Cannot set hostnames as backend-addresses

[skatsaounis]

Bug Description

The Juju provider allows juju_machines to report their hostname, if wait_for_hostname is set link. This is the only information that someone can get for a Juju machine that runs an application in order to configure HAProxy charm for it.

HAProxy though supports resolvable hostnames as per the documentation link

If that hostname is tried to be added in the ingress-configurator tcp-backend-addresses, then a failure is thrown since it is not validated correctly. Log is attached below.

To Reproduce

# does not work
juju config ingress-configurator tcp-backend-addresses="juju-56c7de-1,juju-56c7de-2,juju-56c7de-3"

# works
juju config ingress-configurator tcp-backend-addresses="10.240.246.4,10.240.246.6,10.240.246.8"

Environment

haproxy 2.8/edge 333
ingress-configurator latest/edge 42
Juju 3.6.14
Juju cloud: LXD

Relevant log output

unit-ingress-configurator-non-tls-1: 10:19:03 INFO unit.ingress-configurator-non-tls/1.juju-log [{'type': 'ip_any_address', 'loc': ('backend_addresses', 0), 'msg': 'value is not a valid IPv4 or IPv6 address', 'input': 'juju-56c7de-1'}, {'type': 'ip_any_address', 'loc': ('backend_addresses', 1), 'msg': 'value is not a valid IPv4 or IPv6 address', 'input': 'juju-56c7de-2'}, {'type': 'ip_any_address', 'loc': ('backend_addresses', 2), 'msg': 'value is not a valid IPv4 or IPv6 address', 'input': 'juju-56c7de-3'}]
unit-ingress-configurator-non-tls-1: 10:19:03 ERROR unit.ingress-configurator-non-tls/1.juju-log Failed to validate haproxy-route-tcp requirements. Invalid config fields: ['backend_addresses-0', 'backend_addresses-1', 'backend_addresses-2']
unit-ingress-configurator-non-tls-1: 10:19:03 ERROR unit.ingress-configurator-non-tls/1.juju-log Error providing haproxy-route-tcp requirements.
Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-ingress-configurator-non-tls-1/charm/src/state/haproxy_route_tcp.py", line 188, in from_charm
    return cls(
           ^^^^
  File "/var/lib/juju/agents/unit-ingress-configurator-non-tls-1/charm/venv/lib/python3.12/site-packages/pydantic/_internal/_dataclasses.py", line 121, in __init__
    s.__pydantic_validator__.validate_python(ArgsKwargs(args, kwargs), self_instance=s)
pydantic_core._pydantic_core.ValidationError: 3 validation errors for HaproxyRouteTcpRequirements
backend_addresses.0
  value is not a valid IPv4 or IPv6 address [type=ip_any_address, input_value='juju-56c7de-1', input_type=str]
backend_addresses.1
  value is not a valid IPv4 or IPv6 address [type=ip_any_address, input_value='juju-56c7de-2', input_type=str]
backend_addresses.2
  value is not a valid IPv4 or IPv6 address [type=ip_any_address, input_value='juju-56c7de-3', input_type=str]

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-ingress-configurator-non-tls-1/charm/src/charm.py", line 141, in _provide_haproxy_route_tcp_requirements
    tcp_requirements = HaproxyRouteTcpRequirements.from_charm(self)
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/var/lib/juju/agents/unit-ingress-configurator-non-tls-1/charm/src/state/haproxy_route_tcp.py", line 204, in from_charm
    raise InvalidHaproxyRouteTcpRequirementsError(
state.haproxy_route_tcp.InvalidHaproxyRouteTcpRequirementsError: Invalid haproxy-route-tcp configuration.

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-ingress-configurator-non-tls-1/charm/src/charm.py", line 114, in _reconcile
    self._provide_haproxy_route_tcp_requirements()
  File "/var/lib/juju/agents/unit-ingress-configurator-non-tls-1/charm/src/charm.py", line 164, in _provide_haproxy_route_tcp_requirements
    raise ProvideHaproxyRouteTcpRequirementsError(
ProvideHaproxyRouteTcpRequirementsError: Failed to provide haproxy-route-tcp requirements.

Additional context

No response

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Thank you for reporting your feedback to us!

The internal ticket has been created: https://warthogs.atlassian.net/browse/ISD-5163.

This message was autogenerated

[Thanhphan1147]

Hi @skatsaounis, we don't allow this for now because as it is right now handling dns resolution is too complex for the following reasons:

1. DNS resolution happens at startup and HAProxy will not start if it fails dns resolution, and a configurator charm that can crash the main charm should not be allowed. So if we add support for DNS names we need to be 100% sure that it's resolvable.
2. The issue with (1) is that while names like juju-56c7de-1 works locally on lxd they won't resolve on other clouds like openstack

We want to support this eventually but there are too many things to consider at the moment if we don't have automatic dns resolution in juju regardless of clouds or a solution for internal DNS.

I'm marking this as a feature for now and keep this open but we won't be able to support this right-away.