net: Ephemeral*Network: add connectivity check via URL

We add a new Optional parameter: connectivity_url
This is used in __enter__ to verify if a connection already exists.
If it does exist, no operations are performed.

1 files changed, 34 insertions, 2 deletions

diff --git a/cloudinit/net/__init__.py b/cloudinit/net/__init__.py
index ad98a595..3642fb1f 100644
--- a/cloudinit/net/__init__.py
+++ b/cloudinit/net/__init__.py
@@ -12,6 +12,7 @@ import re
 
 from cloudinit.net.network_state import mask_to_net_prefix
 from cloudinit import util
+from cloudinit.url_helper import UrlError, readurl
 
 LOG = logging.getLogger(__name__)
 SYS_CLASS_NET = "/sys/class/net/"
@@ -647,16 +648,36 @@ def get_ib_hwaddrs_by_interface():
     return ret
 
 
+def has_url_connectivity(url):
+    """Return true when the instance has access to the provided URL
+
+    Logs a warning if url is not the expected format.
+    """
+    if not any([url.startswith('http://'), url.startswith('https://')]):
+        LOG.warning(
+            "Ignoring connectivity check. Expected URL beginning with http*://"
+            " received '%s'", url)
+        return False
+    try:
+        readurl(url, timeout=5)
+    except UrlError:
+        return False
+    return True
+
+
 class EphemeralIPv4Network(object):
     """Context manager which sets up temporary static network configuration.
 
-    No operations are performed if the provided interface is already connected.
+    No operations are performed if the provided interface already has the
+    specified configuration.
+    This can be verified with the connectivity_url.
     If unconnected, bring up the interface with valid ip, prefix and broadcast.
     If router is provided setup a default route for that interface. Upon
     context exit, clean up the interface leaving no configuration behind.
     """
 
-    def __init__(self, interface, ip, prefix_or_mask, broadcast, router=None):
+    def __init__(self, interface, ip, prefix_or_mask, broadcast, router=None,
+                 connectivity_url=None):
         """Setup context manager and validate call signature.
 
         @param interface: Name of the network interface to bring up.
@@ -665,6 +686,8 @@ class EphemeralIPv4Network(object):
             prefix.
         @param broadcast: Broadcast address for the IPv4 network.
         @param router: Optionally the default gateway IP.
+        @param connectivity_url: Optionally, a URL to verify if a usable
+           connection already exists.
         """
         if not all([interface, ip, prefix_or_mask, broadcast]):
             raise ValueError(
@@ -675,6 +698,8 @@ class EphemeralIPv4Network(object):
         except ValueError as e:
             raise ValueError(
                 'Cannot setup network: {0}'.format(e))
+
+        self.connectivity_url = connectivity_url
         self.interface = interface
         self.ip = ip
         self.broadcast = broadcast
@@ -683,6 +708,13 @@ class EphemeralIPv4Network(object):
 
     def __enter__(self):
         """Perform ephemeral network setup if interface is not connected."""
+        if self.connectivity_url:
+            if has_url_connectivity(self.connectivity_url):
+                LOG.debug(
+                    'Skip ephemeral network setup, instance has connectivity'
+                    ' to %s', self.connectivity_url)
+                return
+
         self._bringup_device()
         if self.router:
             self._bringup_router()