AWS CloudWatch (Events)

Overview

• AWS Resources publish information about state changes as CloudWatch Events
• Target can execute action upon event
• Rule can route event to Target
• Use cases
  • Invoke Lambda to modify DNS when EC2 instance is launched
  • Direct CloudTrail records to Kinesis
  • Run SSM command on when instance is launced
  • Log AWS API Calls
• Near real-time
• At least-one trigger

Event

• Triggered by:
  • AWS resource changes state, e.g
    • EC2 instance pending->running
    • ASG launches or terminates an instance
    • EBS created a snapshot
    • Code Deploy instance state change
    • Sign-in to AWS Management Console
    • [many other AWS Services]
  • AWS CloudTrail
    • Can be used as intermediary
    • Read/Write calls supported by CloudTrail can be relayed as Events
  • Customer code publishes event (PutEvents)
  • Scheduled (self-triggered)
    • Cron expressions
    • Rate expressions
• Uses JSON format
• Can contain custom payload (useful for Lambda)

Event Bus

• Each AWS account has default bus
• Allows sending events to receiver AWS account
  • On receiver account specify permissions
  • Create a rule 
  • Attach foreign Event Bus as a target

Rule

• matches incoming events and route to targets
• matching is unordered

Target

• Receives event as JSON
  • AWS Systems Manager (Run Command)
  • EC2 API calls
  • ECS tasks
  • Lambda
  • Kinesis Streams 
  • SNS
  • [other AWS Services]
  • Event Bus in another account

References

• http://docs.aws.amazon.com/AmazonCloudWatch/latest/events/DocumentHistory_cwe.html