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Fenrir is a secure AWS SAM deployer that can help manage your own serverless projects or scale serverless to a large organization. At its core it is a reimplementation of the sam deploy command as an AWS Step Function, so it's a serverless serverless (serverless^2) deployer. Fenrir also:

  1. Uses consistent naming: good naming (and tagging) of resources, like Lambda and API Gateway, will keep accounts clean and make obvious which resources belong to which projects.
  2. Follows recommended security practices: e.g. practice "least privilege" by giving Lambdas separate security groups and IAM roles.
  3. Creates a reliable workflow: cleanly handle failure in a way that shows what happened, why it happened, and how to remedy.
  4. Records what is deployed: quickly answering what is currently deployed allows engineers to debug and understand the current state of the world.

The goal is to provide a secure and pleasant experience for building and deploying serverless applications that can be used by a single developer or a large organisation.

Getting Started

Deploy Fenrir to AWS using ./scripts/cf_bootstrap <s3_bucket>. This creates a CloudFormation stack with the Fenrir Step Function, Lambdas, Buckets and Roles fenrir needs to run.

You can then cd examples/hello and fenrir package && fenrir deploy which will deploy the hello example application.

Hello application

Fenrir supports a subset of AWS SAM templates with only the addition of adding ProjectName and ConfigName to the top of the template.

The hello application template.yml looks like:

ProjectName: "coinbase/deploy-test"
ConfigName: "development"

AWSTemplateFormatVersion: "2010-09-09"
Transform: AWS::Serverless-2016-10-31

    Type: AWS::Serverless::Api
      StageName: dev
      EndpointConfiguration: REGIONAL
    Type: AWS::Serverless::Function
      CodeUri: .
      Role: lambda-role
      Handler: hello.lambda
      Runtime: go1.x
          Type: Api
            RestApiId: !Ref helloAPI
            Path: /hello
            Method: GET

With code that looks like:

package main

import (

func main() {
	lambda.Start(func(_ interface{}) (interface{}, error) {
		return map[string]string{"body": "Hello"}, nil

The name of the lambda function is hello so Fenrir expects the file / to exist in the built docker conatiner by having a Dockerfile:

FROM golang
RUN apt-get update && apt-get upgrade -y && apt-get install -y zip

COPY . .
RUN go get
RUN GOOS=linux GOARCH=amd64 go build -o hello.lambda .
RUN zip hello.lambda

With these in place you can now execute:

  • go build -o hello.lambda . && sam local start-api to start a local test API
  • fenrir package to prepare the files needed to deploy
  • fenrir deploy to deploy the template (requires fenrir deployer)

Supported Resources

Fenrir does not support all SAM resources or all properties. Generally it limits all references resources (e.g. Security Groups, Subnets, S3, Kinesis) to have specific tags AND it forces good naming patterns to stop conflicts.

The specific resources that it supports, and their limitations are:


  1. FunctionName is generated and cannot be defined.
  2. VPCConfig.SecurityGroupIds Each SG must have the ProjectName, ConfigName same as the template, and ServiceName equal to the name of the Lambda resource.
  3. VPCConfig.SubnetIds must have the DeployWithFenrir tag equal to true.
  4. Role must have the tags ProjectName, ConfigName same as the template, and ServiceName equal to the name of the Lambda resource.
  5. PermissionsBoundary must be defined, is defaulted to fenrir-permissions-boundary, must have correct tags (TODO for now it is hard coded as default)
  6. Policies only supports a list of SAM Policy templates of type (w/ limitations):
  7. DynamoDBCrudPolicy where TableName must be a local !Ref
  8. SQSPollerPolicy where QueueName must be a local !Ref
  9. LambdaInvokePolicy where FunctionName must be a local !Ref
  10. KMSDecryptPolicy where ref'd KeyId (can be alias) must have correct tags
  11. VPCAccessPolicy
  12. Events supported Types and their limitations are:
    1. Api: It must have RestApiId that is a reference to a local API resource
    2. S3: Bucket must have correct tags*
    3. CloudWatchLogs: LogGroupName must have correct tags*
    4. Kinesis: Stream must have correct tags*
    5. DynamoDB: Stream must have correct tags*
    6. SQS: Queue must have correct tags*
    7. SNS: Topic can be topic name or ARN and must have correct tags*
    8. Schedule
    9. CloudWatchEvent

*: correct tags means tags are FenrirAllAllowed=true OR have FenrirAllowed:<project>:<config>=true OR ProjectName and ConfigName tags equal to the release.


The limitations are:

  1. Name is generated and cannot be defined
  2. EndpointConfiguration defaults to PRIVATE


The limitations are:

  1. LayerName is generated and cannot be defined


  1. TableName is generated and cannot be defined
  2. DeletionPolicy is defaulted to Retain


  1. QueueName is generated and cannot be defined
  2. DeletionPolicy is defaulted to Retain

Fenrir Deployer

Fenrir is a Bifrost Step Function reimplemetnation of aws cloudformation deploy script. The logic flow looks like:

state diagram


There is always more to do:

  1. Auto add common sense Outputs
  2. S3 Static site uploader
  3. Support Role Arns and Name Tags
  4. Layers should not include environment e.g. development, just configuration to be the same ARN across accounts
  5. Layers should be able to reference "latest" version
  6. Let Fenrir Bootstrap itself by letting it deploy Step Functions

More Links

Links I have found useful:

API gateway resource policy:

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