confd

Confd is an open-source configuration management tool that keeps local configuration files in sync with data stored in centralized key-value stores such as etcd and Consul. It renders configuration files from templates using values pulled from the backend and updates the files when the backend data changes. Confd is designed for dynamic environments where services frequently reconfigure at runtime, such as containerized or cloud deployments.

Confd operates as a small daemon. It reads a set of TOML configuration files located in a conf.d directory, with each entry describing a single template to process. Each template specifies a source template file, a destination path, and the keys to fetch from the backend. Templates use Go's template syntax with helper functions to retrieve values. When confd detects a change in the configured keys, it re-renders the template and writes the updated content to the destination file. It can also trigger a reload command for the associated service after writing.

Backends supported include etcd and Consul, enabling templates to pull values from these centralized stores. Deployment typically places templates under /etc/confd/templates and the corresponding conf.d definitions under /etc/confd/conf.d.

Confd originated in the ecosystem around CoreOS and early container-oriented deployments and remains in use in some infrastructure stacks to decouple application configuration from image pipelines. It provides a lightweight mechanism for dynamic configuration without requiring more heavyweight configuration management systems.