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Overview

Polystack Instance HA delivers zero-touch recovery for protected compute workloads. When a compute host becomes unreachable, the service detects the fault, identifies all protected instances on that host, and automatically evacuates them to healthy nodes — without any manual intervention. This page explains the end-to-end detection and recovery flow.
Prerequisites
  • An active Polystack account
  • Instance HA enabled on your platform by an administrator
  • At least one failover segment configured with registered compute hosts

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Core Components

Host Monitor

Continuously polls compute hosts using IPMI out-of-band management or SSH. Declares a host unreachable when it fails to respond within the configured timeout.

Notification Engine

Receives fault signals from monitors, deduplicates events, and routes them to the Recovery Engine as structured notifications.

Recovery Engine

The decision-making core. Identifies protected instances on the failed host and determines the evacuation target based on the segment’s recovery method.

Compute API

Executes the evacuation. Instances are restarted on the selected healthy host using the same image, volume, and network configuration.

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Recovery Flow

The recovery process starts within seconds of fault detection. No human action is required for instances enrolled in an active protection segment.

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Detection Methods

IPMI (Out-of-Band)

The preferred detection method. The host monitor connects to the server’s IPMI interface — which operates independently of the host OS — to verify whether the physical node is powered and responsive.IPMI detection is more reliable than SSH because it does not depend on the host network stack or OS. A host that has kernel-panicked or lost all network interfaces is still detectable via IPMI.
The SSH monitor attempts a TCP connection to the host on port 22. Use this method when IPMI hardware is unavailable.SSH monitoring is susceptible to false positives caused by SSH service restarts, temporary network partitions, or high host load. The monitor implements a configurable retry interval to reduce spurious alerts.
Uses Pacemaker cluster monitoring to detect node failures. Pacemaker tracks cluster membership and triggers a notification when a node is fenced or goes offline.This method integrates with existing Pacemaker/Corosync clusters and leverages STONITH fencing for reliable failure detection.

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Recovery Methods

Each failover segment uses one of four recovery methods. The method is selected when creating the segment.
The recovery method is configured per segment by your administrator. Contact your administrator to understand which method applies to your protection segment. Your administrator can configure this through the deployment console.

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Notification Types

Instance HA generates different notification types depending on the source of the failure:

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Instance Lifecycle During Recovery

The instance ID, name, attached volumes, and network configuration are preserved across the recovery. Only the physical host changes.

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Monitoring in the Dashboard

The Polystack Dashboard provides dedicated pages for monitoring Instance HA:
The Notifications detail page includes a Recovery Progress tab that shows real-time VM evacuation status with auto-refresh every 5 seconds during active recovery. See Monitoring Status for details.

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Next Steps

Protection Segments

Create segments, add hosts, and configure recovery methods

Recovery Workflows

Understand recovery methods and how the engine selects evacuation targets

Monitoring Status

Track active and historical recovery events in the Dashboard

Instance HA Overview

Return to the Instance HA service overview page