Auto Scaling Monitoring

In this, we will learn the concepts of Auto Scaling Monitoring.

Auto Scaling can monitor instances and groups by

Health checks –
- EC2 Auto Scaling periodically performs health checks on instances in the Auto Scaling group
- It identifies unhealthy instances
- Auto Scaling Monitoring finds health status using EC2 status checks, ELB health checks, or custom health checks.
CloudWatch metrics
- EC2 Auto Scaling publishes data points to Amazon CloudWatch
- CloudWatch retrieve statistics about those data points as ordered set of time series data or metrics.
- use these metrics to verify that system is working as expected.
CloudWatch Events
- EC2 Auto Scaling can also submit events to CloudWatch Events
- Event submission is when
- Auto Scaling groups launch or terminate instances,
- lifecycle action occurs.
- Can invoke Lambda function when the event occurs.
SNS notifications
- EC2 Auto Scaling can send Amazon SNS notifications
- SNS sent, when groups launch or terminate instances.
CloudTrail logs
- CloudTrail tracks calls to EC2 Auto Scaling API by
- It stores the information in log files in S3 bucket
- Use log files to monitor activity of your Auto Scaling groups.
- Logs include
  - which requests were made,
  - source IP addresses of requests
  - who made the request
  - when the request was made

EC2 Auto Scaling finds health status of an instance using one or more of the following:

Status checks by EC2 and includes both instance and system status checks.
- Health checks provided by Elastic Load Balancing.
- custom health checks.
Instance is considered unhealthy in any state other than running or if system status is impaired,
unhealthy instance is terminated and replacement is launched
Following states makes instance unhealthy
- stopping
- stopped
- terminating
- terminated

The AWS/AutoScaling namespace includes the following metrics.

Metric	Description
GroupMinSize	The minimum size of the Auto Scaling group.
GroupMaxSize	The maximum size of the Auto Scaling group.
GroupDesiredCapacity	The number of instances that the Auto Scaling group attempts to maintain.
GroupInServiceInstances	The number of instances that are running as part of the Auto Scaling group. This metric does not include instances that are pending or terminating.
GroupPendingInstances	The number of instances that are pending. A pending instance is not yet in service. This metric does not include instances that are in service or terminating.
GroupStandbyInstances	The number of instances that are in a Standby state. Instances in this state are still running but are not actively in service.
GroupTerminatingInstances	The number of instances that are in the process of terminating. This metric does not include instances that are in service or pending.
GroupTotalInstances	The total number of instances in the Auto Scaling group. This metric identifies the number of instances that are in service, pending, and terminating.

It can automate AWS services and respond to system events as
- application availability issues
- resource changes
Events from AWS services are delivered to CloudWatch Events in real time.
Define rules to indicate actions to perform, against events
EC2 Auto Scaling can send events to CloudWatch Events for events
- EC2 Instance-launch Lifecycle Action
- EC2 Instance Launch Successful
- EC2 Instance Launch Unsuccessful
- EC2 Instance-terminate Lifecycle Action
- EC2 Instance Terminate Successful
- EC2 Instance Terminate Unsuccessful

EC2 Auto Scaling can send SNS notifications against following events

Event	Description
autoscaling:EC2_INSTANCE_LAUNCH	Successful instance launch
autoscaling:EC2_INSTANCE_LAUNCH_ERROR	Failed instance launch
autoscaling:EC2_INSTANCE_TERMINATE	Successful instance termination
autoscaling:EC2_INSTANCE_TERMINATE_ERROR	Failed instance termination

The message includes the following information: