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WebSocket Cluster (Spring Cloud) in action

This is a Spring Cloud project for WebSocket cluster servers.

中文

Principle

Using a consistent hashing algorithm, we construct a hash ring where the gateway listens to the up and down event of the WebSocket service instances and dynamically updates the hash ring according to the changes of the instances. Each time a new service comes online, the corresponding virtual node is added, and the WebSocket clients that need to change are reconnected to the new instance. Clients that need to be changed are reconnected to the new instance, which is the least expensive; of course, it also depends on the count of the virtual nodes and the fairness of the hashing algorithm. When the service goes offline, it is easier -- just disconnect all clients from the current instance, and the clients will always reconnect. At the same time, the core role of the hash ring is reflected in the load balancing. When the gateway does its request forwarding, it goes through our rewritten custom load balancing filter, which implements real node routing based on the fields that need to be hashed for business purposes.

Middleware / Environment Preparation

  • Docker (with API accessible)
  • Redis
  • RabbitMQ
  • Nacos

Development

Create a docker-compose network for docker-compose.yml:

docker network create compose-network

Local build and deploy by docker-compose:

mvn clean
mvn install -pl gateway -am -amd
mvn install -pl websocket -am -amd
docker build -t websocket:1.0.0 websocket/.
docker build -t gateway:1.0.0 gateway/.
docker-compose up -d
docker ps

Scale the websocket instance by: docker-compose scale websocket-server=3. Actually, I wrote a front-end web page to start a new instance for websocket service.

Don't forget to enable the docker remote api (e.g., check out docker -H tcp://0.0.0.0:2375 ps): The following steps may help:

Access docker API on Linux

Append -H tcp://0.0.0.0:2375 to the line started of ExecStart in the file named docker.service

# cat /usr/lib/systemd/system/docker.service
ExecStart=...... -H tcp://0.0.0.0:2375
# after saved, restart the docker process
systemctl daemon-reload
systemctl restart docker

Access docker API on macOS

The best practice is using the image alpine/socat to expose a tcp socket. ( see: usage of socat).

docker run -itd --name socat \
    -p 0.0.0.0:6666:2375 \
    -v /var/run/docker.sock:/var/run/docker.sock \
    alpine/socat \
    tcp-listen:2375,fork,reuseaddr unix-connect:/var/run/docker.sock

For the record, the Docker-desktop client for macOS provides the docker.for.mac.host.internal hostname for accessing the host in the container of docker. I also add this domain to my /etc/hosts and point it to the localhost address. So I use this address in application.yml to set up configuration for the redis, the rabbitmq and the nacos servers(they are all deployed in the container). You can change this address if you deploy on your machine or other linux servers. BTW, the Makefile is only for self usage, which makes me build and restart the service faster during the development phase because I didn't prepare a CI/CD pipeline for this project. Please use it as needed.

Front-end

Check out this react app. It looks like:

Demo

Contribution

If this project helps, please star it. Submit an issue if you have any question. You can contribute code by forking this project and submit your Pull Request.