1-888-317-7920 info@2ndwatch.com

Down to the “Nitty-Gritty”

Now that we have an understanding of how AWS Lambda scheduled events can be expressed, we can dive into a real-world scenario and examine how to set that up using either the API (python and boto3) or CloudFormation.  Because what fun would it be doing it in the web console after all?  And this is a deep-dive, so using the web console would be a distasteful choice anyway.  Also…automation.  Enough said.

Suffice to say, creating the scheduled event for your function in the AWS web console can be done quite easily by selecting “Scheduled Event” from the “Event source type” drop-down list and defining your expression.

The Use Case

Let’s assume we’ve written a nice little Lambda function that will search the EC2 API and find all of our instances running in a region, or multiple regions, and manage EBS snapshot backups for all EBS volumes on any instances with a specific tag.

We could hard-code our parameters in the Lambda function or derive them a number of ways, but let’s assume we’ve done the right thing and have specified them in the Scheduled Event Input parameter.  You might say, “Yeah, but I can just derive the current AWS region during the Lambda function execution, so why bother even providing that input?”  To which I would say:

Lambda is only currently available in the us-east-1, us-west-2, ap-northeast-1, eu-west-1, and eu-central-1 regions. What if you want to manage EC2 backups in ap-southeast-2 or another region where lambda isn’t yet available?

Defining our Inputs

backup_tag (dictionary): A single key/value pair used by the backup function to identify which EC2 instance (any instances with a matching tag) to manage backups on.
Ex. { “Key”: “Environment”, “Value”: “Prod” }

regions (list of strings): A list of region(s) to manage EC2 backups against.
Ex. [ “us-west-2”, “us-west-1”, “us-east-1” ]

support_email (string): An email address to send backup reports, alerts, etc. to.
Ex. “backup.admin@2ndwatch.com”

Those three inputs would be captured as a JSON string like so:

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Lambda Function IAM Role Requirement

Lambda functions require an IAM Role be specified at time of creation.  The Role must have the lambda service added as a “Trusted Entity” so that it can assume the Role.  The Trusted Relationship Policy Document (called AssumeRolePolicyDocument in CloudFormation) should look like this:

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In addition to the Trusted Entity Policy Document, the Role should have a policy, inline or managed, assigned to it that will allow the Lambda function all of the access it needs to AWS resources and APIs (e.g. EC2 describe instances, create snapshots, delete snapshots).  For our use-case the following policy is a good place to start:

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Come back later this week for part 3 of this blog series – Creating the Lambda Function IAM Role.

-Ryan Kennedy, Sr Cloud Consultant

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