cloudformation-helpers

A collection of AWS Lambda funtions that fill in the gaps that existing CloudFormation resources do not cover.

AWS CloudFormation supports Custom Resources (http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/template-custom-resources.html), which can be used to call AWS Lambda functions. CloudFormation covers much of the AWS API landscape, but does leave some gaps unsupported. AWS Lambda can contain any sort of logic, including interacting with the AWS API in ways not covered by CloudFormation. By combining the two, CloudFormation deploys should be able to approach the full resource support given by the AWS API.

Warning: most of these functions require fairly wide permissions, since they need access to resources in a general manner - much the same way CloudFormation itself has permission to do almost anything.

Usage

1. Use https://s3.amazonaws.com/com.gilt.public.backoffice/cloudformation_templates/create_cloudformation_helper_functions.template to deploy a stack that creates the Lambda functions for you. Remember the stack name.

2. Include the following resources in your CloudFormation template. These will create a) a nested stack that looks up the ARNs from the previous step and b) a custom resource that allows your template to read those ARNs.

   "CFHelperStack": {
     "Type": "AWS::CloudFormation::Stack",
     "Properties": {
       "TemplateURL": "https://s3.amazonaws.com/com.gilt.public.backoffice/cloudformation_templates/lookup_stack_outputs.template"
     }
   },
   "CFHelper": {
     "Type": "Custom::CFHelper",
     "Properties": {
       "ServiceToken": { "Fn::GetAtt" : ["CFHelperStack", "Outputs.LookupStackOutputsArn"] },
       "StackName": "your-helper-stack-name-here"
     },
     "DependsOn": [
       "CFHelperStack"
     ]
   }
   

   You can either hardcode the stack name of your helper functions, or request it as a parameter.

3. Use the ARNs from the previous step in a custom resource, to call those Lambda functions:

   "PopulateTable": {
     "Type": "Custom::PopulateTable",
     "Properties": {
       "ServiceToken": { "Fn::GetAtt" : ["CFHelper", "DynamoDBPutItemsFunctionArn"] },
       "TableName": "your-table-name",
       "Items": [
         {
           "key": "foo1",
           "value": {
             "bar": 1.5,
             "baz": "qwerty"
           }
         },
         {
           "key": "foo2",
           "value": false
         }
       ]
     },
     "DependsOn": [
       "CFHelper"
     ]
   }
   

Included functions

Insert items into DynamoDB

Pass in a list of items to be inserted into a DynamoDB table. This is useful to provide a template for the content of the table, or to populate a config table. There is no data-checking, so it is up to the client to ensure that the format of the data is correct.

Warning: it is a PUT, so it will overwrite any items that already exist for the table's primary key.

This will delete the items when the corresponding stack is deleted.

Parameters

TableName

The name of the DynamoDB table to insert into. Must exist at the time of the insert, i.e. will not create if it does not already exist.

Items

A JSON array of items to be inserted, in JSON format (not DynamoDB format).

Output

The list of TableName/Key pairs of items created.

Reference Output Name

DynamoDBPutItemsFunctionArn

Example/Test Template

dynamo.putItems.template

Put S3 Objects

Mirrors the S3.putObject API method.

This will delete the objects and any added sub-objects (for "folders") when the corresponding stack is deleted.

Parameters

Bucket

The S3 bucket to put the object into

Key

The name of the object. Can include a "path" for organization in S3.

Body

The content of the object being put into S3 (a string).

Other

Please see the reference above for further parameters - these are only the most commonly-used ones.

Output

The result of the S3.PutObject API method.

Reference Output Name

S3PutObjectFunctionArn

Example/Test Template

s3.putObject.template

Subscribe to SNS topics

Mirrors the SNS.Subscribe API method. To be used when the SNS topic already exists (since CloudFormation allows subscriptions to be created when creating SNS topics only).

This will delete the subscription when the corresponding stack is deleted.

Parameters

Endpoint

The endpoint that receives the SNS messages.

Protocol

The type of endpoint. Can be one of the following values: application, email, email-json, http, https, lambda, sms, sqs.

TopicArn

The SNS topic to subscribe to.

Output

The result of the SNS.Subscribe API method, i.e. SubscriptionArn

Reference Output Name

SnsSubscribeFunctionArn

Example/Test Template

sns.subscribe.template

Deployment (contributors)

After making changes (i.e. adding a new helper function), please do the following:

1. Upload this zipped repo to the com.gilt.public.backoffice/lambda_functions bucket. To produce the .zip file:

     zip -r cloudformation-helpers.zip . -x *.git* -x *cloudformation-helpers.zip*
   

   Unfortunately we can't use the Github .zip file directly, because it zips the code into a subdirectory named after the repo; AWS Lambda then can't find the .js file containing the helper functions because it is not on the top-level.

2. Upload the edited create_cloudformation_helper_functions.template to com.gilt.public.backoffice/cloudformation_templates

License

Copyright 2016 Gilt Groupe, Inc.

Licensed under the Apache License, Version 2.0: http://www.apache.org/licenses/LICENSE-2.0