[Bug 1769682] Re: NFS-based remote root hangs when running 'netplan apply'

[Mathieu Trudel-Lapierre]

** Description changed:

+ [Impact]
+ Netboot users with a remote filesystem over NFS (possibly over other networked filesystems).
+ 
+ [Test cases]
+ 1) Boot a system with its root filesystem over NFS.
+ 2) Run 'sudo netplan apply'
+ 3) Validate that the system remains responsive and keeps connectivity over the same IP address  as it had.
+ 
+ [Regression potential]
+ This SRU changes network properties, and enforces that networkd does not release and re-request an IP address from DHCP when it is restarted. Environments relying on the IP release/renew behavior may find themselves staying on the previous IP address, which might negatively impact connectivity. Changes in connectivity on a system running netplan should be investigated as a potential regression from this SRU. Other regression possibilities would include failure to get a new IP address over time (usually seen as losing connectivity) or possible IP conflicts on a network.
+ 
+ ---
+ 
  With a system booted on the network, with its remote root fs on NFS:
  
  Running 'netplan apply' restarts systemd-networkd, which releases the IP
  received from DHCP. With no IP (and and IP potentially changing), the
  NFS server can't be reached so the system hangs.
  
  'netplan apply' or restarting systemd-networkd should not affect teh
  system, it should continue working normally despite "changing" network
  states, as long as the effective IP remains the same.

** Also affects: nplan (Ubuntu)
   Importance: Undecided
       Status: New

** Also affects: initramfs-tools (Ubuntu)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1769682

Title:
  NFS-based remote root hangs when running 'netplan apply'

Status in initramfs-tools package in Ubuntu:
  New
Status in netplan.io package in Ubuntu:
  New
Status in nplan package in Ubuntu:
  New

Bug description:
  [Impact]
  Netboot users with a remote filesystem over NFS (possibly over other networked filesystems).

  [Test cases]
  1) Boot a system with its root filesystem over NFS.
  2) Run 'sudo netplan apply'
  3) Validate that the system remains responsive and keeps connectivity over the same IP address  as it had.

  [Regression potential]
  This SRU changes network properties, and enforces that networkd does not release and re-request an IP address from DHCP when it is restarted. Environments relying on the IP release/renew behavior may find themselves staying on the previous IP address, which might negatively impact connectivity. Changes in connectivity on a system running netplan should be investigated as a potential regression from this SRU. Other regression possibilities would include failure to get a new IP address over time (usually seen as losing connectivity) or possible IP conflicts on a network.

  ---

  With a system booted on the network, with its remote root fs on NFS:

  Running 'netplan apply' restarts systemd-networkd, which releases the
  IP received from DHCP. With no IP (and and IP potentially changing),
  the NFS server can't be reached so the system hangs.

  'netplan apply' or restarting systemd-networkd should not affect teh
  system, it should continue working normally despite "changing" network
  states, as long as the effective IP remains the same.

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