Configuring the Ansible inventory
by Uday R. Sawant, William Leemans, Jonathan Hobson, Oliver Pelz
Linux: Powerful Server Administration
- Linux: Powerful Server Administration
- Table of Contents
- Linux: Powerful Server Administration
- Linux: Powerful Server Administration
- Credits
- Preface
- 1. Module 1
- 1. Managing Users and Groups
- 2. Networking
- Introduction
- Connecting to a network with a static IP
- Installing the DHCP server
- Installing the DNS server
- Hiding behind the proxy with squid
- Being on time with NTP
- Discussing load balancing with HAProxy
- Tuning the TCP stack
- Troubleshooting network connectivity
- Securing remote access with OpenVPN
- Securing a network with uncomplicated firewall
- Securing against brute force attacks
- Discussing Ubuntu security best practices
- 3. Working with Web Servers
- Introduction
- Installing and configuring the Apache web server
- Serving dynamic contents with PHP
- Hosting multiple websites with a virtual domain
- Securing web traffic with HTTPS
- Installing Nginx with PHP_FPM
- Setting Nginx as a reverse proxy
- Load balancing with Nginx
- Setting HTTPs on Nginx
- Benchmarking and performance tuning of Apache
- Securing the web server
- Troubleshooting the web server
- 4. Working with Mail Servers
- 5. Handling Databases
- Introduction
- Installing relational databases with MySQL
- Storing and retrieving data with MySQL
- Importing and exporting bulk data
- Adding users and assigning access rights
- Installing web access for MySQL
- Setting backups
- Optimizing MySQL performance – queries
- Optimizing MySQL performance – configuration
- Creating MySQL replicas for scaling and high availability
- Troubleshooting MySQL
- Installing MongoDB
- Storing and retrieving data with MongoDB
- 6. Network Storage
- 7. Cloud Computing
- 8. Working with Containers
- Introduction
- Installing LXD, the Linux container daemon
- Deploying your first container with LXD
- Managing LXD containers
- Managing LXD containers – advanced options
- Setting resource limits on LXD containers
- Networking with LXD
- Installing Docker
- Starting and managing Docker containers
- Creating images with a Dockerfile
- Understanding Docker volumes
- Deploying WordPress using a Docker network
- Monitoring Docker containers
- Securing Docker containers
- 9. Streaming with Ampache
- 10. Communication Server with XMPP
- 11. Git Hosting
- Introduction
- Installing Git
- Creating a local repository with Git CLI
- Storing file revisions with Git commit
- Synchronizing the repository with a remote server
- Receiving updates with Git pull
- Creating repository clones
- Installing GitLab, your own Git hosting
- Adding users to the GitLab server
- Creating a repository with GitLab
- Automating common tasks with Git hooks
- 12. Collaboration Tools
- 13. Performance Monitoring
- 14. Centralized Authentication Service
- 2. Module 2
- 1. Installing CentOS
- Introduction
- Downloading CentOS and confirming the checksum on Windows or OS X
- Creating USB installation media on Windows or OS X
- Performing an installation of CentOS using the graphical installer
- Running a netinstall over HTTP
- Installing CentOS 7 using a kickstart file
- Getting started and customising the boot loader
- Troubleshooting the system in rescue mode
- Updating the installation and enhancing the minimal install with additional administration and development tools
- 2. Configuring the System
- Introduction
- Navigating text files with less
- Introduction to Vim
- Speaking the right language
- Synchronizing the system clock with NTP and the chrony suite
- Setting your hostname and resolving the network
- Building a static network connection
- Becoming a superuser
- Customizing your system banners and messages
- Priming the kernel
- 3. Managing the System
- Introduction
- Knowing and managing your background services
- Troubleshooting background services
- Tracking system resources with journald
- Configuring journald to make it persistent
- Managing users and their groups
- Scheduling tasks with cron
- Synchronizing files and doing more with rsync
- Maintaining backups and taking snapshots
- Monitoring important server infrastructure
- Taking control with GIT and Subversion
- 4. Managing Packages with YUM
- 5. Administering the Filesystem
- 6. Providing Security
- 7. Building a Network
- 8. Working with FTP
- 9. Working with Domains
- 10. Working with Databases
- 11. Providing Mail Services
- 12. Providing Web Services
- 13. Operating System-Level Virtualization
- 14. Working with SELinux
- 15. Monitoring IT Infrastructure
- 1. Installing CentOS
- 3. Module 3
- 1. Working with KVM Guests
- 2. Deploying RHEL "En Masse"
- 3. Configuring Your Network
- 4. Configuring Your New System
- 5. Using SELinux
- 6. Orchestrating with Ansible
- 7. Puppet Configuration Management
- 8. Yum and Repositories
- 9. Securing RHEL 7
- 10. Monitoring and Performance Tuning
- Bibliography
- Index
The Ansible inventory is the heart of the product as it provides a lot of variables about your environment to the deployment mechanism. These variables are known as facts and serve Ansible to make decisions, template text-based files, and so on.
There are several ways of adding information about your environment to your inventory.
The static inventory is basically a mini-formatted file containing the definitions for hosts and groups. Here's what you need to do:
- Create
/etc/ansible/hostswith the following contents:~]# cat << EOF >> /etc/ansible/hosts localhost ansible_connection=local srv1.domain.tld ansible_connection=ssh ansible_ssh_user=root [mail] mail[01..50].domain.tld [mail:vars] dns_servers=[ '8.8.8.8', '8.8.4.4' ] mail_port=25 EOF ~]#
The dynamic inventory file has to be an executable file, generating a JSON string containing information about your hosts and groups. Follow these steps::
- Create an
~/inventory.pyscript with the following contents:-]# cat << EOF >> ~/inventory.py #!/usr/bin/python -tt # -*- coding: utf-8 -*- # vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4 import json def main(): inventory = { '_meta': { 'hostvars': { 'localhost': { 'ansible_connection': 'local' }, 'srv1.domain.tld': { 'ansible_connection': 'ssh', 'ansible_ssh_user': 'root' }, } }, 'all': { 'hosts': [ 'localhost', 'srv1.domain.tld' ] }, 'mail': { 'hosts': [], 'vars': { 'dns_servers': [ '8.8.8.8', '8.8.4.4' ], 'mail_port': 25} } } for x in range(1,50): hostname = 'mail' + ('00%d' % x)[-2:] + '.domain.tld' inventory['_meta']['hostvars'].update({ hostname: {} }) inventory['mail']['hosts'].append(hostname) print json.dumps(inventory, sort_keys=True, indent=4, separators=(',',': ')) if __name__ == '__main__': main() ~]#
- Now, make the script executable, as follows:
~]# chmod +x ~/inventory.py
A host_vars file is a yml-formatted one containing extra facts, which will only be applied to the host with the same name as the file. Simply do the following:
- Create a
host_varsfile forsrv1.domain.tldthrough this command:~]# cat << EOF >> ~/host_vars/srv1.domain.tld.yml ansible_connection: ssh ansible_ssh_user: root EOF ~]#
Like host_vars, group_vars files are yml-formatted ones containing extra facts. These will be applied to the group with the same name as the file. Perform the following:
- Create a
group_varsfile for mail via the following command:~]# cat << EOF >> ~/group_vars/mail.yml dns_servers: [ '8.8.8.8', '8.8.4.4' ] mail_port: 25 EOF ~]#
The inventory file location is set in the Ansible configuration file—look for the line starting with hostfile within the defaults section. This file is either a static file, or a script returning a JSON-formatted list of hosts and groups, as shown in the preceding recipe. Ansible automatically detects whether a file is a script and treats it this way to import information.
There is one caveat, however: the script needs to show the JSON-formatted information by specifying --list.
Ansible can automatically combine the inventory with the host_vars and group_vars files if the latter two directories are in the same directory as the inventory file / script. Take a look at the following:
/etc/ansible/hosts /etc/ansible/host_vars /etc/ansible/host_vars/srv1.domain.tld.yml /etc/ansible/host_vars/... /etc/ansible/group_vars /etc/ansible/group_vars/mail.yml /etc/ansible/group_vars/...
The same can be achieved by putting the host_vars and group_vars directories in the same directory as the playbook you are executing.
Ansible already seeds the inventory with the facts that it retrieves from the host itself. You can easily find out which facts Ansible prepares for your use by executing the following command:
~]# ansible -m setup <hostname>
This will produce a lengthy JSON-formatted output with all the facts Ansible knows about your destination host.
If you want even more information, on RHEL systems, you can install redhat-lsb-core to have access to LSB-specific facts.
Enterprises tend to have databases containing information regarding all their systems for change management. This is an excellent source for the inventory script to get its information.
If you want more detailed information about the Ansible inventory, go to http://docs.ansible.com/ansible/intro_inventory.html.
Shameless self-promotion for a personal project and a tool to automate the inventory calls for a mention of https://github.com/bushvin/inventoryd/.
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