** Description changed:

  [Impact]
  
   * 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 an m5.large instance from an encrypted EBS-backed AMI, with
  hibernation enabled.
  
   1. Install ec2-hibinit-agent
  
   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
  
   4. Log in to the instance and observe top still running in screen (to
  prove that the instance resumed and had not been restarted).
  
   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.)
  
  [Regression Potential]
  
   * 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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