Flask Management Endpoints

Flask Management Endpoints allows for the definition of endpoints in your Flask application such that Kubernetes can use them for liveness and readiness probes. Additionally, it provides verbose health and informational endpoints. The API is designed in the style of Spring Actuator management endpoints.

Endpoint	Method / Return Type	Description
/info	GET / json	Provides information about the application and host system.
/health	GET / json	Runs all health checks and outputs the status of each health check.
/health/liveness	GET / json	Returns successfully if endpoint is running with terse output.
/health/ping	GET / json	Returns successfully if endpoint is running with terse output (same as liveness).
/health/readiness	GET / json	Readiness probe endpoint that can run dependent checks, but is the same as liveness by default.
/version	GET / plaintext	By default returns the contents of the environment variable VERSION, but can be configured to return any value via a closure.

Configuration

To register the Flask Blueprint in your application:

from flask import Flask
from flask_management_endpoints import z_blueprint

app = Flask(__name__)
app.register_blueprint(z_blueprint)

If you would like to mount the endpoint at a different URL prefix than the default (/z), then it can be specified when registering the blueprint:

app.register_blueprint(z_blueprint, url_prefix="/admin")

Next, define the URL service health checks that you would like to register. The service dependencies can be defined as a fixed URL in which checks will be appended to the end. Alternatively, dependencies can be defined with simply a hostname and an optional port, then the URL scheme and paths will be filled in by defaults.

app.config.update(
    Z_ENDPOINTS={        
        "service_dependencies": {
            # key is an identifier for the service name
            # value is a base URL pointing to a Spring Actuator style health endpoint or just a hostname with
            # an optional port.
            'users_api': 'https://user-service:9922/admin', # readiness check: https://user-service:9922/admin/readiness
            'widget_api': 'widget-service', # readiness check: {PREFERRED_URL_SCHEME}://widget-service/{url_prefix}/health/readiness
        }
    }
)

If you would like to have custom functions that will execute on the on a given check (health, readiness, version, etc), you can define them as follows.

def db_check():
    try:
        engine = users_db.engine
        result = engine.execute('SELECT 1')
        return result.first()[0] == 1
    except Exception as err:
        app.logger.error(f'DB health check failed: {err}')
        return False

app.config.update(
    Z_ENDPOINTS={
        'check_functions': {
            'health': {
                'db': db_check
            }
        }
    }

Extension

This project can also be used via the provided Flask extension. With the extension the blueprint is registered using the ManagementEndpoints class.

from flask import Flask
from flask_management_endpoints import ManagementEndpoints

app = Flask(__name__)
ManagementEndpoints(app)

The rest of the configuration is identical.

The extension has an additional option, no_log, that can disable logging of the HTTP requests handled by your healthz endpoints, to avoid cluttering your web log files with automated requests. At the moment, only the gunicorn web server is supported.

ManagementEndpoints(app, no_log=True)

Other Resources

If you need a less opinionated Flask health check blueprint, check out flask-healthz.

License

Copyright 2021 Elijah Zupancic

The Flask Management Endpoints project is licensed under the same license as Flask itself: BSD 3-clause.