Auto Scaling

An Auto Scaling group contains a collection of Amazon EC2 instances that are treated as a logical grouping for the purposes of automatic scaling and management.

An Auto Scaling group also enables you to use Amazon EC2 Auto Scaling features such as health check replacements and scaling policies.

Both maintaining the number of instances in an Auto Scaling group and automatic scaling are the core functionality of the Amazon EC2 Auto Scaling service.

Scaling Policies

Health

ASG + Load Balancers

Lifecycle Hooks

Lifecycle hooks enable you to perform custom actions by pausing instances as an Auto Scaling group launches or terminates them.

When an instance is paused, it remains in a wait state either until you complete the lifecycle action using the complete-lifecycle-action command or the CompleteLifecycleAction operation, or until the timeout period ends (one hour by default).

Scaling Policies

With step scaling and simple scaling, you choose scaling metrics and threshold values for the CloudWatch alarms that trigger the scaling process. You also define how your Auto Scaling group should be scaled when a threshold is in breach for a specified number of evaluation periods.

Step scaling policies and simple scaling policies are two of the dynamic scaling options available for you to use. Both require you to create CloudWatch alarms for the scaling policies. Both require you to specify the high and low thresholds for the alarms. Both require you to define whether to add or remove instances, and how many, or set the group to an exact size.

The main difference between the policy types is the step adjustments that you get with step scaling policies. When step adjustments are applied, and they increase or decrease the current capacity of your Auto Scaling group, the adjustments vary based on the size of the alarm breach.

HealthChecks

Amazon EC2 Auto Scaling can determine the health status of an instance using one or more of the following:

• Status checks provided by Amazon EC2 to identify hardware and software issues that may impair an instance. The default health checks for an Auto Scaling group are EC2 status checks only.

• Health checks provided by Elastic Load Balancing (ELB). These health checks are disabled by default but can be enabled.

• Your custom health checks.

Connection Draining

In order to provide a first-class user experience, you’d like to avoid breaking open network connections while taking an instance out of service, updating its software, or replacing it with a fresh instance that contains updated software.

Imagine each broken connection as a half-drawn web page, an aborted file download, or a failed web service call, each of which results in an unhappy user or customer.

You can now avoid this situation by enabling the new Connection Draining feature for your Classic Load Balancers or Deregistration delay on ALB, NLB or GWLB.

Deregistration Delay

X-Forwarded-For & Proxy Protocol

X-Forwarded-For and Proxy protocol are two alternative versions of gaining visibility of original client IP address when using proxy servers or load balancers

Why ? - X-Forwarded-For & Proxy Protocol

X-Forwarded

Proxy Protocol