Horizontal scaling

By horizontal scaling, we mean that you can run multiple instances of the vantage6 server simultaneously to handle a high workload. This is useful when a single machine running the server is no longer sufficient to handle all requests.

How it works

Horizontal scaling with vantage6 can be done using a RabbitMQ server. RabbitMQ is a widely used message broker. Below, we will first explain how we use RabbitMQ, and then discuss the implementation.

The websocket connection between server and nodes is used to process various changes in the network’s state. For example, a node can create a new (sub)task for the other nodes in the collaboration. The server then communicates these tasks via the socket connection. Now, if we use multiple instances of the central server, different nodes in the same collaboration may connect to different instances, and then, the server would not be able to deliver the new task properly. This is where RabbitMQ comes in.

When RabbitMQ is enabled, the websocket messages are directed over the RabbitMQ message queue, and delivered to the nodes regardless of which server instance they are connected to. The RabbitMQ service thus helps to ensure that all websocket events are still communicated properly to all involved parties.

How to use

If you use multiple server instances, you should always connect them to the same RabbitMQ instance. You can achieve this by adding your RabbitMQ server when you create a new server with vserver new, or you can add it later to your server configuration file with the flag rabbitmq_uri: <your URI>.

A RabbitMQ URI is set up in the following way:

amqp://$user:$password@$host:$port/$vhost

Where $user is the username, $password is the password, $host is the URL where your RabbitMQ service is running, $port is the queue’s port (which is 5672 if you are using the RabbitMQ Docker image), and $vhost is the name of your virtual host (you could e.g. run one instance group per vhost).

We recommend running the Docker implementation of RabbitMQ. Optionally, use the ‘management’ container that provides a user interface to manage your connections on port 15672.