** Description changed:

  [Impact]
  
-  * Some hibernated, then started instances don't restore network
- connectivity keeping the instance unreachable.
+  * Some hibernated, then started instances don't restore network connectivity 
keeping the instance unreachable.
+  * The fix is restarting systemd-networkd on resume.
  
  [Test Case]
  
-  0. Start a ???? instance from an encrypted EBS-backed AMI, with
+  0. Start a ???? instance from an encrypted EBS-backed AMI, with
  hibernation enabled.
  
-  1. Install ec2-hibinit-agent
+  1. Install ec2-hibinit-agent
  
-  2. Start a long running process on the instance, like top in screen.
+  2. Start a long running process on the instance, like top in screen.
  
-  3. Hibernate, then after it finished start the instance on EC2 console
+  3. Hibernate, then after it finished start the instance on EC2 console
  
-  4. Log in to the instance and observe top still running in screen.
+  4. Log in to the instance and observe top still running in screen.
  
-  5. Hibernate, then after it finished start the instance on EC2 console
+  5. Hibernate, then after it finished start the instance on EC2 console
  
-  6. Log in to the instance and observe top still running in screen. 
-    (This second cycle ensures that hibernation works more than once.)
+  6. Log in to the instance and observe top still running in screen.
+    (This second cycle ensures that hibernation works more than once.)
  
  [Regression Potential]
  
-  TODO
+  * Restarting systemd-networkd may cause disturbances in complex networking 
setups, but since the system was hibernated networking was down anyway.
+  * The hook in /lib/systemd/system-sleep/ is ran in parallel to other hooks 
in the same directory and restarting networking may break them. In Bionic the 
following packages use similar hooks:
+ 
+  $ apt-file search /lib/systemd/system-sleep/
+ atop: /lib/systemd/system-sleep/atop-pm
+ battery-stats: /lib/systemd/system-sleep/battery-stats
+ ec2-hibinit-agent: /lib/systemd/system-sleep/hibinit-agent
+ hdparm: /lib/systemd/system-sleep/hdparm
+ lizardfs-chunkserver: /lib/systemd/system-sleep/lizardfs-chunkserver
+ tuxonice-userui: /lib/systemd/system-sleep/tuxonice
+ unattended-upgrades: /lib/systemd/system-sleep/unattended-upgrades
+ 
+ Only lizardfs-chunkserver may be affected because it starts lizardfs-
+ chunkserver.service on resume but by the description it claims to be
+ reliable thus a networking restart is probably tolerated, too. Also it
+ has ~50 popcon count in Debian which may not warrant an extensive
+ investigation nor adding Breaks: without being sure that it breaks.

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https://bugs.launchpad.net/bugs/1830427

Title:
  Instance may loose network connectivity after resuming the 2nd time

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