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Difficulty: Very hardDeployment Strategy Design

An enterprise runs a critical application on Amazon EC2 instances managed by an Auto Scaling group (ASG) behind an Application Load Balancer (ALB). The application must maintain at least 90% of its normal capacity (10 instances) at all times during updates. The solutions architect must design a deployment strategy that routes 10% of incoming traffic to a new version of the application for a 20-minute evaluation period, with the remaining 90% routed to the current version. If HTTP 5xx errors exceed a specified threshold during this period, the deployment must automatically roll back. Due to strict vCPU service quotas in the AWS Region, the organization cannot provision a duplicate ASG of the same size to perform a standard CodeDeploy blue/green deployment. Which two actions should the solutions architect recommend to meet these requirements?

  1. Configure the Application Load Balancer with two target groups: a primary target group pointing to the existing production Auto Scaling group, and a canary target group pointing to a new, separate Auto Scaling group provisioned with 10% of the production group's capacity.Answer
  2. Configure the Application Load Balancer listener rule to use weighted target group routing, directing 90% of traffic to the primary target group and 10% to the canary target group, and use an AWS Lambda function triggered by CloudWatch alarms to reset the canary target group weight to 0% upon failure.Answer
  3. C
    Configure AWS CodeDeploy with a Blue/Green deployment type, selecting the existing Auto Scaling group and using the CodeDeployDefault.EC2Canary10Percent20Minutes deployment configuration to manage the traffic shifting.
  4. D
    Apply a CloudFormation UpdatePolicy with an AutoScalingRollingUpdate to the Auto Scaling group, setting MaxBatchSize to 10% and MinInstancesInService to 90%, and configure the ALB to route 10% of traffic to the updating instances.
  5. E
    Configure AWS CodeDeploy with an In-Place deployment type using the CodeDeployDefault.OneAtATime configuration, and enable ALB traffic shifting in the deployment group to isolate 10% of traffic to the newly deployed instances.

Answer

The solutions architect should configure the Application Load Balancer with two target groups (one for the primary ASG and one for the 10% canary ASG) and configure the ALB listener rule with weighted target group routing combined with an AWS Lambda function triggered by CloudWatch alarms to reset the weight to 0% on failure.
To achieve a 10% canary deployment on EC2 without duplicating the entire ASG (which would violate vCPU service quotas), the Solutions Architect must design a custom deployment strategy. This is done by creating a separate target group and a smaller Auto Scaling group sized to 10% of the primary ASG (1 instance). An ALB listener rule with weighted target groups is used to shift 10% of the traffic to the canary group. If a failure occurs, a Lambda function triggered by CloudWatch alarms can automatically reset the weight to 0%, executing a rollback without affecting the primary production fleet.

Step-by-Step Solution

1
Analyze deployment constraints
Determine that native CodeDeploy blue/green deployments cannot be used because they copy the entire Auto Scaling group, which violates the regional vCPU quota constraint. Also, realize that CodeDeploy canary/linear traffic shifting is not supported on EC2.
This rules out native CodeDeploy options and establishes the need for a custom deployment strategy.
2
Design the target groups and Auto Scaling groups
Define a primary target group for the existing 10-instance ASG, and provision a separate, smaller ASG (with 1 instance, representing 10% capacity) mapped to a canary target group.
This satisfies the requirement to maintain 90% capacity during deployments without exceeding the region's vCPU quota.
3
Configure load balancer routing
Configure the ALB listener rule with weighted target group routing, mapping 90% weight to the primary target group and 10% weight to the canary target group.
This implements the 10% canary traffic split required for evaluation.
4
Implement automated rollback monitoring
Set up a CloudWatch alarm for HTTP 5xx errors and configure it to trigger an AWS Lambda function that resets the canary target group weight to 0% and scales down the canary ASG if error thresholds are exceeded.
This guarantees a fast, automated rollback within the required time window.

Key Concept

Custom canary deployment design on AWS EC2 when native CodeDeploy deployment options are limited by region quotas or platform capabilities.
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Topics

Deployment Strategy Design

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