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Anonymouslemming
Asked: 2017-05-06 12:44:41 +0800 CST

How do I find the name of the second NIC using ansible ?

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I'm deploying something with Ansible to a Linux host, and I need it to listen only on the second NIC on the host.

Looking at the facts available, I can see ansible_interfaces lists all of my NICs, e.g.

 "ansible_interfaces": [
        "lo", 
        "ens9f0", 
        "ens9f1"
 ]

I know that it's not lo, so I can discount that. And by looking at ansible_default_ipv4.alias, I can see that my primary is ens9f0.

In a play / playbook, how could I then work out that ens9f1 is the secondary ?

The use case for this is that I want to do something like the following in a template:

Listen {{ ansible_second_nic.ipv4.address }}

Each machine I work on may have different NIC names, so I can't hard-code these in my roles. Historically I would just assume eth1, but that's no longer safe.

linux

2 Answers

  1. Best Answer

    Take ansible_interfaces, subtract 'lo' and ansible_default_ipv4.alias, take first element of remaining list:

    - debug:
    msg: "{{ ansible_interfaces | difference(['lo',ansible_default_ipv4.alias]) | first }}"
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  2. I noticed the NICs in "ansible_interfaces" don't always come back in order (I'm dealing with 3 and I need to know which is 2nd). So you may have to pipe it through 'sort' first:

    - debug:
msg: "{{ ansible_interfaces | difference(['lo',ansible_default_ipv4.alias]) | sort | first }}"

    I tried using "facter_interfaces" instead of "ansible_interfaces" because it returns the NICs in order but I don't seem to be able to manipulate that output...perhaps because it's a string instead of a list? I'm too new to ansible to know.

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