Lambda function to stop/start RDS instances

Overview

The Lambda function start or stops all RDS instances and RDS Clusters in an account based on a tag assigned to the RDS instance/cluster.

RDS instances and clusters can only be stopped for 7 days and will be restarted automatically by AWS after that period. But sometimes, a RDS instance is only rarely used, and it's really annoying to have to think about stopping the instance every week.

This Lambda function can help to make sure your DB remains in a stopped state (most of the time).

OK, this is not the whole truth, because a RDS instance can only be stopped when it is running. This implies an average uptime of 30 minutes a week when the trigger for the Lambda function goes off once per hour.

Supported tags

RDSDesiredState

Allowed values

• stopped: when the function is run, and the instance state is available, the instance will be stopped
• started: when the function is run, and the instance state is not available, the instance will be started

Requirements for the Lambda function

A policy (inline or not)

The policy has to be attached to the role, and allows the Lambda function to perform certain actions on the RDS instances.

The policy document can be found in the file lambda-rds-start-stop-policy.json, a good name for the policy could be RDSStartStopInstances and the description I used is:

Allows the role or user or group with the policy to start and stop all the RDS instances in the account.

Important: For the Cluster implementation, I had to grant the Lambda permissions on all actions for this to work. I would have expected rds:StopDBCluster or rds:StartDBCluster actions, but they do not exist. I'm waiting for feedback on this in a AWS Support case I logged (CaseId: 5555633581).

A role

The role has to be attached to the function as Execution Role. Assign the policy from the previous step to the role, and use the file lambda-rds-start-stop-trust-relationship.json to define the trust relationship.

A nice name for the role could be LambdaExecutionRoleRDSStartStopInstances.

A trust relationship

A cloudwatch timed trigger

Create a timed trigger in CloudWatch and use it as a trigger for the Lambda function. Name the trigger FireEveryHour, for example.

And set the Schedule expression to rate(1 hour).

The function

Use the function from the file index.js. When defining the function, a trigger has to be created. The trigger will start the Lambda function once every x minutes, the function will loop over all RDS instances, check the DesiredState tag and will act accordingly.

The name of the Lambda function could be RDSStartStopInstances. Use Node.js 8.10 as the Lambda runtime.

Choose the role from ome of the previous step to grant the required permissions to the Lambda function.

Allow the function to run for 30 seconds.