Ansible

Core Concepts

Hosts

• Hosts are the servers that Ansible will manage.

Inventory

• The inventory is a list of hosts that Ansible will manage.

  [webserver]
  web1.example.com host=web1.example.com http_port=80 maxRequestsPerChild=808 # Variables for web1.example.com
  web2.example.com ansible_ssh_port=22 ansible_ssh_user=root 
  
  [dbserver]
  db-[1:3].example.com
  db-[a:f].example.com
  
  [dbserver:vars] # Variables for the dbserver group
  ansible_ssh_user=ubuntu
  ansible_ssh_private_key_file=~/.ssh/aws.pem
  
  [servers:children]
  webserver
  dbserver

• parameters

  • ansible_ssh_port: The SSH port number. This can be useful if you have a non-standard SSH port.
  • ansible_ssh_user: The SSH user name. This can be useful if you don’t want to use the current user.
  • ansible_ssh_private_key_file: The SSH private key file. This can be useful if you have a non-standard SSH key file.
  • ansible_ssh_pass: The SSH password. This can be useful if you need to use a password to connect to the host.
  • ansible_sudo_pass: The sudo password. This can be useful if the user you are connecting with does not have passwordless sudo enabled.
  • ansible_connection: The connection type. This can be useful if you want to use a different connection type (for example, paramiko).
  • ansible_python_interpreter: The path to the Python interpreter. This can be useful if you have a non-standard Python installation.
  • ansible_shell_type: The shell type. This can be useful if you want to use a different shell (for example, csh).

• patterns

  • * | all: Matches everything
  • ?: Matches any single character
  • [seq]: Matches any character in seq
  • [!seq]: Matches any character not in seq
  • [start:end]: Matches any character in the range from start to end
  • ~: Using regular expressions
  • --limit: Exclude hosts from the pattern

Ad-Hoc Commands

• Ad-hoc commands are commands that you run on the fly. They are useful for quick changes or one-off commands.

file module

• copy a file to a remote server

  ansible webserver -m file -a "src=/etc/hosts dest=/tmp/hosts"

• create a directory on a remote server

  ansible webserver -m file -a "path=/tmp/testdir state=directory"

• delete a file on a remote server

  ansible webserver -m file -a "path=/tmp/hosts state=absent"

• change the permissions of a file on a remote server

  ansible webserver -m file -a "path=/tmp/hosts mode=0644"

• change the owner and group of a file on a remote server

  ansible webserver -m file -a "path=/tmp/hosts owner=ubuntu group=ubuntu"

manage packages

• install a package on a remote server

  ansible webserver -m yum -a "name=httpd state=present"

• remove a package from a remote server

  ansible webserver -m yum -a "name=httpd state=absent"

• update all packages on a remote server

  ansible webserver -m yum -a "name=* state=latest"

• check if a package is installed on a remote server

  ansible webserver -m yum -a "name=httpd state=latest"

user and group management

• create a user on a remote server

  ansible webserver -m user -a "name=ansible password

• remove a user from a remote server

  ansible webserver -m user -a "name=ansible state=absent"

source control

• clone a git repository to a remote server

  ansible webserver -m git -a "repo=git://foo.example.org/repo.git dest=/srv/myapp version=HEAD"

service management

• start a service on a remote server

  ansible webserver -m service -a "name=httpd state=started"

• stop a service on a remote server

  ansible webserver -m service -a "name=httpd state=stopped"

• restart a service on a remote server

  ansible webserver -m service -a "name=httpd state=restarted"

• check if a service is running on a remote server

  ansible webserver -m service -a "name=httpd state=running"

long-running tasks

• run a command in the background on a remote server

  ansible webserver -B 3600 -P 0 -a "sleep 3600"  # -B: timeout, -P: poll interval
  

• check the status of a long-running task on a remote server

  ansible webserver -m async_status -a "jid=12345"

• kill a long-running task on a remote server

  ansible webserver -m command -a "kill -9 12345"

• gather facts

  ansible webserver -m setup

Modules

• Units of code that Ansible uses to perform tasks.

Tasks

• A task is a unit of work that Ansible will perform. Usually, a task will use a module to perform the work.

Playbooks

• A playbook is a collection of tasks that will be run on a set of hosts.

Examples

• run a command module on a remote server

  - name: Run a command on a remote server
    hosts: all
    tasks:
      - name: Run the `uptime` command
        command: uptime

• run a shell module on a remote server

  - name: Run a shell command on a remote server
    hosts: all
    tasks:
      - name: run a command and ignore the result
        shell: /bin/somecommand
        ignore_errors: True

• run a command using modules by a specific user

  - name: Run a command on a remote server
    hosts: all
    tasks:
      - name: Run the `uptime` command
        command: uptime
        become: yes
        become_user: root

• a playbook to install the Apache web server

  - hosts: webserver
    vars:
      http_port: 80
      maxRequestsPerChild: 808
      max_clients: 200
    remote_user: root
    tasks:
      - name: Install Apache
        yum:
          name: httpd
          state: present
      - name: write the apache config file
        template:
          src: /srv/httpd.j2
          dest: /etc/httpd.conf
        notify: restart apache    # notify: execute after the task
      - name: start apache
        service:
          name: httpd
          state: started
    handlers:
      - name: restart apache
        service:
          name: httpd
          state: restarted

Roles

• Reusable collections of tasks and templates.

• Directory structure:

  - `roles/`
      - `common/`
      - `tasks/`        # Main list of tasks to be executed by the role
          - `main.yml`
      - `handlers/`     # Handlers, which may be used within or outside this role
          - `main.yml`
      - `templates/`    # Template files, which can be used by the `template` module
          - `ntp.conf.j2`
      - `files/`        # Files which can be deployed via the `copy` module
          - `ntp.conf`
      - `vars/`         # Variables for the role
          - `main.yml`
      - `defaults/`     # Default variables for the role
          - `main.yml`
      - `meta/`         # Metadata for the role
          - `main.yml`

• Example of a role:

  - name: run the common role
  hosts: webserver
  roles:
      - common