Ansible role hosts

An Ansible role for managing the hosts file (/etc/hosts). Specifically, the responsibilities of this role are to:

• Add the default localhost entry;
• Add entries for basic IPv6 addresses, e.g. ip6-localnet (optional);
• Add entries for Ansible managed hosts (optional);
• Add entries specified in Yaml (optional, see below);
• Add entries specified in text files (optional).

Selecting the correct network interface

When a host has multiple network interfaces, an entry in the hosts file will be generated for each interface with the interface name as suffix. If hosts_network_interface is selected, that IP address will also have a fully qualified domain name included. If hosts_default_domain is set, the FQDN will be generated using it. Otherwise, ansible_fqdn will be used. However, the value of ansible_fqdn can depend on the existing /etc/hosts file which makes this depend on /etc/hosts already being correct in order to make a correct /etc/hosts, a catch-22.

10.10.0.1      node01.example.com node01-eth0 node01
10.30.0.1      node01-eth1
192.168.0.50   node01-ib0

If hosts_network_interface is not set, ansible_hostname and ansible_fqdn will be named according to the interface providing the default route. In cases where hosts_network_interface is not set and there is no default route, only the interface-based names will be generated.

hosts_network_interface can alternatively be set as an array with unique values per host.

The network interfaces lo, docker, and nodelocaldns are automatically excluded. The variable hosts_exclude_interfaces can be used to change the excluded interfaces.

hosts_interface_domain allows including a different FQDN for specific interfaces, either cluster wide or per-host

Requirements

No specific requirements

Role Variables

None of the variables below are required. When not set, the default setting is applied.

Variable	Default	Comments
hosts_file_src		When defined, this path will be copied to the hosts file and all other settings are ignored
hosts_add_basic_ipv6	false	If true, basic IPv6 entries are added (e.g. localhost6, ip6-localnet, etc.)
hosts_add_ansible_managed_hosts	false	If true, an entry for hosts managed by Ansible is added. (†)
hosts_add_ansible_managed_hosts_groups	['all']	Control which host entries are created when using hosts_add_ansible_managed_hosts
hosts_entries	[]	A list of dicts with custom entries to be added to the hosts file. See below for an example.
hosts_file_snippets	[]	A list of files containing host file snippets to be added to the hosts file verbatim.
hosts_ip_protocol	ipv4	When adding Ansible managed hosts, this specifies the IP protocol (ipv4 or ipv6)
hosts_network_interface	''	When adding Ansible managed hosts, this specifies the network interface for which the IP address is used for the default name
hosts_file_backup	no	If yes, backup of host file is created with timestamp

(†) When setting hosts_add_ansible_managed_hosts, an entry for the current host will also be added. Consequently, hosts_add_default_ipv4 doesn't need to be set.

Individual hosts file entries can be added with hosts_entries, a list of dicts with keys name, ip and (optional) aliases. Example:

hosts_entries:
  - name: slashdot
    ip: 216.34.181.45
  - name: gns1
    ip: 8.8.8.8
    aliases:
      - googledns1
      - googlens1
  - name: gns2
    ip: 8.8.4.4
    aliases:
      - googledns2
      - googlens2

Dependencies

No dependencies.

Example Playbook

See the test playbook

Tests for this role are provided in the form of a Vagrant environment that is kept in a separate branch, tests. I use git-worktree(1) to include the test code into the working directory. Instructions for running the tests:

1. Fetch the tests branch: git fetch origin tests
2. Create a Git worktree for the test code: git worktree add tests tests (remark: this requires at least Git v2.5.0). This will create a directory tests/.
3. cd tests/
4. vagrant up will then create a VM and apply a test playbook (test.yml).

You may want to change the base box into one that you like. The current one, bertvv/centos72 was generated using a Packer template from the Boxcutter project with a few modifications.

Contributing

Issues, feature requests, ideas are appreciated and can be posted in the Issues section. Pull requests are also very welcome. Preferably, create a topic branch and when submitting, squash your commits into one (with a descriptive message).

License

BSD, see <LICENSE.md>

Contributors

This role was inspired by the work of soplakanets (including the contribution by astrorafael) and mivok.

• Bert Van Vreckem (maintainer)
• Dheeraj Dwivedi
• Ernestas Poskus
• Mohammed Naser