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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.{your-region-here}/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": { "Fn:Join": [ "", ["https://s3.amazonaws.com/com.gilt.public.backoffice", { "Ref": "AWS:Region" }, "/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"
  ]
}

Warning

If you update your helper stack, all client stacks (i.e. other stacks that use the helpers) will be okay after the new version is deployed. But some helpers rely on stored data to do the delete when the client stack is deleted. This is stored in a DynamoDB table and will get blown away when you delete-then-recreate the helper stack. You can get around this by updating the stack instead of tearing it down and recreating it. But it's probably a good idea to export the helper's DynamoDB table so you have a backup. If you lose the data, when you tear down client stacks, you may have to manually delete some resources created by the helpers.

A note on AWS Regions

At times, AWS can be touchy when it comes to referencing resources across regions. With that in mind, this project is replicated to all regions - so you simply need to reference the version that lives in the S3 bucket that corresponds to the region you're working in. If there is a new region that is not part of the ring of replications, please create an issue.

Steps for adding a new included function

  1. Find the file to edit.
    • If a file already exists for the AWS service in the aws directory, add the code there.
    • If not, create a new file for the AWS service.
  2. Implement the function
    • Add a new class that implements base.Handler for the new functionality. In most cases, it will be sufficient to pass all parameters (other than ServiceToken through to the AWS client).
    • If the 'delete' can't be implemented using the 'create' parameters, make sure the 'create' returns all necessary data needed for the 'delete' (such as unknowable ids); these will be stored in DynamoDB for future reference in the 'delete'.
  3. Add a new export method that calls the new class.
  4. Add two new Resources to the create_cloudformation_helper_functions.template:
    • The Role for the new function.
    • The function itself (referencing the new method from #3).
  5. Add an output for the function ARN to the template.
  6. Add an example template to the test directory.
  7. Update the README to explain the new helper function.

Included functions

Create a full API in API Gateway

Pass in all of the components of the API endpoints, and the API will be created in API Gateway.

This will delete the entire API when the corresponding stack is deleted.

Parameters

name

The name of the API, seen in the list of APIs in AWS Console.

description

The description of what the API does.

endpoints

A JSON array of (see the example template below for a working example):

  {
    "resource": {
      "sub-resource": {
        "GET": {
          "authorizationType": "NONE",
          "integration": {
            "type": "MOCK",
            "contentType": "text/html"
          }
        }
      },
      "POST": {
        "authorizationType": "NONE",
        "integration": {
          "type": "AWS",
          "integrationHttpMethod": "POST",
          "uri": "arn:aws:apigateway:us-east-1:lambda:path/2015-03-31/functions/arn:aws:lambda:*:*:function:your-function-name/invocations",
          "contentType": "application/json"
        }
      }
    }
  }
  1. The properties of the JSON document are either a) the HTTP method or b) a sub-resource.
  2. The resources cannot include a '/' - any resources nested in the path should also be nested in the JSON document.
  3. The parameters of each http method object are the same as putMethod callh ere: http://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/APIGateway.html#putMethod-property - except that httpMethod, resourceId, and restApiId will be added for you.
  4. Each http method object can also optionally specify an "integration" property, which follows http://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/APIGateway.html#putIntegration-property with the same properties automatically filled in for you.
  5. The "integration" property must include a "contentType" property that specifies the response Content-Type of the endpoint.

Output

baseUrl

The base url of the API endpoints. Combine this with the relative paths defined in the config to put together the full url for the API call.

restApiId

The id of the API that is created.

Reference Output Name

ApiGatewayCreateApiFunction

Example/Test Template

apiGateway.createApi.template

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

Create a Kinesis stream

Mirrors the Kinesis.createStream API method. Yes, CloudFormation does support creating a Kinesis stream, but it does not allow you to specify the steam name; this helper does.

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

Parameters

ShardCount

The number of shards for the stream. Required; no default.

StreamName

The name of the stream. Required.

Output

StreamName and Arn (of the stream) - matches the output of the existing CloudFormation task.

Reference Output Name

KinesisCreateStreamFunctionArn

Example/Test Template

kinesis.createStream.template

Put CloudWatch Logs Metric Filter

Mirrors the CloudWatchLogs.putMetricFilter API method.

This will delete the metric filter when the corresponding stack is deleted.

Parameters

Exactly the same as the documentation above.

Reference Output Name

CloudWatchLogsPutMetricFilterFunctionArn

Example/Test Template

cloudWatchLogs.putMetricFilter.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

Put S3 Bucket Policy

Mirrors the S3.putBucketPolicy API method.

This will replace the existing policy if any is already configured.

Parameters

Bucket

The S3 bucket to put the policy

Policy

The policy to put (it is a string containing a JSON description of the policy. All quotes in the policy must hence be escaped)

Reference Output Name

S3PutBucketPolicyFunctionArn

Example/Test Template

s3.putBucketPolicy.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

Create a SES Receipt Rule

Allows to create an SES Receipt Rule inside an existing SES Rule set (active or not). Mirrors the SES.CreateReceipRule API method. This will delete the rule when the corresponding stack is deleted.

Paramters

See the reference above or the example below for full list of parameters. All parameters are directly passed 'as is' except boolean which are converted.

Reference Output Name

SesCreateReceiptRuleFunctionArn

Example/Test Template

ses.createReceiptRule.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.us-east-1/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.us-east-1/cloudformation_templates

License

Copyright 2016 Gilt Groupe, Inc.

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