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Cloud Custodian - Policy Rules Engine

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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

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

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.


- `Homepage <>`_
- `Docs <>`_
- `Developer Install <>`_
- `Presentations <>`_

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

You can run it with Docker as well
# Download the image
$ docker pull cloudcustodian/c7n

# Run the policy
$ docker run -it \
-v $(pwd)/output:/output \
-v $(pwd)/policy.yml:/policy.yml \
--env-file <(env | grep "^AWS") \
cloudcustodian/c7n run -v -s /output /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
* Reddit -
* Gitter -

Additional Tools

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

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


We welcome Your interest in Capital One’s Open Source Projects (the
“Project”). Any Contributor to the Project must accept and sign an
Agreement indicating agreement to the license terms below. Except for
the license granted in this Agreement to Capital One and to recipients
of software distributed by Capital One, You reserve all right, title,
and interest in and to Your Contributions; this Agreement does not
impact Your rights to use Your own Contributions for any other purpose.

`Sign the Individual Agreement <>`_

`Sign the Corporate Agreement <>`_

Code of Conduct

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

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