Rolling Restart

After modifying the configuration items of a big data component, you need to restart the corresponding service to make new configurations take effect. If you use a normal restart mode, all services or instances are restarted concurrently, which may cause service interruption. To ensure that services are not affected during service restart, you can restart services or instances in batches by rolling restart. For instances in active/standby mode, a standby instance is restarted first and then an active instance is restarted. Rolling restart takes longer than normal restart.

Table 1 provides services and instances that support or do not support rolling restart in the MRS cluster.

**Table 1** Services and instances that support or do not support rolling restart
Service	Instance	Whether to Support Rolling Restart
HDFS	NameNode	Yes
	ZKFC
	JournalNode
	HttpFS
	DataNode
Yarn	ResourceManager	Yes
Yarn	NodeManager	Yes
Hive	MetaStore	Yes
	WebHCat
	HiveServer
MapReduce	JobHistoryServer	Yes
HBase	HMaster	Yes
	RegionServer
	ThriftServer
	RESTServer
Spark	JobHistory	Yes
	JDBCServer	Yes
	SparkResource	No
Hue	Hue	No
Tez	TezUI	No
Loader	Sqoop	No
ZooKeeper	Quorumpeer	Yes
Kafka	Broker	Yes
Kafka	MirrorMaker	No
Flume	Flume	Yes
Flume	MonitorServer	Yes
Storm	Nimbus	Yes
	UI
	Supervisor
	Logviewer

Restrictions

Perform a rolling restart during off-peak hours.
- Otherwise, a rolling restart failure may occur. For example, if the throughput of Kafka is high (over 100 MB/s) during the Kafka rolling restart, the Kafka rolling restart may fail.
- For example, if the requests per second of each RegionServer on the native interface exceed 10,000 during the HBase rolling restart, you need to increase the number of handles to prevent a RegionServer restart failure caused by heavy loads during the restart.
Before the restart, check the number of current requests of HBase. If requests of each RegionServer on the native interface exceed 10,000, increase the number of handles to prevent a failure.
If the number of Core nodes in a cluster is less than six, services may be affected for a short period of time.
Preferentially perform a rolling instance or service restart and select Only restart instances whose configurations have expired.

Performing a Rolling Service Restart

On MRS Manager, click Services and select a service for which you want to perform a rolling restart.
On the Service Status tab page, click More and select Perform Rolling Service Restart.
After you enter the MRS cluster administrator password, the Perform Rolling Service Restart page is displayed. Select Only restart instances whose configurations have expired and click OK to perform rolling restart for the service.
After the rolling restart task is complete, click Finish.

Performing a Rolling Instance Restart

On MRS Manager, click Services and select a service for which you want to perform a rolling restart.
On the Instance tab page, select the instance to be restarted. Click More and select Perform Rolling Instance Restart.
After you enter the MRS cluster administrator password, the Perform Rolling Instance Restart page is displayed. Select Only restart instances whose configurations have expired and click OK to perform rolling restart for the instance.
After the rolling restart task is complete, click Finish.

Perform a Rolling Cluster Restart

On MRS Manager, click Services. The Services page is displayed.
Click More and select Perform Rolling Cluster Restart.
After you enter the MRS cluster administrator password, the Perform Rolling Cluster Restart page is displayed. Select Only restart instances whose configurations have expired and click OK to perform rolling restart for the cluster.
After the rolling restart task is complete, click Finish.

Rolling Restart Parameter Description

Table 2 describes rolling restart parameters.

**Table 2** Rolling restart parameter description
Parameter	Description
Only restart instances whose configurations have expired	Specifies whether to restart only the modified instances in a cluster.
Data Node Instances to Be Batch Restarted	Specifies the number of instances that are restarted in each batch when the batch rolling restart strategy is used. The default value is 1. The value ranges from 1 to 20. This parameter is valid only for data nodes.
Batch Interval	Specifies the interval between two batches of instances for rolling restart. The default value is 0. The value ranges from 0 to 2147483647. The unit is second. Note: Setting the batch interval parameter can increase the stability of the big data component process during the rolling restart. You are advised to set this parameter to a non-default value, for example, 10.
Batch Fault Tolerance Threshold	Specifies the tolerance times when the rolling restart of instances fails to be executed in batches. The default value is 0, which indicates that the rolling restart task ends after any batch of instances fails to be restarted. The value ranges from 0 to 214748364.

Procedure in a Typical Scenario

On MRS Manager, click Services and select HBase. The HBase service page is displayed.
Click the Service Configuration tab, and modify an HBase parameter. After the following dialog box is displayed, click OK to save the configurations.

Do not select Restart the affected services or instances. This option indicates a normal restart. If you select this option, all services or instances will be restarted, which may cause service interruption.
After saving the configurations, click Finish.
Click the Service Status tab.
On the Service Status tab page, click More and select Perform Rolling Service Restart.
After you enter the MRS cluster administrator password, the Perform Rolling Service Restart page is displayed. Select Only restart instances whose configurations have expired and click OK to perform rolling restart for the service.
After the rolling restart task is complete, click Finish.