cobras 2.3.3

A realtime messaging server using WebSockets and Redis.

General

Cobra is a realtime messaging server using Python3, WebSockets and Redis Streams. It was presented in great details during RedisConf 2019. Since then we've added history support which let cobra retain messages published to a channel that no-one is subscribed to. This makes it easier to blow up your systems through OOMs and fill your hard drives, but it makes cobra much more useful.

• slides
• youtube

Cobra has been used in production receiving heavy traffic for about a year. Since it was written in Python it was named after a snake as an hommage to a great programming language.

There are 4 operations that a client can execute against a cobra server: publish, subscribe, read and write. publish and subscribe are the 2 operations core to a group-chat. read and write are the typical operations that key value stores (such as memcached), or a python dictionnary provide.

• publish: send data to a channel, which will be broadcasted to anyone subscribed to that channel
• subscribe: receive events sent to a channel in real time.
• write: record some data (addressed by a key)
• read: retrieve data

News

Cobra is actively being developed, check out the changelog to know what's cooking.

Installation

With pip

pip install cobras

With docker

docker pull bsergean/cobra

For development

git clone <url>
cd cobra
python3 -m venv venv
source venv/bin/activate
make dev
make test

Usage

Cobra server and test clients

$ cobra
Usage: cobra [OPTIONS] COMMAND [ARGS]...

  Cobra is a realtime messaging server using Python3, WebSockets and Redis
  PubSub.

Options:
  --version  Show the version and exit.
  --help     Show this message and exit.

Commands:
  admin            Run admin commands.
  health           Health check
  init             Setup cobra
  monitor          Monitor cobra
  publish          Publish to a channel
  run              Run the cobra server
  redis_subscribe  Subscribe to a channel (with redis)
  subscribe        Subscribe to a channel
  secret           Generate secrets used for authentication...

To run the server use cobra run. You can run a health-check against the server with cobra health.

cobra health --url 'ws://jeanserge.com/v2?appkey=_health' --secret A5a3BdEfbc6Df5AAFFcadE7F9Dd7F17E --role health

bavarde

bavarde is a chat client that runs against the public cobra server. Bring up 2 terminals, runs the 2 commands below and start typing.

$ bavarde client
...

$ bavarde client --username bob
...

Setup

cobras init needs to be run once to generate an app configuration file, in ~/.cobra.yaml. That file contains all the roles, secrets and apps configured. Clients will use this data to authenticate.

To run in production you will need a redis (version > 5) instance. Here are environment variables that you will likely want to tweak, to connect to 2 redis instances (for scalabity), and to bind on 0.0.0.0 so that the internet can see your instance.

- name: COBRA_HOST
  value: 0.0.0.0
- name: COBRA_REDIS_URLS
  value: redis://redis1;redis://redis2

# config can be a path to a file
- name: COBRA_APPS_CONFIG_PATH
  value: /path/to/your/cobra.yaml

# config can be a blob of gziped + base64 data (if you do not want to mount volumes)
# Generate it with:
# `gzip -c ~/.cobra.yaml | base64`
- name: COBRA_APPS_CONFIG_CONTENT
  value: BIGBLOGOFDATA

Thank you

There would be no cobra without some other amazing open-source projects and tech. Here are 3 very remarkable ones.

• Python (and asyncio, one of the killer python3 feature !)
• Redis, the swiss army knife of the internet which provide a very scalable publish/subscribe feature to dispatch messages while retaining them and allowing lookups of old messages (see [Redis Streams] (https://redis.io/topics/streams-intro).
• The python websockets library, very elegantly implementing the WebSockets protocol using asyncio.
• The python aioredis library used to talk to Redis. This redis labs article explains some pitfalls with asyncio and how to get the best performance out of it.