How do Agent Managers in HA mode work? (4320023)

High Availability (HA) mode is a configuration in which multiple Agent Managers work together in an HA Partition, where one Agent Manager is a primary host (HA Primary), and others are standby hosts (HA Peers). When configured, agent instances whose types are configured as HA Aware and belong to the same HA Partition are managed by the HA Primary host. If that Agent Manager stops responding or goes offline, the agent instances fail over to another Agent Manager. 

Under a configured HA Partition, a common deployment set of agent types is kept in sync across all HA Peers. Agent packages deployed to that HA Partition are checked for any HA Aware agent types. Any detected HA Aware types are automatically deployed to all other HA Peers.

The FglAM Adapter monitors the deployments of the each Agent Manager host within the named HA Partition. The HA Primary is considered the master in terms of the deployment set and automatically deploys (or undeploys) HA Aware cartridges to each HA Peer. This also happens during cartridge upgrades, when the Adapter automatically pushes out the updates to all of the HA Peers in that HA Partition.

CAUTION: Do not create Agent Manager HA clusters on Agent Manager installations that already contain agent packages. Doing so causes any HA-aware packages, that only exist on the secondary node, to become automatically undeployed. This is because the primary node controls the deployment all HA-aware packages.

Notes:

• When promotions to the HA Primary role are evaluated, the FglAM Adapter gives preference to the HA Peer with the highest priority.
• Until Foglight 6.3.0, once the agent instances failover to another Agent Manager, they will remain in the new host until a user takes action to stop the Agent Manager and initiate the failover to another Agent Manager if available. Starting with Foglight 7.1.0, FglAM HA partitions will now automatically fail back to the highest priority FglAM.
• An alarm for 'Agent Manager HA Failover' is generated to indicate that a failover occurred.

For additional information, please refer to the Configuring the Agent Manager to work in HA mode section of the Foglight Agent Manager Guide.

Determining FglAM HA status

The status of the FglAM HA cluster can be verified from the Agent Managers dashboards or via the HAManager service using the Script Console; for more information refer to How to determine the current HA state of an Agent Manager? (4280439).