Add option to check dns with custom dns server, fix gcp ipv6

ch_tools/monrun_checks/dns.py

@@ -1,3 +1,4 @@
+import ipaddress
 import json
 import socket
 from functools import lru_cache
@@ -37,34 +38,48 @@ def __init__(self, fqdn: str, private: bool, strict: bool):
 @click.option(
     "--imdsv2", "imdsv2", is_flag=True, help="Use imdsv2 token for non gcp hosts"
 )
+@click.option(
+    "--nameserver",
+    "nameserver",
+    type=str,
+    help="Custom nameserver to query records from",
+)
 def dns_command(
     cluster: bool,
     private: bool,
     ipv4: bool,
     ipv6: bool,
     imdsv2: bool,
+    nameserver: str = None,
 ) -> Result:
     """
     Check presence and correctness of DNS records.
     """
     err = []
     for record in _get_host_dns(cluster, private):
-        err.extend(_check_fqdn(record, ipv4, ipv6, imdsv2))
+        err.extend(_check_fqdn(record, ipv4, ipv6, imdsv2, nameserver))
 
     if not err:
         return Result(OK)
 
     return Result(CRIT, ", ".join(err))
 
 
-def _check_fqdn(target: _TargetRecord, ipv4: bool, ipv6: bool, imdsv2: bool) -> list:
+def _check_fqdn(
+    target: _TargetRecord, ipv4: bool, ipv6: bool, imdsv2: bool, nameserver: str
+) -> list:
     err = []
     resolver = dns.resolver.Resolver()
+    if nameserver:
+        resolver.nameservers = [nameserver]
 
     def _compare(record_type: str, ip_type: str) -> Tuple[bool, set, set]:
         try:
             actual_addr = set(
-                map(lambda a: a.to_text(), resolver.resolve(target.fqdn, record_type))
+                map(
+                    lambda a: ipaddress.ip_address(a.to_text()),
+                    resolver.resolve(target.fqdn, record_type),
+                )
             )
         except dns.resolver.NXDOMAIN:
             actual_addr = set()
@@ -103,7 +118,7 @@ def _get_host_ip(addr_type: str, imdsv2: bool) -> str:
             headers["X-aws-ec2-metadata-token"] = _get_imdsv2_token()
         resp = requests.get(IP_METADATA_PATHS[addr_type], headers=headers)
     resp.raise_for_status()
-    return resp.text.strip()
+    return ipaddress.ip_network(resp.text.strip())[0]
 
 
 @lru_cache(maxsize=None)