Add a test case to check /etc/resolv.conf (#7828)

* Add a test case to check /etc/resolv.conf

Add a test case to verify that the expected nameservers are present (or
not present) in /etc/resolv.conf.

Signed-off-by: Saikrishna Arcot <[email protected]>

* Fix pre-commit check

Signed-off-by: Saikrishna Arcot <[email protected]>

* Add dns test to t0 kvmtest and PR test pipeline

Signed-off-by: Saikrishna Arcot <[email protected]>

---------

Signed-off-by: Saikrishna Arcot <[email protected]>

Author: saiarcot895

.azure-pipelines/pr_test_scripts.yaml

@@ -12,6 +12,7 @@ t0:
   - container_checker/test_container_checker.py
   - dhcp_relay/test_dhcp_relay.py
   - dhcp_relay/test_dhcpv6_relay.py
+  - dns/test_dns_resolv_conf.py
   - generic_config_updater/test_aaa.py
   - generic_config_updater/test_bgp_prefix.py
   - generic_config_updater/test_bgp_speaker.py

tests/common/constants.py

@@ -7,3 +7,12 @@
 IS_BACKEND_TOPOLOGY_KEY = "is_backend_topology"
 # a topology whos name contains the indicator 'backend' will be considered as a backend topology
 BACKEND_TOPOLOGY_IND = "backend"
+# ssh connect default username and password
+DEFAULT_SSH_CONNECT_PARAMS = {
+    "public": {"username": "admin",
+               "password": "YourPaSsWoRd"}
+}
+# resolv.conf expected nameservers
+RESOLV_CONF_NAMESERVERS = {
+    "public": []
+}

tests/dns/test_dns_resolv_conf.py

@@ -0,0 +1,39 @@
+import pytest
+import logging
+from tests.common.constants import RESOLV_CONF_NAMESERVERS
+from tests.common.helpers.assertions import pytest_assert
+from tests.common.utilities import get_image_type
+
+pytestmark = [
+    pytest.mark.topology("any")
+]
+
+logger = logging.getLogger(__name__)
+
+
+def test_dns_resolv_conf(duthost):
+    """verify that /etc/resolv.conf contains the expected nameservers
+
+    Args:
+        duthost: AnsibleHost instance for DUT
+    """
+    # Check SONiC image type and get expected nameservers in /etc/resolv.conf
+    expected_nameservers = set(RESOLV_CONF_NAMESERVERS[get_image_type(duthost=duthost)])
+
+    logger.info("expected nameservers: [{}]".format(" ".join(expected_nameservers)))
+
+    resolv_conf = duthost.shell("cat /etc/resolv.conf", module_ignore_errors=True)
+    pytest_assert(resolv_conf["rc"] == 0, "Failed to read /etc/resolf.conf!")
+    current_nameservers = []
+    for resolver_line in resolv_conf["stdout_lines"]:
+        if not resolver_line.startswith("nameserver"):
+            continue
+        current_nameservers.append(resolver_line.split()[1])
+
+    current_nameservers = set(current_nameservers)
+
+    logger.info("current nameservers: [{}]".format(" ".join(current_nameservers)))
+
+    pytest_assert(not(current_nameservers ^ expected_nameservers),
+                  "Mismatch between expected and current nameservers! Expected: [{}]. Current: [{}].".format(
+                  " ".join(expected_nameservers), " ".join(current_nameservers)))

tests/kvmtest.sh

@@ -154,6 +154,7 @@ test_t0() {
       popd
     else
       tests="\
+      dns/test_dns_resolv_conf.py \
       generic_config_updater/test_aaa.py \
       generic_config_updater/test_bgpl.py \
       generic_config_updater/test_bgp_prefix.py \