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cloudformation-operator

A Kubernetes operator for managing CloudFormation stacks via kubectl and a custom resource definition.

Warning: this project is in alpha state. It should only be used to try out the demo and get the general idea.

This version uses the new operator-sdk. It's untested and may not work correctly

Deploy to a cluster

You need API access to a cluster running at least Kubernetes v1.17.0+.

Start the CloudFormation operator in your cluster by using the provided manifests:

$ make deploy IMG=quay.io/linki/cloudformation-operator:latest

Modify the region flag to match your cluster's.

Additionally you need to make sure that the operator Pod has enough AWS IAM permissions to create, update and delete CloudFormation stacks as well as permission to modify any resources that are part of the CloudFormation stacks you intend to deploy. In order to follow the example below it needs access to CloudFormation as well as S3.

The operator will require an IAM role or user credentials. Use the following Policy document as a guideline in order to follow the tutorial:

MyIAMRole:
  Properties:
    ...
    Policies:
    - PolicyDocument:
        Statement:
        - {Action: 'cloudformation:*', Effect: Allow, Resource: '*'}
        - {Action: 's3:*', Effect: Allow, Resource: '*'}
        Version: '2012-10-17'
    ...

The operator will usually use the IAM role of the EC2 instance it's running on, so you have to add those permissions to that role. If you're using Kube2IAM or similar and give your Pod a dedicated IAM role then you have to add the permissions to that role.

Once running the operator should print some output but shouldn't actually do anything at this point. Leave it running, keep watching its logs and continue with the steps below.

Demo

Create stack

Currently you don't have any stacks.

$ kubectl get stacks
No resources found.

Let's create a simple one that manages an S3 bucket:

apiVersion: cloudformation.linki.space/v1alpha1
kind: Stack
metadata:
  name: my-bucket
spec:
  template: |
    ---
    AWSTemplateFormatVersion: '2010-09-09'

    Resources:
      S3Bucket:
        Type: AWS::S3::Bucket
        Properties:
          VersioningConfiguration:
            Status: Suspended

The Stack resource's definition looks a lot like any other Kubernetes resource manifest. The spec section describes an attribute called template which contains a regular CloudFormation template.

Go ahead and submit the stack definition to your cluster:

$ kubectl apply -f config/samples/cfs-my-bucket-v1.yaml
stack "my-bucket" created
$ kubectl get stacks
NAME        AGE
my-bucket   21s

Open your AWS CloudFormation console and find your new stack.

Create stack

Once the CloudFormation stack is created check that your S3 bucket was created as well.

The operator will write back additional information about the CloudFormation Stack to your Kubernetes resource's status section, e.g. the stackID:

$ kubectl get stacks my-bucket -o yaml
spec:
  template:
  ...
status:
  stackID: arn:aws:cloudformation:eu-central-1:123456789012:stack/my-bucket/327b7d3c-f27b-4b94-8d17-92a1d9da85ab

Voilà, you just created a CloudFormation stack by only talking to Kubernetes.

Update stack

You can also update your stack: Let's change the VersioningConfiguration from Suspended to Enabled:

apiVersion: cloudformation.linki.space/v1alpha1
kind: Stack
metadata:
  name: my-bucket
spec:
  template: |
    ---
    AWSTemplateFormatVersion: '2010-09-09'

    Resources:
      S3Bucket:
        Type: AWS::S3::Bucket
        Properties:
          VersioningConfiguration:
            Status: Enabled

As with most Kubernetes resources you can update your Stack resource by applying a changed manifest to your Kubernetes cluster or by using kubectl edit stack my-stack.

$ kubectl apply -f config/samples/cfs-my-bucket-v2.yaml
stack "my-bucket" configured

Wait until the operator discovered and executed the change, then look at your AWS CloudFormation console again and find your stack being updated, yay.

Update stack

Tags

You may want to assign tags to your CloudFormation stacks. The tags added to a CloudFormation stack will be propagated to the managed resources. This feature may be useful in multiple cases, for example, to distinguish resources at billing report. Current operator provides two ways to assign tags:

apiVersion: cloudformation.linki.space/v1alpha1
kind: Stack
metadata:
  name: my-bucket
spec:
  tags:
    foo: dataFromStack
  template: |
    ---
    AWSTemplateFormatVersion: '2010-09-09'

    Resources:
      S3Bucket:
        Type: AWS::S3::Bucket
        Properties:
          VersioningConfiguration:
            Status: Enabled

Resource-specific tags have precedence over the default tags. Thus if a tag is defined at command-line arguments and for a Stack resource, the value from the Stack resource will be used.

If we run the operation and a Stack resource with the described above examples, we'll see such picture:

Stack tags

Parameters

However, often you'll want to extract dynamic values out of your CloudFormation stack template into so called Parameters so that your template itself doesn't change that often and, well, is really a template.

Let's extract the VersioningConfiguration into a parameter:

apiVersion: cloudformation.linki.space/v1alpha1
kind: Stack
metadata:
  name: my-bucket
spec:
  parameters:
    VersioningConfiguration: Enabled
  template: |
    ---
    AWSTemplateFormatVersion: '2010-09-09'

    Parameters:
      VersioningConfiguration:
        Type: String
        Default: none
        AllowedValues:
        - "Enabled"
        - "Suspended"

    Resources:
      S3Bucket:
        Type: AWS::S3::Bucket
        Properties:
          VersioningConfiguration:
            Status:
              Ref: VersioningConfiguration

and apply it to your cluster:

$ kubectl apply -f config/samples/cfs-my-bucket-v3.yaml
stack "my-bucket" configured

Since we changed the template a little this will update your CloudFormation stack. However, since we didn't actually change anything because we injected the same VersioningConfiguration value as before, your S3 bucket shouldn't change.

Any CloudFormation parameters defined in the CloudFormation template can be specified in the Stack resource's spec.parameters section. It's a simple key/value map.

Outputs

Furthermore, CloudFormation supports so called Outputs. These can be used for dynamic values that are only known after a stack has been created. In our example, we don't define a particular S3 bucket name but instead let AWS generate one for us.

Let's change our CloudFormation template to expose the generated bucket name via an Output:

apiVersion: cloudformation.linki.space/v1alpha1
kind: Stack
metadata:
  name: my-bucket
spec:
  parameters:
    VersioningConfiguration: Enabled
  template: |
    ---
    AWSTemplateFormatVersion: '2010-09-09'

    Parameters:
      VersioningConfiguration:
        Type: String
        Default: none
        AllowedValues:
        - "Enabled"
        - "Suspended"

    Resources:
      S3Bucket:
        Type: AWS::S3::Bucket
        Properties:
          VersioningConfiguration:
            Status:
              Ref: VersioningConfiguration

    Outputs:
      BucketName:
        Value: !Ref 'S3Bucket'
        Description: Name of the sample Amazon S3 bucket.

Apply the change to our cluster and wait until the operator has successfully updated the CloudFormation stack.

$ kubectl apply -f config/samples/cfs-my-bucket-v4.yaml
stack "my-bucket" configured

Every Output you define will be available in your Kubernetes resource's status section under the outputs field as a key/value map.

Let's check the name of our S3 bucket:

$ kubectl get stacks my-bucket -o yaml
spec:
  template:
  ...
status:
  stackID: ...
  outputs:
    BucketName: my-bucket-s3bucket-tarusnslfnsj

In the template we defined an Output called BucketName that should contain the name of our bucket after stack creation. Looking up the corresponding value under .status.outputs[BucketName] reveals that our bucket was named my-bucket-s3bucket-tarusnslfnsj.

Delete stack

The operator captures the whole lifecycle of a CloudFormation stack. So if you delete the resource from Kubernetes, the operator will teardown the CloudFormation stack as well. Let's do that now:

$ kubectl delete stack my-bucket
stack "my-bucket" deleted

Check your CloudFormation console once more and validate that your stack as well as your S3 bucket were deleted.

Delete stack

Command-line arguments

ArgumentEnvironment variableDefault valueDescription
assume-roleAssume AWS role when defined. Useful for stacks in another AWS account. Specify the full ARN, e.g. arn:aws:iam::123456789:role/cloudformation-operator
capabilityEnable specified capabilities for all stacks managed by the operator instance. Current parameter can be used multiple times. For example: --capability CAPABILITY_NAMED_IAM --capability CAPABILITY_IAM. Or with a line break when specifying as an environment variable: AWS_CAPABILITIES=CAPABILITY_IAM$'\n'CAPABILITY_NAMED_IAM
dry-runIf true, don't actually do anything.
tag ...Default tags which should be applied for all stacks. The format is --tag=foo=bar --tag=wambo=baz on the command line or with a line break when specifying as an env var. (e.g. in zsh: AWS_TAGS="foo=bar"$'\n'"wambo=baz")
namespaceWATCH_NAMESPACEdefaultThe Kubernetes namespace to watch
regionThe AWS region to use

Cleanup

Clean up the resources:

$ make undeploy

Build and run locally

This project uses the operator sdk.

$ make
$ WATCH_NAMESPACE=default KUBERNETES_CONFIG=~/.kube/config make run OPERATOR_FLAGS="--region eu-central-1"

Build the docker image

$ make docker-build quay.io/linki/cloudformation-operator:latest
$ make docker-push quay.io/linki/cloudformation-operator:latest

Test it locally

You can use OPERATOR_FLAGS to pass in flags using the operator-sdk.

Assuming you are using minikube:

$ minikube start # you will be have a kubeconfig read to use by cloudformation operator
$ export AWS_PROFILE=my_profile # setup your aws config
$ cd $GOPATH/src/github.com/linki/cloudformation-operator
$ # run cloudformation operator based on previous settings and env vars
$ WATCH_NAMESPACE=staging make run OPERATOR_FLAGS="--dry-run=true --region=eu-central-1"
I0122 16:31:14.509064  195514 request.go:645] Throttling request took 1.027790903s, request: GET:https://api.crc.testing:6443/apis/template.openshift.io/v1?timeout=32s
2021-01-22T16:31:15.863-0500    INFO    controller-runtime.metrics      metrics server is starting to listen    {"addr": ":8080"}
2021-01-22T16:31:15.864-0500    INFO    setup   
2021-01-22T16:31:15.864-0500    INFO    setup   starting manager
2021-01-22T16:31:15.864-0500    INFO    controller-runtime.manager      starting metrics server {"path": "/metrics"}
2021-01-22T16:31:15.864-0500    INFO    controller-runtime.manager.controller.stack     Starting EventSource    {"reconciler group": "cloudformation.linki.space", "reconciler kind": "Stack", "source": "kind source: /, Kind="}
2021-01-22T16:31:15.965-0500    INFO    controller-runtime.manager.controller.stack     Starting Controller     {"reconciler group": "cloudformation.linki.space", "reconciler kind": "Stack"}
2021-01-22T16:31:15.965-0500    INFO    controller-runtime.manager.controller.stack     Starting workers        {"reconciler group": "cloudformation.linki.space", "reconciler kind": "Stack", "worker count": 1}