Serverless Janitor for Amazon Machine Images(AMI)

Automated AMI creation is essential for continuous delivery. If you are using my Serverless AMI Baker or any other automation, clean up of AMIs that are past the rentention date is important to keeps costs under control.

This AWS Lambda function will help you to automatically de-register AMIs beyond retention date and remove the corresponding EBS Snapshots.

You can also follow this article in Youtube

Pre-Requisities

We will need the following pre-requisites to successfully complete this activity,

• Few AMIs with a Tag Key:DeleteOn and Value as Date in this format YYYY-MM-DD
• IAM Role - i.e Lambda Service Role - with below mentioned policy

The image above shows the execution order, that should not be confused with the numbering of steps given here

Step 0: IAM Policy

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "logs:*"
      ],
      "Resource": "arn:aws:logs:*:*:*"
    },
    {
      "Effect": "Allow",
      "Action": "ec2:Describe*",
      "Resource": "*"
    },
    {
      "Effect": "Allow",
      "Action": [
        "ec2:CreateImage",
        "ec2:DeregisterImage",
        "ec2:CreateSnapshot",
        "ec2:DeleteSnapshot",
        "ec2:CreateTags",
        "ec2:ModifySnapshotAttribute",
        "ec2:ResetSnapshotAttribute",
        "iam:Get*"
      ],
      "Resource": [
        "*"
      ]
    }
  ]
}

Step 1 - Configure Lambda Function- Serverless Janitor

The python script is written(and tested) in Python 3.6. Remember to choose the same in AWS Lambda Functions.

Customisations

• Change the global variables at the top of the script to suit your needs.

  • globalVars['findNeedle'] - My AMIs have tag DeleteOn, Set this to the value to suit your requirements
  • globalVars['RetentionDays'] - Set the value you desire, by default it is set to 30 days

• Copy the code from serverless-janitor-for-ami.py in this repo to the lambda function

  • If you have a lot of AMIs, then consider increasing the lambda run time, the default is 3 seconds.

• Save the lambda function

Step 2 - Configure Lambda Triggers

We are going to use Cloudwatch Scheduled Events to take backup everyday.

rate(1 minute)
or
rate(5 minutes)
or
rate(1 day)
# The below example creates a rule that is triggered every day at 12:00pm UTC.
cron(0 12 * * ? *)

If you want to learn more about the above Scheduled expressions, Ref: CloudWatch - Schedule Expressions for Rules

Step 3 - Testing the solution

Create few AMIs and add the Tag DeleteOn with Value as <TODAYS-DATE-IN-YYYY-MM-DD-FORMAT>. If you dont have any, considering trying out my Serverless AMI Baker.

Summary

We have demonstrated how you can automatically identify and delete old and unused AMIs along with their Snapshots.