vlcty commented 5 years ago

Proposal: Possibility to assign an IPv4 and IPv6 address to ansible_host

Author: Josef Stautner <@vlcty>

Date: 2019-06-01

Status: New
Proposal type: core design
Targeted release: future release
Estimated time to implement: unknown

Motivation

The support and deployment of IPv6 enabled networks and hosts is growing. My hosts are also using IPv6 whenever possible. Yet most of the setups needs some sort if IPv4 connectivity. To smooth the transition I'd like to tell ansible an IPv4 and IPv6 address for each host. Currently you can only set an IPv4 or an IPv6 address.

Problems

You have to choose which IP version you want to support in your network. If you choose IPv4 you will have a hard time in the near future moving on to IPv6.

Solution proposal

Allow ansible_host to be a list of IP adresses like this:

---
ansible_host:
- 2001:0db8:037f:b000:5054:ff:fe22:c14e
- 10.20.20.2

Introduce a new variable like ansible_host6:
```
ansible_host: 10.20.20.2
ansible_host6: "2001:0db8:037f:b000:5054:ff:fe22:c14e"
```
I tend to solution proposal number 2. It should be ensured that IPv6 is preferred over IPv4 but a fallback should be possible.

Dependencies (optional)

None that I know of.

Testing (optional)

Test cases would be:

Prefer IPv6 over IPv4
Fallback to IPv4 if IPv6 fails
Fallback to IPv4 if IPv4 fails

Documentation (optional)

This feature should be documented: https://docs.ansible.com/ansible/latest/user_guide/intro_inventory.html

Anything else?

I've not tested what happens when I set a hostname instead of the IP. I assume that the mechanism would already work. However I don't like the idea of hostnames in ansible. I configure the DNS servers I query with ansible. If something fails or I've to recover from a desaster I can't rely on DNS.

agaffney commented 5 years ago

The ansible_host value is blindly passed to whatever connection method is being used. Each individual connection method would need to have support for specifying multiple possible IP addresses, which isn't really practical. An alternate method would be to have ansible test a connection using each address in the list, but there's no good way to know whether a connection failed because of the IP provided or something like an auth failure or sunspots.