Cloud Custodian is an open-source rules engine for managing cloud environments. Policies are written in a YAML-based language that finds, filters, tags and acts on resources. This supports cloud security, cost optimisation and governance, for example tag compliance, cleaning up unused resources and switching systems off outside office hours. It works with AWS, Azure and GCP, and can run locally, on an instance, as a Docker container or serverless in AWS Lambda.
The project is licensed under Apache 2.0 and is an incubating project of the Cloud Native Computing Foundation, part of the Linux Foundation, whose legal address is in San Francisco. There is no vendor-hosted service: you run the software in your own environment, so policies and logs stay under your own control. The cloud accounts it manages do sit with the supported providers, which include US hyperscalers. For a European organisation the open licence is the main point of interest: the code can be inspected, adapted and used independently of a single vendor.