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.

Fault Scenario	Management Network Connectivity Status	Storage Network Connectivity Status	Business NIC Status	Fail Over
Scenario A: Business NIC Fault	Normal	Normal	Abnormal	Enable/Disable
Scenario B: Storage Network Fault	Normal	Abnormal	Normal	Enable/Disable Note: If the storage type is SharedBlock and this status is Abnormal, VM instances will auto fail over regardless of this configuration.
Scenarios C: Storage Network and Business NIC Fault	Normal	Abnormal	Abnormal	Set as false if both the scenario A and B have the failover policy set as false. Set as true if either of the scenario A or B has the failover policy set as true.
Scenario D: Management Network Fault	Abnormal	Normal	Normal	Disable. The failover cannot be enabled in this scenario.

Note:

• The failover policies take effect on VM instances whose HA modes are set as NeverStop only.
• 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. This setting does not take effect on VM instances whose Bind with Cluster is enabled.
	Maximum Interval for VM Attempt to HA Start	The maximum interval for the system to finish the GC (garbage collection) job and attempt to restart a NeverStop VM according to the HA policy after the VM instance is stopped unexpectedly. Default: 300. Unit: second.
	VM Retry HA Start Interval	The interval for a Neverstop VM to retry an HA start after the previous HA start attempt fails. Default: 60. Unit: second.
	HA VM State Scanning Interval	The interval to scan the status of a NeverStop VM after it fails to HA start. Default: 60. Unit: second.
	HA VM State Update Speed	The speed of updating the state of NeverStop VM instances on the UI. Default: 1. Valid values: -1 to 5. A higher value indicates a lower update speed. However, a lower update speed makes the system ignore a lot of outdated notifications, thus decreasing the system workload. If set to -1, the NeverStop VM states on the UI are not updated automatically.
	VM HA Mode Default Value	Sets the default value of HA mode when creating VM instances. Valid values: None and NeverStop. None: The HA mode of a newly created VM instance is set as None by default. If an unexpected stopping occurs, the VM instance does not reboot automatically. NeverStop: The HA mode of a newly created VM instance is set as NeverStop by default. The VM instance attempts to reboot automatically when it is unexpectedly stopped because of its own errors. The VM instance attempts to migrate to another host automatically if errors occur to the compute, network, or storage resource it is residing on. The VM instance does not reboot automatically if it is stopped manually or through a scheduled job. Note: If you choose NeverStop, make sure that you have enabled HA Policy in Platform Setting. Otherwise, the NeverStop mode does not take effect. You can modify the HA mode of a VM instance individually during or after the creation. After the modification, the VM instance uses the HA mode you specified for it and is not affected by this default value.
Host	Minimum Connection Attempts Required to Determine Host is Disconnected	The maximum times for the system to attempt to connect to a host. If the system fails to connect to the host after the specified times of attempt, the host is determined as disconnected. Default: 12.
	Ping Response Time to Determine Host Connection is Established Successfully	The time period for the system to wait the host response after it pings the host. Receiving a response within this period indicates that the system establishes a successful connection with the host. Default: 5. Unit: second.
	Minimum Successful Connections Required to Determine Host is Re-Connected	The minimum successful connections that the system has to establish with a disconnected host before the host can be determined as re-connected. Default: 5.
	Timeout Period for Host Connecting to Primary Storage	The time for hosts to attempt to connect to primary storage. If a host fails to connect to a primary storage during this period, its connection attempt is determined as timeout. Default: 5. Unit: second.
	Minimum Connection Success Rate to Determine Host is Re-Connected	The minimum rate of successful connections occupied in total connection attempts to determine a disconnected host is successfully re-connected. Default: 50. Unit: %.
	Abnormal Host Status Update Interval	The interval for the system to check and update the status of abnormal hosts. Default: 5. Unit: second.