Concepts

Fundamentals

Characteristics

Scenarios

The following describes the scenarios of the HA Policy feature.

• Host Business NIC Turns Down:
  If a host business NIC turns down, to ensure high availability of business, all VM instances associated with this NIC are expected to migrate to other hosts.

  • For example, your business VM instances are running MySQL database service which is required to achieve high availability. In this case, you can set the HA mode of these VM instances to NeverStop and turn on the switch corresponding to Abnormal Business NIC Status. Then as long as host resources are sufficient, in case that a host business NIC associated with these VM instances turns down, these VM instances will be auto started on other hosts.
• VM Unexpectedly Stops:
  If a VM instance is unexpectedly stopped, it is expected to auto HA start.

  • For example, your VM instances are running important business applications. To ensure business auto-recovery in case of VM stops due to reasons such as host powered-offs or business overloads, you can set the HA mode of these VM instances to NeverStop. Then if these VM instances are stopped, they are auto started.

HA Policy|Failover Policy

On the Enable HA Policy page or the Overview page of HA Policy, you can modify the following true table to configure failover policies for VM instances.

Management Network Connectivity Status	Storage Network Connectivity Status	Business NIC Status	Fail Over
Normal	Normal	Abnormal	Yes/No
Normal	Abnormal	Normal	Yes/No Note: If the storage type is SharedBlock and this status is Abnormal, VM instances will auto fail over regardless of this configuration.
Normal	Abnormal	Abnormal	Yes/No Note: The failover policy of this scenario follows the preceding two failover policies of this table. If you set both the preceding two policies to No, then this failover policy is set to No. If you set either of the two to Yes, then this failover policy is set to Yes.
Abnormal	Normal	Normal	No Note: If the management network is in Abnormal status, you cannot set this failover policy.

Note:

• For Storage Network Connectivity Status, only shared storage is detected. Local storage is not supported.
• If an L2 network of a VM instance is of the VXLAN type or the L2 network applies the SR-IOV or Smart NIC, and errors occur to the host business NIC associated with this L2 network or occur to the switch port directly connecting to the host business NIC, this VM instance will not fail over.

HA Policy|Advanced Settings

On the Enable HA Policy page or the Overview page of HA Policy, you can modify the advanced settings of HA Policy. They can be classified into the following two categories:

Category	Name	Description
VM Instance	VM Cross-Cluster HA	Specifies whether to enable VM migration across clusters to achieve high availability. Default: false. If set to true, hosts across clusters can be detected to achieve VM high availability. Note: Before you enable this feature, make sure that clusters are well connected.
	Maximum GC Retry Interval of NeverStop VM	The maximum interval of garbage collection (GC) attempts to start up NeverStop VM instances that are stopped unexpectedly. Default: 300. Unit: second.
	Delay of NeverStop VM Startup Attempt	The delay of another retry to start up a NeverStop VM instance after the last startup attempt fails. Default: 60. Unit: second.
	NeverStop VM Scanning Interval	The interval of scanning NeverStop VM instances that fail to start up. Default: 60. Unit: second.
	Sync Speed of HA VM State Update	The synchronization speed of the state of highly available VM instances on the UI. Default: 1. Valid values: -1 to 5, integer. A higher value indicates a lower synchronization speed. However, a higher value lowers system loads because outdated status update notifications are ignored. The value -1 indicates the state of HA VM instances on the UI does not automatically change.
	VM HA Mode	Specifies whether to enable auto restart if VM instances are scheduled or unexpectedly stopped or are errored because of errors occurred to compute, network, or storage resources associated with the VM instances. Valid values: None and NeverStop. If you set HA mode to None, VM instances scheduled or unexpectedly stopped are not auto restarted. If you set HA mode to NeverStop: VM instances scheduled or unexpectedly stopped are auto restarted. If errors occur to compute, network, or storage resources, associated VM instances are auto restarted on another host depending on the HA policy you configure for them. Note: Note that you can specifically set VM HA mode for a VM instance. If you do, this global setting does not take effect on the VM instance.
Host	Abnormal Host Check Interval	The interval that the management node pings abnormal hosts. Default: 5. Unit: second.
	Maximum Attempts to Determine Host Disconnection	The maximum number of failed connections that are required to determine that a host is disconnected. Default: 12.
	Host Successful Connection Period	The time period of a successful connection to a host. Default: 5. Unit: second. If a connection request is responded within the specified time, the connection succeeds.
	Host Successful Connection Possibility	The possibility of successful connections in contrast to failed connections that determine whether a host is successfully connected. Default: 50. Unit: %.
	Minimum Attempts to Determine Successful Host Connection	The minimum number of successful connections that are required to determine that a host is successfully connected. Default: 5.
	Timeout Period of Primary Storage Inspection by Host	The timeout period that a host checks its connection with primary storages. Default: 5. Unit: second.