Putting an Instance Into the Standby State

Application Scenarios

You cannot control the lifecycle of ECS instances in an AS group. The AS group removes unhealthy instances and does not allow you to stop or restart these instances. As a result, some ECS functions are unavailable. For example, you cannot reset the password, or reinstall or change the OS of these instances.

By putting ECS instances into standby state, you can control their lifecycle and perform operations on them as needed, such as stopping the instances. This facilitates management of instances in your AS group and is helpful in a number of different scenarios.

• If you want to change the OS of an ECS added by a scaling action or stop the ECS, you can set the ECS to standby mode. Then you can perform all operations supported by the ECS service. After completing the operations, cancel standby mode for the ECS.

  For example, you can change the AS configuration for your AS group at any time. This configuration will be used by any instance that is created in the AS group. However, the AS group does not update instances that are running. You can stop these instances, and the AS group will replace them. Alternatively, you can set the instances to standby mode, update software on them, and then cancel standby mode for them.

• If an instance in your AS group associated with a load balancer becomes faulty, you can set the instance to standby mode, after which the load balancer will no longer distribute access traffic to the instance. Then you can log in to the instance, locate and rectify the fault, and restart the instance. After the instance recovers, cancel standby mode for the instance to receive traffic again.

Working Rules

• Set instances to standby mode.

After you set an instance to standby mode, the instance will be automatically unbound from the load balancer associated with the AS group. The instance is still in the AS group, but no health check will be performed on the instance. In this case, load on other instances will increase. To reduce load on other instances and ensure proper service running, you can select Add the same number of new instances to the AS group when setting the instance to standby mode.

• An instance can be set to standby mode only when the instance is enabled and the AS group has no ongoing scaling action.
• Scaling actions will not remove standby instances from the AS group.
• You can manually remove standby instances from the AS group.

• Cancel standby mode for instances.

After you cancel standby mode for an instance, it will be in the running state and receive traffic again. If a load balancer is associated with the AS group, the instance will be bound to the load balancer. After the instance starts running properly, a health check will be performed on it again.

Standby mode can be canceled for an instance only when the instance is in standby mode and the AS group has no ongoing scaling action.

Setting Instances to Standby Mode

1. Log in to the AS console.
2. Click the name of the target AS group. The AS group overview page is displayed.
3. Click the Instances tab. In the instance list, select the target instances and choose More > Set to Standby to set the target instances to the standby state.
   Figure 1 Setting instances to standby mode
   

4. In the displayed dialog box, determine whether to select Add the same number of new instances to the AS group based on the site requirements and click OK to set the selected instances to the standby state.

   

   

   After instances are set to the standby state, they will be unbound from the load balancer associated with the AS group. Since no traffic is routed to the standby instance through the load balancer, the load on other instances in the AS group will increase. Adding the same number of new instances to the AS group can prevent this additional load on other instances.

Canceling Standby Mode for Instances

1. Log in to the AS console.
2. Click the name of the target AS group. The AS group overview page is displayed.
3. Click the Instances tab. In the instance list, select the target instances and choose More > Cancel Standby to cancel the standby mode for the instances.
   Figure 2 Cancel standby mode for instances.
   

4. In the displayed dialog box, click OK to cancel the standby mode for the selected instances. The instance lifecycle status changes to Enabled.