sureshanaparti commented on a change in pull request #223:
URL:
https://github.com/apache/cloudstack-documentation/pull/223#discussion_r662791040
##########
File path: source/adminguide/reliability.rst
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@@ -61,25 +61,86 @@ still available but the system VMs will not be able to
contact the
management server.
-HA-Enabled Virtual Machines
----------------------------
+Multiple Management Servers Support on agents
+---------------------------------------------
-The user can specify a virtual machine as HA-enabled. By default, all
-virtual router VMs and Elastic Load Balancing VMs are automatically
-configured as HA-enabled. When an HA-enabled VM crashes, CloudStack
-detects the crash and restarts the VM automatically within the same
-Availability Zone. HA is never performed across different Availability
-Zones. CloudStack has a conservative policy towards restarting VMs and
-ensures that there will never be two instances of the same VM running at
-the same time. The Management Server attempts to start the VM on another
-Host in the same cluster.
+In a Cloudstack environment with multiple management servers, an agent can be
+configured, based on an algorithm, to which management server to connect to.
+This can be useful as an internal loadbalancer or for high availability.
+An administrator is responsible for setting the list of management servers and
+choosing a sorting algorithm using global settings.
+The management server is responsible for propagating the settings to the
+connected agents.
-HA features work with iSCSI or NFS primary storage. HA with local
-storage is not supported.
+Examples of an agent includes, the process responsible for communication to the
+management server, running inside of the Secondary Storage Virtual Machine
+(SSVM), Console Proxy Virtual Machine (CPVM) or the cloudstack-agent running on
+a KVM host.
+
+The three global settings that need to be configured are the following:
+- hosts: a comma seperated list of management server IP addresses
+- indirect.agent.lb.algorithm: The algorithm for the indirect agent LB
+- indirect.agent.lb.check.interval: The preferred host check interval
+ for the agent's background task that checks and switches to an agent's
+ preferred host.
-HA for Hosts
-------------
+These settings can be configured from the global settings page in the UI or
+using the updateConfiguration API call.
+
+The indirect.agent.lb.algorithm setting supports following algorithm options:
+
+- static: Use the list of management server IP addresses as provided.
+- roundrobin: Evenly spread hosts across management servers, based on the
+ host's id.
+- shuffle: Pseudo Randomly sort the list (this is not recommended for
+ production).
+
+.. note::
+ The 'static' and 'roundrobin' algorithms, strictly checks for the order as
+ expected by them, however, the 'shuffle' algorithm just checks for content
+ and not the order of the comma separate management server host addresses.
+
+Any changes to the global settings - `indirect.agent.lb.algorithm` and
+`host` does not require restarting of the management server(s) and the
+agents. A change in these global settings will be propagated to all connected
Review comment:
this seems repeated, it is already mentioned above.
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