Comment 2 for bug 1942232

Hi James,

The metadata service is hosted by the "Virtual Router" of a domain, which is also a router and a DHCP server.

The FQDN of the metadata service is "data-server" + a customizable network domain. This domain name is provided by DHCP.

For example, in my CloudStack lab environment, it is "vm.apalia.lan". I've copy-pasted below some command outputs from this specific lab environment.

With a Fedora 33 VM in my CloudStack lab environment, you can see that:
- dig needs the FQDN to find the data-server IP address,
- "host" succeeds with "data-server" but fails with "data-server."
- However, both curl and python's getaddrinfo returns the correct IP address
  of the metadata service when requesting data-server or data-server.

[fedora@fed33 ~]$ grep search /etc/resolv.conf
# configured search domains.
search vm.apalia.lan

[fedora@fed33 ~]$ dig +short data-server
[fedora@fed33 ~]$ dig +short data-server.vm.apalia.lan
10.0.26.1

[fedora@fed33 ~]$ host data-server
data-server.vm.apalia.lan has address 10.0.26.1

[fedora@fed33 ~]$ host data-server.
Host data-server not found: 2(SERVFAIL)

[fedora@fed33 ~]$ curl http://data-server/latest/local-hostname
fed33

[fedora@fed33 ~]$ curl http://data-server./latest/local-hostname
fed33

[fedora@fed33 ~]$ python
Python 3.9.6 (default, Jul 16 2021, 00:00:00)
[GCC 10.3.1 20210422 (Red Hat 10.3.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from socket import getaddrinfo
>>> getaddrinfo("data-server", 80)
[(<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_STREAM: 1>, 6, '', ('10.0.26.1', 80)), (<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_DGRAM: 2>, 17, '', ('10.0.26.1', 80)), (<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_RAW: 3>, 0, '', ('10.0.26.1', 80))]
>>> getaddrinfo("data-server.", 80)
[(<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_STREAM: 1>, 6, '', ('10.0.26.1', 80)), (<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_DGRAM: 2>, 17, '', ('10.0.26.1', 80)), (<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_RAW: 3>, 0, '', ('10.0.26.1', 80))]

With a Fedora 34 VM, you can see that both curl and python's getaddrinfo now
returns the correct IP address when being requested with "data-server" or the
FQDN (here "data-server.vm.apalia.lan") but fail with "data-server."

[fedora@fed34 ~]$ grep search /etc/resolv.conf
# configured search domains.
search vm.apalia.lan

[fedora@fed34 ~]$ dig +short data-server
[fedora@fed34 ~]$ dig +short data-server.vm.apalia.lan
10.0.26.1

[fedora@fed34 ~]$ host data-server
data-server.vm.apalia.lan has address 10.0.26.1

[fedora@fed34 ~]$ host data-server.
Host data-server not found: 2(SERVFAIL)

[fedora@fed34 ~]$ curl http://data-server/latest/local-hostname
fed34

[fedora@fed34 ~]$ curl http://data-server./latest/local-hostname
curl: (6) Could not resolve host: data-server.

[fedora@fed34 ~]$ curl http://data-server.vm.apalia.lan/latest/local-hostname
fed34

[fedora@fed34 ~]$ python
Python 3.9.6 (default, Jul 16 2021, 00:00:00)
[GCC 11.1.1 20210531 (Red Hat 11.1.1-3)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from socket import getaddrinfo
>>> getaddrinfo("data-server", 80)
[(<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_STREAM: 1>, 6, '', ('10.0.26.1', 80)), (<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_DGRAM: 2>, 17, '', ('10.0.26.1', 80)), (<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_RAW: 3>, 0, '', ('10.0.26.1', 80))]
>>> getaddrinfo("data-server.", 80)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python3.9/socket.py", line 953, in getaddrinfo
    for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
socket.gaierror: [Errno -2] Name or service not known

However, CloudStack documents using "data-server." to find the metadata service, so I'll ping some people in the CloudStack community to have their views.