Modify the AWS RDS Instance size using Lambda Function

This article gives you an overview of the AWS Lambda function to modify the RDS instance class using Python language in Lambda function without stopping the RDS instance.

Let’s follow this article to modify RDS instance using Lambda function.

Steps to create AWS Lambda Function for AWS RDS Instance class

we use the following steps to configure a lambda function.

Step1: Create an IAM Policy

The first step is to create IAM policy to gain access to RDS actions and AWS CloudWatch log events.

Navigate to IAM in the services and click on Policies => Create Policy.

Step2: Create an IAM Role and attach “Lambda_RDS_modification_policy”

In this step, we are creating an IAM role and attach the policy created in the previous step. Click on Roles -> Create Role:

Step3: Create an AWS Lambda Function

Now we will create AWS Lambda function to modify RDS instance class. First you have to select “Author from scratch” -> Function Name -> Runtime (Python3.7 or 3.8) -> Existing Role “RDS_Lambda_Role”

Add inline policy in existing IAM Role

Now, open a new tab for the IAM role and edit the existing Role RDS_Lambda. In the summary page, click on Add Inline Policy

In the Inline policy editor, paste the following JSON. Here, you note that we used the AWS lambda ARN in the resource section. You can copy ARN for your existing lambda ARN.

Lambda ARN follows the format: arn:aws:lambda:Region-AWS Account:function:lambda_function_Name

{   
   "Version": "2012-10-17",
   "Statement": [
{
      "Effect": "Allow",
      "Action": "lambda:GetFunctionConfiguration",
      "Resource": "arn:aws:lambda:us-east-1:11111111111:function:RDSStartFunction"
      }
   ]
}

Step4: Function Code: Scroll down and paste the Python code inside the editor. You need to select appropriate language in the run time. I go with the latest version Python 3.8

Python Code:

Here we are using 2 environment variables:

DBinstance
DBinstanceClass

import sys
import botocore
import boto3
import json
from botocore.exceptions import ClientError
def lambda_handler(event, context):
    rds = boto3.client('rds')
    lambdaFunc = boto3.client('lambda')
    print ('Trying to get Environment variable')
    try:
        funcResponse = lambdaFunc.get_function_configuration(
            FunctionName='RDS_Instance_Modification_Function'
       )
        DBinstance = funcResponse['Environment']['Variables']['DBInstanceName']
        DBinstanceClass = funcResponse['Environment']['Variables']['DBinstanceClass']

        print (f'Starting RDS service for DBInstance : {DBinstance}')
        print (f'RDS instance class : {DBinstanceClass}')


        response = rds.modify_db_instance(DBInstanceIdentifier=DBinstance, DBInstanceClass=DBinstanceClass, ApplyImmediately=True)

        print (f'Success :: {response} ') 
        return json.dumps(dict(abc=123))
    except ClientError as e:
return json.dumps(dict(error=str(e)))

    return json.dumps(dict(abc=12345))

Creating Environment Variables:

Step5: I already created one testdb RDS instance for the testing

Step6: Now we will test the Lambda Function

Click on the “Test” button

First time when you run it and as you already entered the “db.t2.micro” so the result will be like:

But now I will change the “DBinstanceClass” to “db.t2.small” so this time it will successfully modify the AWS RDS instance “testdb” class to “db.t2.small”

Now you will get the following logs after running the lambda function

Here you will see that the RDS instance is now “modifying” status. It will take some time to show you the result as this instance size will be change from “db.t2.micro” to “db.t2.small”