AWS Solution Architect Associate (SAA-C02) Review Material – ASG

General

  • Adds or remove EC2 instances according to the load.
  • Has minimum, maximum and desired number of instances.
  • Can automatically register instances to ELB target group
  • Used launch template or launch configuration to determine the instance type, volume, network (VPC & Subnet), security group, key pair of the instance to be launched.
  • Scale-in = remove instances, Scale out = add instances
  • To update ASG you need to provide new launch template or launch configuration.
  • Terminates instances marked as unhealthy by ELB
  • Cool Down Period – No instances will be launched or terminated. Default to 300 seconds.
  • Has Lifecycle Hooks – Additional action can be performed before an instances is in service or terminated.
  • Health Checks:
    • EC2
    • ELB

Types of Scaling

  • Manual
    • By manually changing the minimum, maximum or desired capacity
  • Dynamic (Scale based on metric)
    • Targeted
      • Scale-in when certain metric is above threshold, scale-out when below threshold.
      • example, when Average CPU Utilization is above a limit then increase instance.
      • Does not need to create a CloudWatch Alarm but can use CloudWatch Metrics
      • Can use predefined or customized metrics.
    • Simple
      • Required the use of CloudWatch Alarm
      • Based on CloudWatch Alarm can add/remove/set require instances.
      • Can specify the high / low of the alarm
      • Required instances can be a percentage of the group
    • Step
      • Required the use of CloudWatch Alarm
      • Similar to Simple but can have step adjustment e.g.
        • CPU > 30% add 1 instance
        • CPU > 50% add 2 instances
  • Scheduled (Scale based on schedule)
    • Used when demand is known for a particular period in time.
  • Predictive
    • Use machine learning to predict capacity requirement.
    • Good for:
      • Cyclical traffic, such as high use of resources during regular business hours and low use of resources during evenings and weekends
      • Recurring on-and-off workload patterns, such as batch processing, testing, or periodic data analysis
      • Applications that take a long time to initialize, causing a noticeable latency impact on application performance during scale-out events

Default Termination Policy

  1. Determines the AZ with the most instances
  2. Determine which instances is launched from the oldest launch template/configuration
  3. Determine closest to the billing hour
  4. Terminate in random.

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