars directive. key/value pairs of variables will be child of vars.
• Defined in separate file with host name. Eg: web.yaml where web is the ansible host alias.
• Accessed using {{ variable_name }} Jinja2 templating syntax.

Note
{{ variable_name }} neeed to be written inside quotes if it is not concatenated with other strings.

Conditionals

• Execute different tasks based on value of a data, a variable or the result of previous task.
• when statement is used in task level, if the result is True, the task is executed.
• All variables can be used directly in conditionals without double curly braces.
• == and or operators are used in conditional statements.
• when can be combined with loop statement to apply conditionals in loop. Condition is applied separately on each item.
• Previous task results can be registered in variable using register keyword. String contents of the registered variable using variable.stdout

Loops

• Execute a task multiple times, Ansible offers loop, with_<lookup> and until keywords.
• Any with_* statements which requires lookup within a loop should not be converted to loop keyword.
• loop keyword is equivalent to with_list, and is the best choice for simple loops.

- name: Print list of fruits
  hosts: localhost
  vars:
    fruits:
      - Apple
      - Banana
      - Grapes
      - Orange
  tasks:
    - command: echo "{{ item }}"
      with_items: "{{ fruits }}"

Roles

• A way to package reusable ansible Playbooks and share with others.
• Roles let you automatically load Ansible artifacts (vars, files, tasks, handlers, etc.,).
• Used for orgnaizing the ansible code into tasks, vars, defaults, handlers, templates, etc., directories.
• Ansible Glaxy is a place where you can find many useful Ansible roles.
• ansible-galaxy init <role> command used to create the required directory structure for the role.
• Roles will be referred from roles directory in play's current directory or /etc/ansible/roles directory.
• In /etc/ansible/ansible.cfg roles path is defined as roles_path = /etc/ansible/roles
• To search a role, use ansible-galaxy search <role keyword> or can use the Ansible Galaxy website.
• To use a role, use ansible-galaxy install <role>. The role will be extracted to /etc/ansible/roles directory.
• To list roles, use ansible-galaxy list. Roles path can be found by ansible-config dump | grep ROLE
• Use ansible-galaxy install <role> -p ./roles for installing the role not in the default roles directory.

Advanced Topics

Preparing Windows Server

• Windows targets requires winrm on the machine for Ansible connection. Requires configuration on the target machine.
• pywinrm module need to be installed on the Ansible control machine.

Ansible-Galaxy

• Repository of re-usable ansible roles from the community.

Patterns

• In ansible commands and playbooks, patterns can be used to select specific group of hosts in your inventory.
• Patterns are highly flexible. wildcard, RegEx, exclude, etc., available.

Dynamic Inventory

• Ansible inventory with fluctuating host IP entries, etc., can make use of Dynamic inventory.
• This is achieved by inventory plugins. Eg. aws_ec2 plugin.

Developing Custom Modules

• If required custom logic can be written in Python and can be imported as Ansible custom module.