Asyncio daemon tutorial

This tutorial shows how to build an asyncio daemon following the dependency injection principle.

In this tutorial we will use:

  • Python 3

  • Docker

  • Docker-compose

Start from the scratch or jump to the section:

You can find complete project on the Github.

What are we going to build?

We will build a monitoring daemon that monitors web services availability.

The daemon will send the requests to the example.com and httpbin.org every couple of seconds. For each successfully completed response it will log:

  • The response code

  • The amount of bytes in the response

  • The time took to complete the response

../_images/diagram.png

Prerequisites

We will use Docker and docker-compose in this tutorial. Let’s check the versions:

docker --version
docker-compose --version

The output should look something like:

Docker version 19.03.12, build 48a66213fe
docker-compose version 1.26.2, build eefe0d31

Note

If you don’t have Docker or docker-compose you need to install them before proceeding. Follow these installation guides:

The prerequisites are satisfied. Let’s get started with the project layout.

Project layout

Create the project root folder and set it as a working directory:

mkdir asyncio-daemon-tutorial
cd asyncio-daemon-tutorial

Now we need to create the initial project structure. Create the files and folders following next layout. All files should be empty for now. We will fill them later.

Initial project layout:

./
├── monitoringdaemon/
│   ├── __init__.py
│   ├── __main__.py
│   └── containers.py
├── config.yml
├── docker-compose.yml
├── Dockerfile
└── requirements.txt

Initial project layout is ready. We will extend it in the next sections.

Let’s proceed to the environment preparation.

Prepare the environment

In this section we are going to prepare the environment for running our daemon.

First we need to specify the project requirements. We will use next packages:

  • dependency-injector - the dependency injection framework

  • aiohttp - the web framework (we need only http client)

  • pyyaml - the YAML files parsing library, used for the reading of the configuration files

  • pytest - the test framework

  • pytest-asyncio - the helper library for the testing of the asyncio application

  • pytest-cov - the helper library for measuring the test coverage

Put next lines into the requirements.txt file:

dependency-injector
aiohttp
pyyaml
pytest
pytest-asyncio
pytest-cov

Second, we need to create the Dockerfile. It will describe the daemon’s build process and specify how to run it. We will use python:3.8-buster as a base image.

Put next lines into the Dockerfile file:

FROM python:3.8-buster

ENV PYTHONUNBUFFERED=1

WORKDIR /code
COPY . /code/

RUN apt-get install openssl \
 && pip install --upgrade pip \
 && pip install -r requirements.txt \
 && rm -rf ~/.cache

CMD ["python", "-m", "monitoringdaemon"]

Third, we need to define the container in the docker-compose configuration.

Put next lines into the docker-compose.yml file:

version: "3.7"

services:

  monitor:
    build: ./
    image: monitoring-daemon
    volumes:
      - "./:/code"

All is ready. Let’s check that the environment is setup properly.

Run in the terminal:

docker-compose build

The build process may take a couple of minutes. You should see something like this in the end:

Successfully built 5b4ee5e76e35
Successfully tagged monitoring-daemon:latest

After the build is done run the container:

docker-compose up

The output should look like:

Creating network "asyncio-daemon-tutorial_default" with the default driver
Creating asyncio-daemon-tutorial_monitor_1 ... done
Attaching to asyncio-daemon-tutorial_monitor_1
asyncio-daemon-tutorial_monitor_1 exited with code 0

The environment is ready. The application does not do any work and just exits with a code 0.

Next step is to configure the logging and configuration file parsing.

Logging and configuration

In this section we will configure the logging and configuration file parsing.

Let’s start with the the main part of our application - the container. Container will keep all of the application components and their dependencies.

First two components that we’re going to add are the config object and the provider for configuring the logging.

Put next lines into the containers.py file:

"""Containers module."""

import logging
import sys

from dependency_injector import containers, providers


class Container(containers.DeclarativeContainer):

    config = providers.Configuration()

    logging = providers.Resource(
        logging.basicConfig,
        stream=sys.stdout,
        level=config.log.level,
        format=config.log.format,
    )

Note

We have used the configuration value before it was defined. That’s the principle how the Configuration provider works.

Use first, define later.

The configuration file will keep the logging settings.

Put next lines into the config.yml file:

log:
  level: "INFO"
  format: "[%(asctime)s] [%(levelname)s] [%(name)s]: %(message)s"

Now let’s create the function that will run our daemon. It’s traditionally called main(). The main() function will create the container. Then it will use the container to parse the config.yml file and call the logging configuration provider.

Put next lines into the __main__.py file:

"""Main module."""

from .containers import Container


def main() -> None:
    ...


if __name__ == '__main__':
    container = Container()
    container.config.from_yaml('config.yml')
    container.init_resources()

    main()

Note

Container is the first object in the application.

Logging and configuration parsing part is done. In next section we will create the monitoring checks dispatcher.

Dispatcher

Now let’s add the monitoring checks dispatcher.

The dispatcher will control a list of the monitoring tasks. It will execute each task according to the configured schedule. The Monitor class is the base class for all the monitors. You can create different monitors by subclassing it and implementing the check() method.

../_images/classes-01.png

Let’s create dispatcher and the monitor base classes.

Create dispatcher.py and monitors.py in the monitoringdaemon package:

./
├── monitoringdaemon/
│   ├── __init__.py
│   ├── __main__.py
│   ├── containers.py
│   ├── dispatcher.py
│   └── monitors.py
├── config.yml
├── docker-compose.yml
├── Dockerfile
└── requirements.txt

Put next into the monitors.py:

"""Monitors module."""

import logging


class Monitor:

    def __init__(self, check_every: int) -> None:
        self.check_every = check_every
        self.logger = logging.getLogger(self.__class__.__name__)

    async def check(self) -> None:
        raise NotImplementedError()

and next into the dispatcher.py:

"""Dispatcher module."""

import asyncio
import logging
import signal
import time
from typing import List

from .monitors import Monitor


class Dispatcher:

    def __init__(self, monitors: List[Monitor]) -> None:
        self._monitors = monitors
        self._monitor_tasks: List[asyncio.Task] = []
        self._logger = logging.getLogger(self.__class__.__name__)
        self._stopping = False

    def run(self) -> None:
        asyncio.run(self.start())

    async def start(self) -> None:
        self._logger.info('Starting up')

        for monitor in self._monitors:
            self._monitor_tasks.append(
                asyncio.create_task(self._run_monitor(monitor)),
            )

        asyncio.get_event_loop().add_signal_handler(signal.SIGTERM, self.stop)
        asyncio.get_event_loop().add_signal_handler(signal.SIGINT, self.stop)

        await asyncio.gather(*self._monitor_tasks, return_exceptions=True)

        self.stop()

    def stop(self) -> None:
        if self._stopping:
            return

        self._stopping = True

        self._logger.info('Shutting down')
        for task, monitor in zip(self._monitor_tasks, self._monitors):
            task.cancel()
        self._monitor_tasks.clear()
        self._logger.info('Shutdown finished successfully')

    @staticmethod
    async def _run_monitor(monitor: Monitor) -> None:
        def _until_next(last: float) -> float:
            time_took = time.time() - last
            return monitor.check_every - time_took

        while True:
            time_start = time.time()

            try:
                await monitor.check()
            except asyncio.CancelledError:
                break
            except Exception:
                monitor.logger.exception('Error executing monitor check')

            await asyncio.sleep(_until_next(last=time_start))

Now we need to add the dispatcher to the container.

Edit containers.py:

"""Containers module."""

import logging
import sys

from dependency_injector import containers, providers

from . import dispatcher


class Container(containers.DeclarativeContainer):

    config = providers.Configuration()

    logging = providers.Resource(
        logging.basicConfig,
        stream=sys.stdout,
        level=config.log.level,
        format=config.log.format,
    )

    dispatcher = providers.Factory(
        dispatcher.Dispatcher,
        monitors=providers.List(
            # TODO: add monitors
        ),
    )

At the last we will inject dispatcher into the main() function and call the run() method. We will use Wiring feature.

Edit __main__.py:

"""Main module."""

import sys

from dependency_injector.wiring import inject, Provide

from .dispatcher import Dispatcher
from .containers import Container


@inject
def main(dispatcher: Dispatcher = Provide[Container.dispatcher]) -> None:
    dispatcher.run()


if __name__ == '__main__':
    container = Container()
    container.config.from_yaml('config.yml')
    container.init_resources()
    container.wire(modules=[sys.modules[__name__]])

    main()

Finally let’s start the daemon to check that all works.

Run in the terminal:

docker-compose up

The output should look like:

Starting asyncio-daemon-tutorial_monitor_1 ... done
Attaching to asyncio-daemon-tutorial_monitor_1
monitor_1  | [2020-08-08 16:12:35,772] [INFO] [Dispatcher]: Starting up
monitor_1  | [2020-08-08 16:12:35,774] [INFO] [Dispatcher]: Shutting down
monitor_1  | [2020-08-08 16:12:35,774] [INFO] [Dispatcher]: Shutdown finished successfully
asyncio-daemon-tutorial_monitor_1 exited with code 0

Everything works properly. Dispatcher starts up and exits because there are no monitoring tasks.

By the end of this section we have the application skeleton ready. In next section will will add first monitoring task.

Example.com monitor

In this section we will add a monitoring task that will check the availability of the http://example.com.

We will start from the extending of our class model with a new type of the monitoring check, the HttpMonitor.

The HttpMonitor is a subclass of the Monitor. We will implement the check() method that will send the HTTP request to the specified URL. The http request sending will be delegated to the HttpClient.

../_images/classes-02.png

First we need to create the HttpClient.

Create http.py in the monitoringdaemon package:

./
├── monitoringdaemon/
│   ├── __init__.py
│   ├── __main__.py
│   ├── containers.py
│   ├── dispatcher.py
│   ├── http.py
│   └── monitors.py
├── config.yml
├── docker-compose.yml
├── Dockerfile
└── requirements.txt

and put next into it:

"""Http client module."""

from aiohttp import ClientSession, ClientTimeout, ClientResponse


class HttpClient:

    async def request(self, method: str, url: str, timeout: int) -> ClientResponse:
        async with ClientSession(timeout=ClientTimeout(timeout)) as session:
            async with session.request(method, url) as response:
                return response

Now we need to add the HttpClient to the container.

Edit containers.py:

"""Containers module."""

import logging
import sys

from dependency_injector import containers, providers

from . import http, dispatcher


class Container(containers.DeclarativeContainer):

    config = providers.Configuration()

    logging = providers.Resource(
        logging.basicConfig,
        stream=sys.stdout,
        level=config.log.level,
        format=config.log.format,
    )

    http_client = providers.Factory(http.HttpClient)

    dispatcher = providers.Factory(
        dispatcher.Dispatcher,
        monitors=providers.List(
            # TODO: add monitors
        ),
    )

Now we’re ready to add the HttpMonitor. We will add it to the monitors module.

Edit monitors.py:

"""Monitors module."""

import logging
import time
from typing import Dict, Any

from .http import HttpClient


class Monitor:

    def __init__(self, check_every: int) -> None:
        self.check_every = check_every
        self.logger = logging.getLogger(self.__class__.__name__)

    async def check(self) -> None:
        raise NotImplementedError()


class HttpMonitor(Monitor):

    def __init__(
            self,
            http_client: HttpClient,
            options: Dict[str, Any],
    ) -> None:
        self._client = http_client
        self._method = options.pop('method')
        self._url = options.pop('url')
        self._timeout = options.pop('timeout')
        super().__init__(check_every=options.pop('check_every'))

    async def check(self) -> None:
        time_start = time.time()

        response = await self._client.request(
            method=self._method,
            url=self._url,
            timeout=self._timeout,
        )

        time_end = time.time()
        time_took = time_end - time_start

        self.logger.info(
            'Check\n'
            '    %s %s\n'
            '    response code: %s\n'
            '    content length: %s\n'
            '    request took: %s seconds',
            self._method,
            self._url,
            response.status,
            response.content_length,
            round(time_took, 3)
        )

We have everything ready to add the http://example.com monitoring check. We make two changes in the container:

  • Add the factory provider example_monitor.

  • Inject the example_monitor into the dispatcher.

Edit containers.py:

"""Containers module."""

import logging
import sys

from dependency_injector import containers, providers

from . import http, monitors, dispatcher


class Container(containers.DeclarativeContainer):

    config = providers.Configuration()

    logging = providers.Resource(
        logging.basicConfig,
        stream=sys.stdout,
        level=config.log.level,
        format=config.log.format,
    )

    http_client = providers.Factory(http.HttpClient)

    example_monitor = providers.Factory(
        monitors.HttpMonitor,
        http_client=http_client,
        options=config.monitors.example,
    )

    dispatcher = providers.Factory(
        dispatcher.Dispatcher,
        monitors=providers.List(
            example_monitor,
        ),
    )

Provider example_monitor has a dependency on the configuration options. Let’s define these options.

Edit config.yml:

log:
  level: "INFO"
  format: "[%(asctime)s] [%(levelname)s] [%(name)s]: %(message)s"

monitors:

  example:
    method: "GET"
    url: "http://example.com"
    timeout: 5
    check_every: 5

All set. Start the daemon to check that all works.

Run in the terminal:

docker-compose up

You should see:

Starting asyncio-daemon-tutorial_monitor_1 ... done
Attaching to asyncio-daemon-tutorial_monitor_1
monitor_1  | [2020-08-08 17:06:41,965] [INFO] [Dispatcher]: Starting up
monitor_1  | [2020-08-08 17:06:42,033] [INFO] [HttpMonitor]: Check
monitor_1  |     GET http://example.com
monitor_1  |     response code: 200
monitor_1  |     content length: 648
monitor_1  |     request took: 0.067 seconds
monitor_1  | [2020-08-08 17:06:47,040] [INFO] [HttpMonitor]: Check
monitor_1  |     GET http://example.com
monitor_1  |     response code: 200
monitor_1  |     content length: 648
monitor_1  |     request took: 0.073 seconds

Our daemon can monitor http://example.com availability.

Let’s add a monitor for the https://httpbin.org.

Httpbin.org monitor

Adding of a monitor for the https://httpbin.org will be much easier because we have all the components ready. We just need to create a new provider in the container and update the configuration.

Edit containers.py:

"""Containers module."""

import logging
import sys

from dependency_injector import containers, providers

from . import http, monitors, dispatcher


class Container(containers.DeclarativeContainer):

    config = providers.Configuration()

    logging = providers.Resource(
        logging.basicConfig,
        stream=sys.stdout,
        level=config.log.level,
        format=config.log.format,
    )

    http_client = providers.Factory(http.HttpClient)

    example_monitor = providers.Factory(
        monitors.HttpMonitor,
        http_client=http_client,
        options=config.monitors.example,
    )

    httpbin_monitor = providers.Factory(
        monitors.HttpMonitor,
        http_client=http_client,
        options=config.monitors.httpbin,
    )

    dispatcher = providers.Factory(
        dispatcher.Dispatcher,
        monitors=providers.List(
            example_monitor,
            httpbin_monitor,
        ),
    )

Edit config.yml:

log:
  level: "INFO"
  format: "[%(asctime)s] [%(levelname)s] [%(name)s]: %(message)s"

monitors:

  example:
    method: "GET"
    url: "http://example.com"
    timeout: 5
    check_every: 5

  httpbin:
    method: "GET"
    url: "https://httpbin.org/get"
    timeout: 5
    check_every: 5

Let’s start the daemon and check the logs.

Run in the terminal:

docker-compose up

You should see:

Starting asyncio-daemon-tutorial_monitor_1 ... done
Attaching to asyncio-daemon-tutorial_monitor_1
monitor_1  | [2020-08-08 18:09:08,540] [INFO] [Dispatcher]: Starting up
monitor_1  | [2020-08-08 18:09:08,618] [INFO] [HttpMonitor]: Check
monitor_1  |     GET http://example.com
monitor_1  |     response code: 200
monitor_1  |     content length: 648
monitor_1  |     request took: 0.077 seconds
monitor_1  | [2020-08-08 18:09:08,722] [INFO] [HttpMonitor]: Check
monitor_1  |     GET https://httpbin.org/get
monitor_1  |     response code: 200
monitor_1  |     content length: 310
monitor_1  |     request took: 0.18 seconds
monitor_1  | [2020-08-08 18:09:13,619] [INFO] [HttpMonitor]: Check
monitor_1  |     GET http://example.com
monitor_1  |     response code: 200
monitor_1  |     content length: 648
monitor_1  |     request took: 0.066 seconds
monitor_1  | [2020-08-08 18:09:13,681] [INFO] [HttpMonitor]: Check
monitor_1  |     GET https://httpbin.org/get
monitor_1  |     response code: 200
monitor_1  |     content length: 310
monitor_1  |     request took: 0.126 seconds

The functional part is done. Daemon monitors http://example.com and https://httpbin.org.

In next section we will add some tests.

Tests

In this section we will add some tests.

We will use pytest and coverage.

Create tests.py in the monitoringdaemon package:

./
├── monitoringdaemon/
│   ├── __init__.py
│   ├── __main__.py
│   ├── containers.py
│   ├── dispatcher.py
│   ├── http.py
│   ├── monitors.py
│   └── tests.py
├── config.yml
├── docker-compose.yml
├── Dockerfile
└── requirements.txt

and put next into it:

"""Tests module."""

import asyncio
import dataclasses
from unittest import mock

import pytest

from .containers import Container


@dataclasses.dataclass
class RequestStub:
    status: int
    content_length: int


@pytest.fixture
def container():
    container = Container()
    container.config.from_dict({
        'log': {
            'level': 'INFO',
            'formant': '[%(asctime)s] [%(levelname)s] [%(name)s]: %(message)s',
        },
        'monitors': {
            'example': {
                'method': 'GET',
                'url': 'http://fake-example.com',
                'timeout': 1,
                'check_every': 1,
            },
            'httpbin': {
                'method': 'GET',
                'url': 'https://fake-httpbin.org/get',
                'timeout': 1,
                'check_every': 1,
            },
        },
    })
    return container


@pytest.mark.asyncio
async def test_example_monitor(container, caplog):
    caplog.set_level('INFO')

    http_client_mock = mock.AsyncMock()
    http_client_mock.request.return_value = RequestStub(
        status=200,
        content_length=635,
    )

    with container.http_client.override(http_client_mock):
        example_monitor = container.example_monitor()
        await example_monitor.check()

    assert 'http://fake-example.com' in caplog.text
    assert 'response code: 200' in caplog.text
    assert 'content length: 635' in caplog.text


@pytest.mark.asyncio
async def test_dispatcher(container, caplog, event_loop):
    caplog.set_level('INFO')

    example_monitor_mock = mock.AsyncMock()
    httpbin_monitor_mock = mock.AsyncMock()

    with container.example_monitor.override(example_monitor_mock), \
            container.httpbin_monitor.override(httpbin_monitor_mock):

        dispatcher = container.dispatcher()
        event_loop.create_task(dispatcher.start())
        await asyncio.sleep(0.1)
        dispatcher.stop()

    assert example_monitor_mock.check.called
    assert httpbin_monitor_mock.check.called

Run in the terminal:

docker-compose run --rm monitor py.test monitoringdaemon/tests.py --cov=monitoringdaemon

You should see:

platform linux -- Python 3.8.3, pytest-6.0.1, py-1.9.0, pluggy-0.13.1
rootdir: /code
plugins: asyncio-0.14.0, cov-2.10.0
collected 2 items

monitoringdaemon/tests.py ..                                    [100%]

----------- coverage: platform linux, python 3.8.3-final-0 -----------
Name                             Stmts   Miss  Cover
----------------------------------------------------
monitoringdaemon/__init__.py         0      0   100%
monitoringdaemon/__main__.py        13     13     0%
monitoringdaemon/containers.py      11      0   100%
monitoringdaemon/dispatcher.py      44      5    89%
monitoringdaemon/http.py             6      3    50%
monitoringdaemon/monitors.py        23      1    96%
monitoringdaemon/tests.py           37      0   100%
----------------------------------------------------
TOTAL                              134     22    84%

Note

Take a look at the highlights in the tests.py.

In the test_example_monitor it emphasizes the overriding of the HttpClient. The real HTTP calls are mocked.

In the test_dispatcher we override both monitors with the mocks.

Conclusion

In this tutorial we’ve built an asyncio monitoring daemon following the dependency injection principle. We’ve used the Dependency Injector as a dependency injection framework.

With a help of Containers and Providers we have defined how to assemble application components.

List provider helped to inject a list of monitors into dispatcher. Configuration provider helped to deal with reading YAML file.

We used Wiring feature to inject dispatcher into the main() function. Provider overriding feature helped in testing.

We kept all the dependencies injected explicitly. This will help when you need to add or change something in future.

You can find complete project on the Github.

What’s next?