[GitHub] [cloudstack-documentation] nvazquez commented on a diff in pull request #267: Add documentation for live patching systemVMs

[GitBox <gi...@apache.org>]

nvazquez commented on code in PR #267:
URL: https://github.com/apache/cloudstack-documentation/pull/267#discussion_r856344655


##########
source/upgrading/upgrade/_sysvm_restart.rst:
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@@ -15,9 +15,46 @@
 
 .. sub-section included in upgrade notes.
 
-Once you've upgraded the packages on your management servers, you'll
+.. note::

Review Comment:
   This is now very long for a note :)



##########
source/upgrading/upgrade/_sysvm_restart.rst:
##########
@@ -15,9 +15,46 @@
 
 .. sub-section included in upgrade notes.
 
-Once you've upgraded the packages on your management servers, you'll
+.. note::
+
+   From Apache CloudStack version 4.17.0 onward, there is support to live patch 
+   system VMs, namely, SSVM, CPVM, Routers. Live patching provides support 
+   for zero-downtime upgrades, wherein, the System VM software is updated to the
+   latest code version without having to destroy and recreate them / restart them.
+
+   With this feature, users will have a choice wherein they can use the existing system VM template with the latest
+   software by using the live patch feature, or can follow the usual workflow of restarting the
+   system VM to use the latest system VM template. Live Patching system VMs serves to be especially
+   useful in cases when the code version has upgraded but the template hasn't. In such a scenario users
+   will no longer need to restart the system VMs to use the latest code.
+
+   When one attempts to live-patch the system VMs, it pretty much mimics the patching process
+   that happens when booting up the System VMs but with having to shut down the system VMs. 
+   This will update the software packages, which were previously bundled in the systemvm.iso i.e., 
+   agent.zip and cloud-scripts.tgz and restart the services that are present in the /var/cache/cloud/enabled_svcs file
+   in the system VMs. This would mean the following services would be restarted:
+
+            +-----------------+---------------------------+
+            | System VM       |         Services          |
+            +-----------------+---------------------------+
+            | SSVM            | cloud, apache2, portmap   |
+            +-----------------+---------------------------+
+            | CPVM            | cloud                     |
+            +-----------------+---------------------------+
+            | VRs             | haproxy, apache2, dnsmasq |
+            +-----------------+---------------------------+
+
+   Also, with respect to VRs, a network restart without cleanup is initiated to ensure all rules
+   are re-applied. 
+
+   **NOTE:** In case there is an absolute need to upgrade the system VM template due to availability of

Review Comment:
   Could apply ..note in this case



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