Rules engine for cloud security, cost optimization, and governance, DSL in yaml for policies to query, filter, and take actions on resources
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Cloud Custodian

Cloud Custodian is a rules engine for managing public cloud accounts and resources. It allows users to define policies to enable a well managed cloud infrastructure, that's both secure and cost optimized. It consolidates many of the adhoc scripts organizations have into a lightweight and flexible tool, with unified metrics and reporting.

Custodian can be used to manage AWS, Azure, and GCP environments by ensuring real time compliance to security policies (like encryption and access requirements), tag policies, and cost management via garbage collection of unused resources and off-hours resource management.

Custodian policies are written in simple YAML configuration files that enable users to specify policies on a resource type (EC2, ASG, Redshift, CosmosDB, PubSub Topic) and are constructed from a vocabulary of filters and actions.

It integrates with the cloud native serverless capabilities of each provider to provide for real time enforcement of policies with builtin provisioning. Or it can be run as a simple cron job on a server to execute against large existing fleets.

Engineering the Next Generation of Cloud Governance” by @drewfirment


  • Comprehensive support for public cloud services and resources with a rich library of actions and filters to build policies with.
  • Supports arbitrary filtering on resources with nested boolean conditions.
  • Dry run any policy to see what it would do.
  • Automatically provisions serverless functions and event sources ( AWS CloudWatchEvents, AWS Config Rules, Azure EventGrid, GCP AuditLog & Pub/Sub, etc)
  • Cloud provider native metrics outputs on resources that matched a policy
  • Structured outputs into cloud native object storage of which resources matched a policy.
  • Intelligent cache usage to minimize api calls.
  • Supports multi-account/subscription/project usage.
  • Battle-tested - in production on some very large cloud environments.


Quick Install

$ virtualenv --python=python2 custodian
$ source custodian/bin/activate
(custodian) $ pip install c7n


First a policy file needs to be created in YAML format, as an example:

- name: remediate-extant-keys
  description: |
    Scan through all s3 buckets in an account and ensure all objects
    are encrypted (default to AES256).
  resource: aws.s3
    - encrypt-keys

- name: ec2-require-non-public-and-encrypted-volumes
  resource: aws.ec2
  description: |
    Provision a lambda and cloud watch event target
    that looks at all new instances and terminates those with
    unencrypted volumes.
    type: cloudtrail
        - RunInstances
    - type: ebs
      key: Encrypted
      value: false
    - terminate

- name: tag-compliance
  resource: aws.ec2
  description: |
    Schedule a resource that does not meet tag compliance policies
    to be stopped in four days.
    - State.Name: running
    - "tag:Environment": absent
    - "tag:AppId": absent
    - or:
      - "tag:OwnerContact": absent
      - "tag:DeptID": absent
    - type: mark-for-op
      op: stop
      days: 4

Given that, you can run Cloud Custodian with:

# Validate the configuration (note this happens by default on run)
$ custodian validate policy.yml

# Dryrun on the policies (no actions executed) to see what resources
# match each policy.
$ custodian run --dryrun -s out policy.yml

# Run the policy
$ custodian run -s out policy.yml

Custodian supports a few other useful subcommands and options, including outputs to S3, Cloudwatch metrics, STS role assumption. Policies go together like Lego bricks with actions and filters.

Consult the documentation for additional information, or reach out on gitter.

Get Involved

Mailing List -!forum/cloud-custodian

Gitter -

Additional Tools

The Custodian project also develops and maintains a suite of additional tools here

Multi-account policy execution.
Git history as stream of logical policy changes.
Scale out s3 scanning.
A reference implementation of sending messages to users to notify them.
Cloudtrail indexing and timeseries generation for dashboarding.
Cloud watch log exporting to s3
Indexing of custodian metrics and outputs for dashboarding
Cloudwatch Log parsing for python tracebacks to integrate with


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Code of Conduct

This project adheres to the Open Code of Conduct. By participating, you are expected to honor this code.