New inventory requires "hostname" even when not needed

Version 2.0.0 has introduced a regression requiring the hostname key to be defined for individual inventory hosts. This is a poor assumption since an environment with name resolution (DNS, local hosts file, or otherwise) should not require such information. For example, this inventory worked in Version 1.x because the hostname csr1000v is resolvable.

$ cat hosts.yaml 
---
csr1000v:
  groups: ["csr"]

$ ping csr1000v -c 1
PING CSR1000V (172.31.55.203) 56(84) bytes of data.
64 bytes from CSR1000V (172.31.55.203): icmp_seq=1 ttl=255 time=1.06 ms

--- CSR1000V ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 1.066/1.066/1.066/0.000 ms

However when running the existing Nornir runbook, an exception is raised because the hostname key is undefined. Even worse, the error message says ip or host must be defined which aren’t even the right keys.

$ python3 get_facts_ios.py
napalm_get**********************************************************************
* csr1000v ** changed : False **************************************************
vvvv napalm_get ** changed : False vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv ERROR
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/nornir/core/task.py", line 62, in start
    r = self.task(self, **self.params)
  File "/usr/local/lib/python3.6/site-packages/nornir/plugins/tasks/networking/napalm_get.py", line 49, in napalm_get
    device = task.host.get_connection("napalm", task.nornir.config)
  File "/usr/local/lib/python3.6/site-packages/nornir/core/inventory.py", line 297, in get_connection
    **self.get_connection_parameters(connection).dict(),
  File "/usr/local/lib/python3.6/site-packages/nornir/core/inventory.py", line 347, in open_connection
    configuration=configuration,
  File "/usr/local/lib/python3.6/site-packages/nornir/plugins/connections/napalm.py", line 43, in open
    connection.open()
  File "/usr/local/lib/python3.6/site-packages/napalm/ios/ios.py", line 138, in open
    netmiko_optional_args=self.netmiko_optional_args,
  File "/usr/local/lib/python3.6/site-packages/napalm/base/base.py", line 82, in _netmiko_open
    **netmiko_optional_args)
  File "/usr/local/lib/python3.6/site-packages/netmiko/ssh_dispatcher.py", line 218, in ConnectHandler
    return ConnectionClass(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/netmiko/base_connection.py", line 170, in __init__
    raise ValueError("Either ip or host must be set")
ValueError: Either ip or host must be set

^^^^ END napalm_get ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I recommend two things:

1. Change the error message to say “The ‘hostname’ key must be defined for each host when name resolution is unavailable”
2. Change the logic to ensure that if name resolution succeeds that the exception is not raised.

[anuzellig]

I agree that an option to autopopulate the hostname would be nice, but for now I’m using the following as a simple workaround:

nr = InitNornir(config_file="config.yaml")
# Assign hostname if it was not set in the hosts file
for key, host in nr.inventory.hosts.items():
    if host.hostname is None:
        host.hostname = key

[dmfigol]

I am against changing the current defaults, but I am open to the feature “auto-populating the hostname” (as long as it is not default!) because “Explicit is better than implicit”. That said, I agree that the error Nick encountered is very confusing. I think we should fix our default connection plugins (netmiko, napalm) to check if the hostname is None and raise a custom exception with a sane message.

@nickrusso42518 you can specify the hostname instead of IP.

---
csr1000v:
  hostname: csr1000v
  groups: ["csr"]