sample-helper-aws-appconfig 1.1.0

Sample helper library for AWS AppConfig

Sample AWS AppConfig Helper

A sample helper Python library for AWS AppConfig which makes rolling configuration updates out easier.

Features

• Configurable update interval: you can ask the library to update your configuration as often as needed, but it will only call the AWS AppConfig API at the configured interval (in seconds).
• Uses best practices for updates: the API is called with the version of the last received configuration, which results in a lower charge for the API call if no new configuration has been deployed. Automatically generates a client ID if you do not specify one.
• Flexible: Can automatically fetch the current configuration on initialisation, every time the configuration is read by your code, or on demand. You can override the caching interval if needed.
• Handles YAML, JSON and plain text configurations, stored in any supported AppConfig store. Any other content type is returned unprocessed as the Python bytes type.
• Supports AWS Lambda, Amazon EC2 instances and on-premises use.

Installation

pip install sample-helper-aws-appconfig

Example

from appconfig_helper import AppConfigHelper
from fastapi import FastAPI

appconfig = AppConfigHelper(
    "MyAppConfigApp",
    "MyAppConfigEnvironment",
    "MyAppConfigProfile",
    45  # minimum interval between update checks
)

app = FastAPI()

@app.get("/some-url")
def index():
    if appconfig.update_config():
        print("New configuration received")
    # your configuration is available in the "config" attribute
    return {
        "config_info": appconfig.config
    }

Usage

Please see the AWS AppConfig documentation for details on configuring the service.

Initialising

Start by creating an AppConfigHelper object. You must specify the application name, environment name, and profile (configuration) name. You must also specify the refresh interval, in seconds. AppConfigHelper will not attempt to fetch a new configuration version from the AWS AppConfig service more frequently than this interval. You should set it low enough that your code will receive new configuration promptly, but not so low that it takes too long. The library enforces a minimum interval of 15 seconds.

The configuration is not automatically fetched unless you set fetch_on_init. To have the library fetch the configuration when it is accessed, if it has been more than max_config_age seconds since the last fetch, set fetch_on_read.

If you need to customise the AWS credentials or region, set session to a configured boto3.Session object. Otherwise, the standard boto3 logic for credential/configuration discovery is used.

AWS AppConfig needs clients to specify a unique client ID to allow deployment strategies to work correctly. The library will automatically use the hostname, but you can override it with client_id. (The specific value does not matter, but it should be different for each client, and should not change.)

Reading the configuration

The configuration from AWS AppConfig is available as the config property. Before accessing it, you should call update_config(), unless you specified fetch_on_init or fetch_on_read during initialisation. If you want to force a config fetch, even if the number of seconds specified have not yet passed, call update_config(True).

update_config() returns True if a new version of the configuration was received. If no attempt was made to fetch it, or the configuration received was the same as current one, it returns False. It will raise ValueError if the received configuration data could not be processed (e.g. invalid JSON). If needed, the inner exception for JSON or YAML parsing is available as __context__ on the raised exception.

To read the values in your configuration, access the config property. For JSON and YAML configurations, this will contain the structure of your data. For plain text configurations, this will be a simple string.

The original data received from AppConfig is available in the raw_config property. Accessing this property will not trigger an automatic update even if fetch_on_read is True. The content type field received from AppConfig is available in the content_type property.

For example, with the following JSON in your AppConfig configuration profile:

{
    "hello": "world",
    "data": {
        "is_sample": true
    }
}

you would see the following when using the library:

# appconfig is the instance of the library
>>> appconfig.config["hello"]
"world"
>>> appconfig.config["data"]
{'is_sample': True}

You can check which version of the configuration was last received by examining the config_version property. Note that this value is opaque and depends on the service being used to store the configuration data. For example, if Amazon S3 is being used, then the version will be the version identifier of the object, not an integer.

Use in AWS Lambda

AWS AppConfig is best used in Lambda by taking advantage of Lambda Extensions

Security

See CONTRIBUTING for more information.

Licence

This library is licensed under Apache-2.0. See the LICENSE file.