net/dhcp: handle timeouts for dhcpcd (#5022)

I'm not sure 10 seconds is enough of a timeout.  Azure will retry DHCP
failures, but I expect the reduction from 300s/60s -> 10s will result in
unexpected failures for other clouds where there is no retry.

I see that dhcpcd offers a --timeout option which might be better than
relying on subprocess timeout?  Something to consider.

In the meantime:

- catch the TimeoutExpired exception and raise NoDhcpLeaseError to
  address below traceback

- update the "dhclient" logs to "dhcpcd"

```
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/cloudinit/sources/DataSourceAzure.py", line 851, in _get_data
    crawled_data = util.log_time(
                   ^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/util.py", line 2825, in log_time
    ret = func(*args, **kwargs)
          ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/sources/helpers/azure.py", line 45, in impl
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/sources/DataSourceAzure.py", line 630, in crawl_metadata
    self._setup_ephemeral_networking(timeout_minutes=timeout_minutes)
  File "/usr/lib/python3/dist-packages/cloudinit/sources/helpers/azure.py", line 45, in impl
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/sources/DataSourceAzure.py", line 440, in _setup_ephemeral_networking
    lease = self._ephemeral_dhcp_ctx.obtain_lease()
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/net/ephemeral.py", line 288, in obtain_lease
    self.lease = maybe_perform_dhcp_discovery(
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/net/dhcp.py", line 102, in maybe_perform_dhcp_discovery
    return distro.dhcp_client.dhcp_discovery(interface, dhcp_log_func, distro)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/net/dhcp.py", line 649, in dhcp_discovery
    out, err = subp.subp(
               ^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/subp.py", line 276, in subp
    out, err = sp.communicate(data, timeout=timeout)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/subprocess.py", line 1209, in communicate
    stdout, stderr = self._communicate(input, endtime, timeout)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/subprocess.py", line 2114, in _communicate
    self._check_timeout(endtime, orig_timeout, stdout, stderr)
  File "/usr/lib/python3.12/subprocess.py", line 1253, in _check_timeout
    raise TimeoutExpired(
subprocess.TimeoutExpired: Command '[b'/usr/sbin/dhcpcd', b'--ipv4only', b'--waitip', b'--persistent', b'--noarp', b'--script=/bin/true', b'eth0']' timed out after 10 seconds
```

Signed-off-by: Chris Patterson <cpatterson@microsoft.com>

cloudinit/net/dhcp.py

@@ -15,6 +15,7 @@
 import time
 from contextlib import suppress
 from io import StringIO
+from subprocess import TimeoutExpired
 from typing import Any, Callable, Dict, List, Optional, Tuple
 
 import configobj
@@ -698,9 +699,17 @@ def dhcp_discovery(
                 return lease
             raise NoDHCPLeaseError("No lease found")
 
+        except TimeoutExpired as error:
+            LOG.debug(
+                "dhcpcd timed out after %s seconds: stderr: %r stdout: %r",
+                error.timeout,
+                error.stderr,
+                error.stdout,
+            )
+            raise NoDHCPLeaseError from error
         except subp.ProcessExecutionError as error:
             LOG.debug(
-                "dhclient exited with code: %s stderr: %r stdout: %r",
+                "dhcpcd exited with code: %s stderr: %r stdout: %r",
                 error.exit_code,
                 error.stderr,
                 error.stdout,

tests/unittests/net/test_dhcp.py

@@ -3,6 +3,7 @@
 import os
 import signal
 import socket
+import subprocess
 from textwrap import dedent
 
 import pytest
@@ -1132,9 +1133,11 @@ def test_get_newest_lease_file_from_distro_debian(self, *_):
     # otherwise mock a reply with leasefile
     @mock.patch(
         "os.listdir",
-        side_effect=lambda x: []
-        if x == "/var/lib/NetworkManager"
-        else ["some_file", "!@#$-eth0.lease", "some_other_file"],
+        side_effect=lambda x: (
+            []
+            if x == "/var/lib/NetworkManager"
+            else ["some_file", "!@#$-eth0.lease", "some_other_file"]
+        ),
     )
     @mock.patch("os.path.getmtime", return_value=123.45)
     def test_fallback_when_nothing_found(self, *_):
@@ -1284,6 +1287,51 @@ def test_dhcpcd_discovery_ib(
             ]
         )
 
+    @mock.patch("cloudinit.net.dhcp.subp.which", return_value="/sbin/dhcpcd")
+    @mock.patch("cloudinit.net.dhcp.os.killpg")
+    @mock.patch("cloudinit.net.dhcp.subp.subp")
+    @mock.patch("cloudinit.util.load_json")
+    @mock.patch("cloudinit.util.load_binary_file")
+    @mock.patch("cloudinit.util.write_file")
+    def test_dhcpcd_discovery_timeout(
+        self,
+        m_write_file,
+        m_load_file,
+        m_loadjson,
+        m_subp,
+        m_remove,
+        m_which,
+    ):
+        """Verify dhcpcd timeout results in NoDHCPLeaseError exception."""
+        m_subp.side_effect = [
+            SubpResult("a=b", ""),
+            subprocess.TimeoutExpired(
+                "/sbin/dhcpcd", timeout=6, output="testout", stderr="testerr"
+            ),
+        ]
+        with pytest.raises(NoDHCPLeaseError):
+            Dhcpcd().dhcp_discovery("eth0", distro=MockDistro())
+
+        m_subp.assert_has_calls(
+            [
+                mock.call(
+                    ["ip", "link", "set", "dev", "eth0", "up"],
+                ),
+                mock.call(
+                    [
+                        "/sbin/dhcpcd",
+                        "--ipv4only",
+                        "--waitip",
+                        "--persistent",
+                        "--noarp",
+                        "--script=/bin/true",
+                        "eth0",
+                    ],
+                    timeout=Dhcpcd.timeout,
+                ),
+            ]
+        )
+
 
 class TestMaybePerformDhcpDiscovery:
     def test_none_and_missing_fallback(self):