lambda-ec2-dns

Designed to be integrated with Codeship.

Event flow

CloudWatch Rule -> Lambda -> Route53

CloudFormation

Because plugging all the moving parts together by hand is painful, I've put as much as possible into a CloudFormation template.

It takes three parameters:

HostedZoneId which should have the Route53 hosted zone ID of the zone you want your new DNS entries to appear in. Eg. Z354G969XV9QZ9
HostedZoneName which should have the domain name under which your DNS entries should be created. eg. apse2.mydomain.com.; note that this must have a trailing dot.
CodeshipIAMUser which should have the name of the IAM user you want to use for autodeploying this code with Codeship.

When the template is deployed (see commands in the Stack Creation section) the following resources are created:

Codeship IAM policy (and attaches it to the specified user)
IAM role for the Lambda function
IAM policy for the Lambda function allowing it to do the things
Lambda function
CloudWatch Events Rule to trigger the Lambda function
Production and Development aliases for the function

Stack Creation

# note here that the HostedZoneName parameter must have a trailing .
# ie. "your.domain." *not* "your.domain"
aws --region=your-region cloudformation create-stack \
  --stack-name asoe-autodns \
  --template-body file://asoe-autodns.json \
  --capabilities CAPABILITY_IAM \
  --parameters \
    ParameterKey=HostedZoneId,ParameterValue=YOUR_HOSTED_ZONE_ID \
    ParameterKey=HostedZoneName,ParameterValue=your.domain. \
    ParameterKey=CodeshipIAMUser,ParameterValue=svc_codeship

Stack Update

# note here that the HostedZoneName parameter must have a trailing .
# ie. "your.domain." *not* "your.domain"
aws --region your-region cloudformation update-stack \
  --stack-name asoe-autodns \
  --template-body file://asoe-autodns.json \
  --capabilities CAPABILITY_IAM \
  --parameters \
    ParameterKey=HostedZoneId,ParameterValue=YOUR_HOSTED_ZONE_ID \
    ParameterKey=HostedZoneName,ParameterValue=your.domain. \
    ParameterKey=CodeshipIAMUser,ParameterValue=svc_codeship

Codeship Integration

More information on this can be found here:

https://blog.codeship.com/integrating-aws-lambda-with-codeship/

Note that to get this deploying with Codeship, you'll need to define the below environment variables:

AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY with the API key/secret for your Codeship IAM user
AWS_DEFAULT_REGION with the region you created the CloudFormation stack in
LAMBDA_FUNCTION with the contents of the Lambda output from the CloudFormation stack

Todo

get configuration from S3 instead
don't lookup the hosted zone info every invocation because that's yuk
optionally cache the DescribeInstance data in an Elasticache store for later use (such as by a related Lambda function that runs at instance termination...)

Notes

Codeship/structure based on the work of my awesome colleague, Nathan Humphreys. Thanks!

matthope/lambda-ec2-dns