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lambda-spot-interruption

Lambda function used resize a auto scaling group based on spot interruption warning.

This lambda function receives a CloudWatch event informing that a instance is going to be removed. With the account id and instance id it drains the instance from the target group or from load balancer and, optionally, increases by one the desired count of another auto scaling group.

This lambda function was created with multi account environments in mind, the function runs with a role which only has the permission to assume other roles.

The account that is running this lambda function needs to enable other accounts to send events to its event bus, the other accounts needs to be configured to route the interruption warning to the main account and add the role to enable the main account to perform the required actions.

sample event:

{
  "version": "0",
  "id": "1e5527d7-bb36-4607-3370-4164db56a40e",
  "detail-type": "EC2 Spot Instance Interruption Warning",
  "source": "aws.ec2",
  "account": "123456789012",
  "time": "1970-01-01T00:00:00Z",
  "region": "us-east-1",
  "resources": [
    "arn:aws:ec2:us-east-1b:instance/i-0b662ef9931388ba0"
  ],
  "detail": {
    "instance-id": "i-0b662ef9931388ba0",
    "instance-action": "terminate"
  }
}

Dependencies

  • Python 3.7
curl -o python3.7.tar.gz https://www.python.org/ftp/python/3.7.4/Python-3.7.4.tgz
tar xvf python3.7.tar.gz
cd Python-3.7.4/
./configure --enable-optimizations --with-ensurepip=install
sudo make altinstall -j $(nproc)
  • AWS Role
On all accounts
On main account

Configuration

Configuration is done through environment variables defined inside the Makefile

Variable Description Requirement Default Value
LAMBDA_ROLE Name of the role to be used by the lambda function YES
ROLE_NAME Name of the role to be assumed by the lambda function YES lambda-spot-interruption
TAGS Lambda function tags Optional
FUNCTION_NAME Lambda function name Optional letsencrypt_internal
DESCRIPTION Lambda function description Optional Lambda function used to provision letsencrypt certificates
REGION Region to deploy the lambda function Optional us-east-1
ZIP_FILE Name of the compressed environment file Optional lambda-spot-interruption.zip
MEMORY_SIZE Maximum memory available to the lambda function Optional 192

Tags that can be configured in the ASG:

Variable Description Requirement Default Value
asgOnDemand Name of the on demand ASG to be increased, add ; MaxDesired=n to limit the max size of the ASG Optional
Limiting the ASG size

If we have a ASG named api-od with a max size of 10 but we don't want the lambda function to increase the desired number above 5, we can configure the asgOnDemand of the spot instance as following: asgOnDemand = api-od; MaxDesired=5

This way the lambda function will not add instances to the ASG if the desired is bigger than 5.

Create an isolated environment

make dependencies

Compress the environment

make pack

Create lambda function

make create-function LAMBDA_ROLE='arn:aws:iam::_ACCOUNT_ID1:role/lambda-spot-interruption-assume' TAGS='name1=value1,name2=value2' ROLE_NAME='lambda-spot-interruption'

Recreate the isolated environment, compress and upload

make deploy