ec2: Allow Ec2 to run in init-local using dhclient in a sandbox.

This branch is a prerequisite for IPv6 support in AWS by allowing Ec2
datasource to query the metadata source version 2016-09-02 about whether
or not it needs to configure IPv6 on interfaces. If version 2016-09-02
is not present, fallback to the min_metadata_version of 2009-04-04. The
DataSourceEc2Local not run on FreeBSD because dhclient in doesn't
support the -sf flag allowing us to run dhclient without filesystem
side-effects.

To query AWS' metadata address @ 169.254.169.254, the instance must have
a dhcp-allocated address configured. Configuring IPv4 link-local
addresses result in timeouts from the metadata service. We introduced a
DataSourceEc2Local subclass which will perform a sandboxed dhclient
discovery which obtains an authorized IP address on eth0 and crawl
metadata about full instance network configuration.

Since ec2 IPv6 metadata is not sufficient in itself to tell us all the
ipv6 knownledge we need, it only be used as a boolean to tell us which
nics need IPv6. Cloud-init will then configure desired interfaces to
DHCPv6 versus DHCPv4.

Performance side note: Shifting the dhcp work into init-local for Ec2
actually gets us 1 second faster deployments by skipping init-network
phase of alternate datasource checks because Ec2Local is configured in
an ealier boot stage. In 3 test runs prior to this change: cloud-init
runs were 5.5 seconds, with the change we now average 4.6 seconds.

This efficiency could be even further improved if we avoiding dhcp
discovery in order to talk to the metadata service from an AWS
authorized dhcp address if there were some way to advertize the dhcp
configuration via DMI/SMBIOS or system environment variables.

Inspecting time costs of the dhclient setup/teardown in 3 live runs the
time cost for the dhcp setup round trip on AWS is:
test 1: 76 milliseconds
         dhcp discovery + metadata: 0.347 seconds
         metadata alone: 0.271 seconds
test 2: 88 milliseconds
         dhcp discovery + metadata: 0.388 seconds
         metadata alone: 0.300 seconds
test 3: 75 milliseconds
         dhcp discovery + metadata: 0.366 seconds
         metadata alone: 0.291 seconds

LP: #1709772

1 files changed, 144 insertions, 0 deletions

diff --git a/cloudinit/net/tests/test_dhcp.py b/cloudinit/net/tests/test_dhcp.py
new file mode 100644
index 00000000..47d8d461
--- /dev/null
+++ b/cloudinit/net/tests/test_dhcp.py
@@ -0,0 +1,144 @@
+# This file is part of cloud-init. See LICENSE file for license information.
+
+import mock
+import os
+from textwrap import dedent
+
+from cloudinit.net.dhcp import (
+    InvalidDHCPLeaseFileError, maybe_perform_dhcp_discovery,
+    parse_dhcp_lease_file, dhcp_discovery)
+from cloudinit.util import ensure_file, write_file
+from tests.unittests.helpers import CiTestCase
+
+
+class TestParseDHCPLeasesFile(CiTestCase):
+
+    def test_parse_empty_lease_file_errors(self):
+        """parse_dhcp_lease_file errors when file content is empty."""
+        empty_file = self.tmp_path('leases')
+        ensure_file(empty_file)
+        with self.assertRaises(InvalidDHCPLeaseFileError) as context_manager:
+            parse_dhcp_lease_file(empty_file)
+        error = context_manager.exception
+        self.assertIn('Cannot parse empty dhcp lease file', str(error))
+
+    def test_parse_malformed_lease_file_content_errors(self):
+        """parse_dhcp_lease_file errors when file content isn't dhcp leases."""
+        non_lease_file = self.tmp_path('leases')
+        write_file(non_lease_file, 'hi mom.')
+        with self.assertRaises(InvalidDHCPLeaseFileError) as context_manager:
+            parse_dhcp_lease_file(non_lease_file)
+        error = context_manager.exception
+        self.assertIn('Cannot parse dhcp lease file', str(error))
+
+    def test_parse_multiple_leases(self):
+        """parse_dhcp_lease_file returns a list of all leases within."""
+        lease_file = self.tmp_path('leases')
+        content = dedent("""
+            lease {
+              interface "wlp3s0";
+              fixed-address 192.168.2.74;
+              option subnet-mask 255.255.255.0;
+              option routers 192.168.2.1;
+              renew 4 2017/07/27 18:02:30;
+              expire 5 2017/07/28 07:08:15;
+            }
+            lease {
+              interface "wlp3s0";
+              fixed-address 192.168.2.74;
+              option subnet-mask 255.255.255.0;
+              option routers 192.168.2.1;
+            }
+        """)
+        expected = [
+            {'interface': 'wlp3s0', 'fixed-address': '192.168.2.74',
+             'subnet-mask': '255.255.255.0', 'routers': '192.168.2.1',
+             'renew': '4 2017/07/27 18:02:30',
+             'expire': '5 2017/07/28 07:08:15'},
+            {'interface': 'wlp3s0', 'fixed-address': '192.168.2.74',
+             'subnet-mask': '255.255.255.0', 'routers': '192.168.2.1'}]
+        write_file(lease_file, content)
+        self.assertItemsEqual(expected, parse_dhcp_lease_file(lease_file))
+
+
+class TestDHCPDiscoveryClean(CiTestCase):
+    with_logs = True
+
+    @mock.patch('cloudinit.net.dhcp.find_fallback_nic')
+    def test_no_fallback_nic_found(self, m_fallback_nic):
+        """Log and do nothing when nic is absent and no fallback is found."""
+        m_fallback_nic.return_value = None  # No fallback nic found
+        self.assertEqual({}, maybe_perform_dhcp_discovery())
+        self.assertIn(
+            'Skip dhcp_discovery: Unable to find fallback nic.',
+            self.logs.getvalue())
+
+    def test_provided_nic_does_not_exist(self):
+        """When the provided nic doesn't exist, log a message and no-op."""
+        self.assertEqual({}, maybe_perform_dhcp_discovery('idontexist'))
+        self.assertIn(
+            'Skip dhcp_discovery: nic idontexist not found in get_devicelist.',
+            self.logs.getvalue())
+
+    @mock.patch('cloudinit.net.dhcp.util.which')
+    @mock.patch('cloudinit.net.dhcp.find_fallback_nic')
+    def test_absent_dhclient_command(self, m_fallback, m_which):
+        """When dhclient doesn't exist in the OS, log the issue and no-op."""
+        m_fallback.return_value = 'eth9'
+        m_which.return_value = None  # dhclient isn't found
+        self.assertEqual({}, maybe_perform_dhcp_discovery())
+        self.assertIn(
+            'Skip dhclient configuration: No dhclient command found.',
+            self.logs.getvalue())
+
+    @mock.patch('cloudinit.net.dhcp.dhcp_discovery')
+    @mock.patch('cloudinit.net.dhcp.util.which')
+    @mock.patch('cloudinit.net.dhcp.find_fallback_nic')
+    def test_dhclient_run_with_tmpdir(self, m_fallback, m_which, m_dhcp):
+        """maybe_perform_dhcp_discovery passes tmpdir to dhcp_discovery."""
+        m_fallback.return_value = 'eth9'
+        m_which.return_value = '/sbin/dhclient'
+        m_dhcp.return_value = {'address': '192.168.2.2'}
+        self.assertEqual(
+            {'address': '192.168.2.2'}, maybe_perform_dhcp_discovery())
+        m_dhcp.assert_called_once()
+        call = m_dhcp.call_args_list[0]
+        self.assertEqual('/sbin/dhclient', call[0][0])
+        self.assertEqual('eth9', call[0][1])
+        self.assertIn('/tmp/cloud-init-dhcp-', call[0][2])
+
+    @mock.patch('cloudinit.net.dhcp.util.subp')
+    def test_dhcp_discovery_run_in_sandbox(self, m_subp):
+        """dhcp_discovery brings up the interface and runs dhclient.
+
+        It also returns the parsed dhcp.leases file generated in the sandbox.
+        """
+        tmpdir = self.tmp_dir()
+        dhclient_script = os.path.join(tmpdir, 'dhclient.orig')
+        script_content = '#!/bin/bash\necho fake-dhclient'
+        write_file(dhclient_script, script_content, mode=0o755)
+        lease_content = dedent("""
+            lease {
+              interface "eth9";
+              fixed-address 192.168.2.74;
+              option subnet-mask 255.255.255.0;
+              option routers 192.168.2.1;
+            }
+        """)
+        lease_file = os.path.join(tmpdir, 'dhcp.leases')
+        write_file(lease_file, lease_content)
+        self.assertItemsEqual(
+            [{'interface': 'eth9', 'fixed-address': '192.168.2.74',
+              'subnet-mask': '255.255.255.0', 'routers': '192.168.2.1'}],
+            dhcp_discovery(dhclient_script, 'eth9', tmpdir))
+        # dhclient script got copied
+        with open(os.path.join(tmpdir, 'dhclient')) as stream:
+            self.assertEqual(script_content, stream.read())
+        # Interface was brought up before dhclient called from sandbox
+        m_subp.assert_has_calls([
+            mock.call(
+                ['ip', 'link', 'set', 'dev', 'eth9', 'up'], capture=True),
+            mock.call(
+                [os.path.join(tmpdir, 'dhclient'), '-1', '-v', '-lf',
+                 lease_file, '-pf', os.path.join(tmpdir, 'dhclient.pid'),
+                 'eth9', '-sf', '/bin/true'], capture=True)])