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CFN Teardown

Cleanup CloudFormation stacks respecting the order of dependencies.

Features

Install

Download binary for the appropriate platform from HERE.

✗ wget -q https://github.com/nirdosh17/cfn-teardown/releases/download/v1.0.0/cfn-teardown_Linux_x86_64.tar.gz
✗ tar -xzf cfn-teardown_Linux_x86_64.tar.gz
✗ touch ~/.cfn-teardown.yaml 

✗ ./cfn-teardown version
Using config file:  /Users/nirdosh/.cfn-teardown.yaml
Version:  v1.0.0

Usage

Required global flags for all commands: STACK_PATTERN, AWS_REGION, AWS_PROFILE

  1. Run cfn-teardown -h and see available commands and needed parameters.

  2. Listing stack dependencies: cfn-teardown listDependencies

    Generates dependencies in stack_teardown_details.json file (printed in terminal as well)

  3. Tear down stacks: cfn-teardown deleteStacks

    Deletes matching stacks and updates status in the teardown details file as the script is running.

Selecting Stacks For Deletion

For stacks with consistent naming convention:

Let's say you have stacks starting with the environment name followed by a hyphen:

In this can, you need to set stack pattern as ^qa- to match stacks starting with qa-.

For stacks which do not follow any naming pattern:

Example:

Use the root stack's name as the stack pattern i.e. ^qa-shared-networks. The script will find out all dependendent stacks from the root stack recursively until the leaf nodes have zero importer stacks.

Configuration

Configuration for this command can be set in three different ways in the precedence order defined below:

  1. Environment variables(same as flag name)

  2. Flags e.g. cfn-teardown deleteStacks --STACK_PATTERN=qaenv-

  3. Supplied YAML Config file (default: ~/.cfn-teardown.yaml)

    <details> <summary><b>Minimal config file</b></summary> 
    AWS_REGION: us-east-1
AWS_PROFILE: staging
STACK_PATTERN: qa-
    </details> <details> <summary><b>All configs present</b></summary> 
    AWS_REGION: us-east-1
AWS_PROFILE: staging
TARGET_ACCOUNT_ID: 121212121212
STACK_PATTERN: qa-
ABORT_WAIT_TIME_MINUTES: 20
STACK_WAIT_TIME_SECONDS: 30
MAX_DELETE_RETRY_COUNT: 5
SLACK_WEBHOOK_URL: https://hooks.slack.com/services/dummy/dummy/long_hash
ROLE_ARN: "<arn>"
DRY_RUN: "false"
    </details>

See available configurations via: cfn-teardown <command> --help

Stack Teardown Strategy

  1. Find matching stacks based on the regex provided

  2. Prepare stack dependencies

    <details> <summary><b>It looks something like this:</b></summary> 
    {
  "staging-bucket-archived-items": {
    "StackName": "staging-bucket-archived-items",
    "Status": "CREATE_COMPLETE",
    "StackStatusReason": "",
    "DeleteStartedAt": "2021-02-07T03:35:43Z",
    "DeleteCompletedAt": "",
    "DeletionTimeInMinutes": "",
    "DeleteAttempt": 0,
    "Exports": [
      "staging:ItemsArchiveBucket",
      "staging:ItemsArchiveBucketArn"
    ],
    "ActiveImporterStacks": {
      "staging-products-service": {}
    },
    "CFNConsoleLink": "https://console.aws.amazon.com/cloudformation/home?region=us-east-1#/stacks/stackinfo?stackId=staging-bucket-archived-items"
  },
  "staging-products-service": {
    "StackName": "staging-products-service",
    "Status": "CREATE_COMPLETE",
    "StackStatusReason": "",
    "DeleteStartedAt": "2021-02-07T03:30:54Z",
    "DeleteCompletedAt": "",
    "DeletionTimeInMinutes": "",
    "DeleteAttempt": 0,
    "Exports": [
      "staging:ProductsServiceEndpoint"
    ],
    "ActiveImporterStacks": {},
    "CFNConsoleLink": "https://console.aws.amazon.com/cloudformation/home?region=us-east-1#/stacks/stackinfo?stackId=staging-products-service"
  }
}
    </details>

  3. Alert slack channel(if provided) and waits before initiating deletion. Starts deletion immediately if no wait time is provided.

  4. Select stacks which are eligible for deletion. A stack is eligible for deletion if it's exports are imported by no other stacks. In simple terms, it should have no dependencies.

  5. Send delete requests for all selected stacks.

  6. Wait for 30 seconds(configurable) before scanning eligible stacks again. Checks If the stack has been already deleted and if deleted updates stack status in the dependency tree.

  7. This process (sending delete requests, waiting, checking stack status) is repeated until all stacks have status DELETE_COMPLETE.

  8. If a stack is not deleted even after exhausting all retries(default 5), teardown is halted and manual intervention is requested.

AWS Credentials

Only AWS profile based authentication supported at the moment. By default, it tries to use the IAM role of the caller but we can also supply role arn if we want the script to assume a different role.

Safety Flags

Limitation

If a stack can't be deleted from the AWS Console itself due to some dependencies or some error, then it won't be deleted by this tool as well. In such case, manual intervention is required.

Demo

<details><summary><strong>Deleting Stacks</strong></summary> <img src="https://user-images.githubusercontent.com/5920689/130366139-30912d09-7d79-4537-8809-014c75ce38c0.gif" width="600" alt="deleting stacks" />
<details><summary><strong>Slack Notifications</strong></summary> <img src="https://user-images.githubusercontent.com/5920689/130365254-dd2d911d-803b-4c02-93ec-2f78badedb6a.png" width="600" alt="slack notifications sample" />

Caution :warning:

With great power, comes great responsibility