flexi-settings 1.0.1.dev270004741

Manages embedded variables and blending settings

Library for handling variable resolution in scalars found within strings and “tree”-like data such as dict (internally), JSON/YAML content.

Note

This is a Python 3 only library. There is no support for Python 2.x.

Overview

This is to support YAML settings files that may have embedded variable references in scalar values that reference keys found within the same, or other content.

ROOT_DIR: "/var/log/my_project"

LOG_FILENAME: "!ROOT_DIR!/my_log_file.log"

The use-cases for this include:

• Reducing redundancy in YAML data

• Support for “local overrides” to replace some data at run-time

• Support for tests where the content is changed (overloaded) for unit tests

Features

This library provides a number of features including:

• A TreeData class for easily loading files from JSON/YAML or from native dict objects

• Visitor base classes for inspecting/manipulating the tree data

• Support for specifying primary content, overload content, and variable content

• Both variable resolution at load time and dynamically at run-time

• A set of standard “resolvers”

Resolvers

The library includes a set of standard resolvers. New resolvers can be defined easily by extending the Resolver base class.

• TreeDataResolver - Resolution from a TreeData (dict) object/YAML files

• DockerSwarmResolver - Resolution from Docker swarm configs/secrets

• EnvVarResolver - Resolve from environment variables

Visitors

The library includes a set of visitors for inspecting and updating TreeData objects.

Library Usage

A service (both standard “system-d” and container services) may use this to handle settings.

Overview

The settings are accessed via the ServiceSettings (or custom, extended class) Singleton. The specifics of what actors are involved in providing the settings are specified within a SettingsContext instance. These include the location of the primary settings file (generally a YAML file), the location of an optional override settings file, and the inclusion of resolvers for environment variables, Docker swarm secrets/configs, and any other optional resolvers (such as pulling settings from a database).

Startup Sequence

One of the first steps that a service should perform is creating an instance of the SettingsContext object. This instance is passed into the ServiceSettings and provides contextual details for loading the settings and resolving variables.