How to enumerate network interfaces in Ansible

ansible

I'd like to get an ordered list of the network interfaces on a machine using Ansible. Modern Linux systems don't use eth0, eth1, etc. So the names are unpredictable. On our network we connect the lowest numbered interface to the LAN and the highest to the WAN, so I can use the position of the interface in an ordered list to determine its function.

I am looking for the canonical way to do this in Ansible. So that I can use something like {{ansible_eth0.ipv4.address}}. (Where eth0 is some other name).

Even if I manually set a variable with the name of the interface there seems no way to get the IP of that interface (using the contents of the variable).

I'd like to process the Ansible facts to get what I want rather than running a shell script on the remote system.

Best Answer

The ansible_interfaces fact lists all of the existing network interfaces.

Related Solutions

Using more advanced filters with ansible setup module

Sadly, this is not supported. From the online documentation:

The filter option filters only the first level subkey below ansible_facts.

As the ansible_interface fact is a first level subkey in the structure of the JSON document, the minimum you can access is something like:

# ansible localhost -m setup -a 'filter=ansible_p5p1'
localhost | success >> {
    "ansible_facts": {
        "ansible_p5p1": {
            "active": true,
            "device": "p5p1",
            "ipv4": {
                "address": "10.0.0.2",
                "netmask": "255.255.255.0",
                "network": "10.0.0.0"
            },
            "ipv6": [
                {
                    "address": "fd6c:xxxx:xxxx::2",
                    "prefix": "64",
                    "scope": "global"
                },
                {
                    "address": "fe80::xxxx:xxxx:xxxx:5a56",
                    "prefix": "64",
                    "scope": "link"
                }
           ],
            "macaddress": "xx:xx:xx:xx:xx:xx",
            "module": "foo",
            "mtu": 1500,
            "promisc": false,
            "type": "ether"
        }
    },
    "changed": false
}

If your systems have facter or ohai installed, you can access the same information from ansible:

# ansible localhost -m setup -a 'filter=facter_ipaddress_p5p1'
localhost | success >> {
    "ansible_facts": {
        "facter_ipaddress_p5p1": "10.0.0.2"
    },
    "changed": false
}

Ansible fact from another host

The proper variable appear to be

 - debug: var=hostvars[groups[apphost][0]].inventory_hostname

instead of

 - debug: var=hostvars[apphost].inventory_hostname

Best Answer

Related Solutions

Using more advanced filters with ansible setup module

Ansible fact from another host

Related Topic