Include old resolv.conf contents without nameservers

localstack-core/localstack/dns/server.py

@@ -809,8 +809,14 @@ def add_resolv_entry(file_path: Path | str = Path("/etc/resolv.conf")):
  try:
  with file_path.open("r+") as outfile:
  PREVIOUS_RESOLV_CONF_FILE = outfile.read()
+ previous_resolv_conf_without_nameservers = [
+ line
+ for line in PREVIOUS_RESOLV_CONF_FILE.splitlines()
+ if not line.startswith("nameserver")
+ ]
  outfile.seek(0)
  outfile.write(content)
+ outfile.write("\n".join(previous_resolv_conf_without_nameservers))
  outfile.truncate()
  except Exception:
  LOG.warning(

tests/unit/test_dns_server.py

@@ -417,6 +417,33 @@ def test_resolv_conf_overwriting(self, tmp_path: Path, monkeypatch):
 
  assert "nameserver 127.0.0.1" in new_contents.splitlines()
 
+ def test_exising_resolv_conf_contents(self, tmp_path: Path, monkeypatch):
+ from localstack.dns import server
+
+ monkeypatch.setattr(server, "in_docker", lambda: True)
+
+ file = tmp_path.joinpath("resolv.conf")
+ with file.open("w") as outfile:
+ print(
+ "nameserver 127.0.0.11\n"
+ "search default.svc.cluster.local svc.cluster.local cluster.local\n"
+ "options ndots:5",
+ file=outfile,
+ )
+
+ add_resolv_entry(file)
+
+ with file.open() as infile:
+ new_contents = infile.read()
+
+ lines = new_contents.splitlines()
+ assert "nameserver 127.0.0.1" in lines
+ assert "search default.svc.cluster.local svc.cluster.local cluster.local" in lines
+ assert "options ndots:5" in lines
+
+ # check the previous value is _not_ in the file
+ assert "nameserver 127.0.0.11" not in lines
+
  def test_no_resolv_conf_overwriting_on_host(self, tmp_path: Path, monkeypatch):
  from localstack.dns import server