gce: activate network discovery on every boot (#2128)

Google wants to allow users to make changes on nics while the instance
is stopped. Activate network discovery on every boot.

Additionally, skip the call to `netplan generate` if the rendered
config is the same on subsequent boots.

4 files changed, 44 insertions, 7 deletions

diff --git a/cloudinit/net/netplan.py b/cloudinit/net/netplan.py
index 1c28e16e..8b52a641 100644
--- a/cloudinit/net/netplan.py
+++ b/cloudinit/net/netplan.py
@@ -1,6 +1,7 @@
 # This file is part of cloud-init.  See LICENSE file ...
 
 import copy
+import io
 import ipaddress
 import os
 import textwrap
@@ -277,31 +278,48 @@ class Renderer(renderer.Renderer):
         fpnplan = os.path.join(subp.target_path(target), self.netplan_path)
 
         util.ensure_dir(os.path.dirname(fpnplan))
-        header = self.netplan_header if self.netplan_header else ""
 
         # render from state
         content = self._render_content(network_state)
 
+        # normalize header
+        header = self.netplan_header if self.netplan_header else ""
         if not header.endswith("\n"):
             header += "\n"
+        content = header + content
 
-        mode = 0o600 if features.NETPLAN_CONFIG_ROOT_READ_ONLY else 0o644
+        # determine if existing config files have the same content
+        same_content = False
         if os.path.exists(fpnplan):
+            hashed_content = util.hash_buffer(io.BytesIO(content.encode()))
+            with open(fpnplan, "rb") as f:
+                hashed_original_content = util.hash_buffer(f)
+            if hashed_content == hashed_original_content:
+                same_content = True
+
+        mode = 0o600 if features.NETPLAN_CONFIG_ROOT_READ_ONLY else 0o644
+        if not same_content and os.path.exists(fpnplan):
             current_mode = util.get_permissions(fpnplan)
             if current_mode & mode == current_mode:
                 # preserve mode if existing perms are more strict than default
                 mode = current_mode
-        util.write_file(fpnplan, header + content, mode=mode)
+        util.write_file(fpnplan, content, mode=mode)
 
         if self.clean_default:
             _clean_default(target=target)
-        self._netplan_generate(run=self._postcmds)
+        self._netplan_generate(run=self._postcmds, same_content=same_content)
         self._net_setup_link(run=self._postcmds)
 
-    def _netplan_generate(self, run=False):
+    def _netplan_generate(self, run: bool = False, same_content: bool = False):
         if not run:
             LOG.debug("netplan generate postcmd disabled")
             return
+        if same_content:
+            LOG.debug(
+                "skipping call to `netplan generate`."
+                " reason: identical netplan config"
+            )
+            return
         subp.subp(self.NETPLAN_GENERATE, capture=True)
 
     def _net_setup_link(self, run=False):
diff --git a/cloudinit/net/renderer.py b/cloudinit/net/renderer.py
index 72813e32..c429d068 100644
--- a/cloudinit/net/renderer.py
+++ b/cloudinit/net/renderer.py
@@ -24,7 +24,7 @@ def filter_by_attr(match_name):
 filter_by_physical = filter_by_type("physical")
 
 
-class Renderer:
+class Renderer(abc.ABC):
     def __init__(self, config=None):
         pass
 
diff --git a/cloudinit/sources/DataSourceGCE.py b/cloudinit/sources/DataSourceGCE.py
index 041c8914..27d6089a 100644
--- a/cloudinit/sources/DataSourceGCE.py
+++ b/cloudinit/sources/DataSourceGCE.py
@@ -11,6 +11,7 @@ from cloudinit import dmi
 from cloudinit import log as logging
 from cloudinit import sources, url_helper, util
 from cloudinit.distros import ug_util
+from cloudinit.event import EventScope, EventType
 from cloudinit.net.ephemeral import EphemeralDHCPv4
 from cloudinit.sources import DataSourceHostname
 
@@ -63,6 +64,12 @@ class DataSourceGCE(sources.DataSource):
 
     dsname = "GCE"
     perform_dhcp_setup = False
+    default_update_events = {
+        EventScope.NETWORK: {
+            EventType.BOOT_NEW_INSTANCE,
+            EventType.BOOT,
+        }
+    }
 
     def __init__(self, sys_cfg, distro, paths):
         sources.DataSource.__init__(self, sys_cfg, distro, paths)
diff --git a/cloudinit/util.py b/cloudinit/util.py
index fc777b82..2eb79d33 100644
--- a/cloudinit/util.py
+++ b/cloudinit/util.py
@@ -1725,7 +1725,7 @@ def logexc(log, msg, *args):
     log.debug(msg, exc_info=exc_info, *args)
 
 
-def hash_blob(blob, routine, mlen=None):
+def hash_blob(blob, routine: str, mlen=None) -> str:
     hasher = hashlib.new(routine)
     hasher.update(encode_text(blob))
     digest = hasher.hexdigest()
@@ -1736,6 +1736,18 @@ def hash_blob(blob, routine, mlen=None):
         return digest
 
 
+def hash_buffer(f: io.BufferedIOBase) -> bytes:
+    """Hash the content of a binary buffer using SHA1.
+
+    @param f: buffered binary stream to hash.
+    @return: digested data as bytes.
+    """
+    hasher = hashlib.sha1()
+    for chunk in iter(lambda: f.read(io.DEFAULT_BUFFER_SIZE), b""):
+        hasher.update(chunk)
+    return hasher.digest()
+
+
 def is_user(name):
     try:
         if pwd.getpwnam(name):