You are using Elastic Beanstalk to manage your e-commerce store.
The store is based on an open source e-commerce platform and is deployed across multiple instances in an Auto Scaling group.
Your development team often creates new “extensions” for the e-commerce store.
These extensions include PHP source code and an SQL upgrade script used to make any necessary updates to the database schema.
You have noticed that some extension deployments fail due to an error when running the SQL upgrade script.
After further investigation, you realize that this is because the SQL script is being executed on all of your Amazon EC2 instances.
How would you ensure that the SQL script is only executed once per deployment regardless of how many Amazon EC2 instances are running at the time?
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A. B. C. D.Answer - A.
You can use the container_commands key to execute commands that affect your application source code.
Container commands run after the application and web server have been set up and the application version archive has been extracted, but before the application version is deployed.
Non-container commands and other customization operations are performed before the application source code being extracted.
You can use leader_only to run the command on a single instance or configure a test to run the command when a test command evaluates true.
Leader-only container commands are only executed during environment creation and deployments, while other commands and server customization operations are performed every time an instance is provisioned or updated.
Leader-only container commands are not executed due to launch configuration changes, such as a change in the AMI Id or instance type.
For more information on customizing containers, please visit the below URL:
http://docs.aws.amazon.com/elasticbeanstalk/latest/dg/customize-containers-ec2.htmlThe correct answer to this question is B. Make use of the Amazon EC2 metadata service to query whether the instance is marked as the leader” in the Auto Scaling group. Only execute the script if “true” is returned.
When using Elastic Beanstalk to manage an e-commerce store based on an open-source platform, it is common to create new “extensions” for the store that include PHP source code and SQL upgrade scripts. These scripts are used to make any necessary updates to the database schema. However, when deploying these extensions across multiple instances in an Auto Scaling group, it is possible for the SQL script to be executed on all instances, causing errors and inconsistencies in the database.
To ensure that the SQL script is only executed once per deployment regardless of how many Amazon EC2 instances are running at the time, you can make use of the Amazon EC2 metadata service to query whether the instance is marked as the leader in the Auto Scaling group. If the instance is marked as the leader, the script will be executed; otherwise, it will be skipped.
The leader instance can be determined by querying the metadata service using the following command:
rubycurl http://169.254.169.254/latest/meta-data/spot/instance-action This command will return the current status of the instance in the Auto Scaling group, which can be used to determine whether the instance is the leader. If the status is “launching” or “terminating,” the instance is not the leader. If the status is “none” or “hibernating,” the instance may be the leader.
Once the leader instance has been identified, the SQL upgrade script can be executed using a script that checks the status of the instance using the metadata service before running the script. For example:
bash#!/bin/bash STATUS=$(curl -s http://169.254.169.254/latest/meta-data/spot/instance-action) if [[ "$STATUS" == "none" ]]; then # Run SQL upgrade script here fi This script will check the instance status using the metadata service and only run the SQL upgrade script if the instance is marked as the leader.
In conclusion, using the Amazon EC2 metadata service to determine the leader instance in an Auto Scaling group and only executing the SQL upgrade script on the leader instance is the most effective way to ensure that the script is only executed once per deployment regardless of how many Amazon EC2 instances are running at the time.