Auto Scaling:Automatically execute scripts on ECS instances

Create a custom policy

1. Log on to the RAM console.

2. In the left-side navigation pane, choose Permissions > Policies.

3. Click Create Policy.

4. On the Create Policy page, click the JSON tab and configure the following settings, then click OK.

   Parameter	Setting
   Name	ESSHookPolicyForRunCommand
   Policy Document	See the JSON below

   {
       "Version": "1",
       "Statement": [
           {
               "Action": [
                   "ecs:DescribeInvocationResults",
                   "ecs:DescribeInvocations",
                   "ecs:RunCommand"
               ],
               "Resource": "*",
               "Effect": "Allow"
           },
           {
               "Action": [
                   "ess:CompleteLifecycleAction"
               ],
               "Resource": "*",
               "Effect": "Allow"
           }
       ]
   }

Attach the policy to OOSServiceRole

1. In the left-side navigation pane, choose Identities > Roles.

2. Find OOSServiceRole and click Grant Permission in the Actions column.

3. In the Grant Permission panel, configure the following settings, then click Grant permissions.

   Parameter	Setting
   Resource Scope	Account
   Policies	ESSHookPolicyForRunCommand

Create the lifecycle hook

1. Log on to the Auto Scaling console.

2. In the left-side navigation pane, click Scaling Groups.

3. In the top navigation bar, select the region where your scaling group is located.

4. Click the ID of the scaling group in the Scaling Group Name/ID column, or click Details in the Actions column.

5. On the scaling group details page, click the Lifecycle Hook tab.

6. Click Create Lifecycle Hook.

7. Configure the following settings, then click OK. In the ACS-ESS-LifeCycleRunCommand template section, configure the following parameters: Example script to install Apache:

   Timeout Period is the time Auto Scaling waits for the script to finish before the hook times out. Set it long enough for your script to complete. We recommend that you estimate the period of time required to perform custom operations on instances and configure Timeout Period based on your estimations.

   Parameter	Setting
   Name	ESSHookForRunCommand
   Scaling Activity	Scale-out Event
   Timeout Period	300 (seconds)
   Default Execution Policy	Continue
   Send Notification When Lifecycle Hook Takes Effect	OOS Template > Public Templates > ACS-ESS-LifeCycleRunCommand

   Parameter	Setting
   commandType	RunShellScript
   commandContent	The script to run on each new instance (see example below)
   OOSAssumeRole	OOSServiceRole

   yum install -y httpd
   systemctl start httpd
   systemctl enable httpd

Trigger a scale-out event

Trigger a scale-out event by executing a scaling rule. You can also trigger scale-out events through scheduled tasks or event-triggered tasks.

Lifecycle hooks apply only when Auto Scaling triggers scaling events through scaling rules or tasks. They do not apply when you manually add or remove ECS instances from a scaling group.

1. On the scaling group details page, click the Scaling Rules and Event-triggered Tasks tab.

2. On the Scaling Rules tab, click Create Scaling Rule.

3. Configure the following settings, then click OK.

   Parameter	Setting
   Rule Name	Add1
   Rule Type	Simple Scaling Rule
   Operation	Add 1 Instances

4. Find the Add1 scaling rule and click Execute in the Actions column.

5. In the confirmation dialog box, click OK. Auto Scaling launches one ECS instance and holds it in the Pending Add state while the ESSHookForRunCommand lifecycle hook is active. Auto Scaling notifies OOS to run the O&M tasks in the ACS-ESS-LifeCycleRunCommand template.

Method 1: Check the OOS execution log

Check the OOS execution log to confirm the script ran and to diagnose failures without needing access to the instance.

1. Log on to the OOS console.

2. In the left-side navigation pane, choose Automated Tasks > Task Execution Management.

3. Find the execution record by time and click Details in the Actions column.

4. On the execution details page: For more information, see View the details of an execution.

   • In the Basic Information section, check the execution ID and status.

   • In the Execution Steps and Results section, click a task node to view step-level details and any error output.

Method 2: Check the instance directly

1. On the scaling group details page, click the Instances tab.

2. Find the newly created ECS instance and click its ID in the ECS Instance ID/Name column.

3. In the left-side navigation pane, click Cloud Assistant.

4. In the upper-right corner, click Create/Run Command.

5. Run the following command to check the Apache status. For instructions on running commands via Cloud Assistant, see Create and run a command.

   systemctl status httpd

6. On the Command Execution Result tab, confirm that Apache is installed and in the Active state. This confirms the ACS-ESS-LifeCycleRunCommand template ran successfully.