Correct use of hostnames in Ansible scripts

[prasadtalasila]

Description

Ansible has three variables, namely inventory_hostname, ansible_hostname and ansible_host for referring to hostname / IP address of a host. We need to select a consistent variable to refer to the following.

1. AutolabJS component name (main server, load balancer, execution node1, execution node2 etc.).
2. Machine on which an AutolabJS component gets installed.
3. Proper settings for connection to the selected machine and the AutolabJS component for installation, configuration and updates.

Expected behavior:
Conventions are set for easy configuration, installation and update of AutolabJS across single and many systems.

Actual behavior:
There is no consistent use of variable names.

References

1. Ansible documentation on working with inventory.
2. Difference between inventory_hostname, ansible_host and ansible_hostname - one, two

[prasadtalasila]

The lessons can be summarized as below.

• inventory_hostname
  app-specific component names which match DNS strings
  Ex: ms.autolabjs.com, lb.autolabjs.com, en1.autolabjs.com etc.

• ansible_host
  IP address to be used to connect to a remote server using SSH, can be "localhost". If this variable is not specified, then inventory_hostname shall be used for connection.
  We can use a domain name too, but the DNS resolution must be in place.

• ansible_port
  SSH port to connect to on remove server, defaults to 22.

• ansible_hostname
  This is the hostname of remote host learnt by Ansible using "gather facts". If gather facts is set to false, then this variable is undefined.
  We don't have control over this variable, DON'T USE IT.

auto-construction of Ansible variables in inventory

Jinja2 templates are supported in Ansible inventory too. For example,

[all:vars]
host_domain=part.one.of.very.long.internal.domain.name.com
ansible_host='{{ inventory_hostname }}.{{ host_domain }}'