B3LB is based on the Django Python Web framework and is designed to work in large scale-out deployments with 100+ BigBlueButton nodes and high attendee join rates.



To scale for a huge number of attendees it is possible to:

  • scale-out the B3LB API frontends

  • scale-out the B3LB polling workers

  • scale-out your BBB nodes


  • multiple b3lb frontend instances

  • backend BBB node polling using Celery

  • extensive caching based on Redis

  • robust against high BBB node response times (i.e. due to ongoing DDoS attacks)

BBB Clustering

  • supports a high number of BBB nodes

  • different load balancing factors per cluster

  • load calculation by attendees, meetings and CPU load metrics

  • maintenance mode allows to disable BBB nodes gracefully

BBB Frontend API

  • deployed on ASGI with uvicorn

  • HTTP call-outs are implementated async using aiohttp

  • support API key rollover using a second secret

  • prebuild responses for expensive API calls (getMeetings)

  • limiting attendees or meetings per tenant

  • does not implement but blocks recording API calls


  • per-tenant API hostnames

  • start presentation injection

  • branding logo injection

  • multiple API secrets per tenant


  • simple health-check URL

  • simple json statistics URL

  • prometheus metrics URL

Load Calculation

To select a BBB node for new meetings B3LB calculates a load value for the BBB nodes. The BBB node with the lowest load value is choosen. The load is based on three metrics:

  • number of attendees

  • number of meetings

  • cpu utilization (base 10.000)

Each of the metrics is important for deciding where to spawn new meetings. The cpu utilization depends on the current load caused by running meetings and also respects external effects of the BBB nodes. The number of meetings is important since it is an indicator that more attendees may join and cause even more load in the future.

\[ \begin{align}\begin{aligned}\begin{split}\begin{array}{clc} \mathbf{\text{Metric}} & \mathbf{\text{Description}} & \mathbf{\text{Origin}} \\ cpu_{15s} & \text{cpu utilization in the last 15s} & \text{node} \\ cpu_{1m} & \text{cpu utilization in the last minute} & \text{node} \\ n_{atn} & \text{number of active attendees} & \text{node} \\ n_{mtg} & \text{number of active meetings} & \text{node} \\ \end{array}\end{split}\\\begin{split}\\ \\\end{split}\\\begin{split}\begin{array}{cclc} \mathbf{\text{Tunable}} & \mathbf{\text{Default}} & \mathbf{\text{Description}} & \mathbf{\text{Origin}} \\ cpu_{max} & 5.000 & \text{target max cpu utilization} & \text{cluster} \\ cpu_{order} & 6 & \text{order of the polynomial} & \text{cluster} \\ f_{atn} & 1 & \text{load factor for a single attendee} & \text{cluster} \\ f_{mtg} & 30 & \text{load factor for a single meeting} & \text{cluster} \\ \end{array}\end{split}\\\begin{split} \\ \\\end{split}\\load_{node} = f_{atn} * n_{atn} + f_{mtg} * n_{mtg} + \frac{cpu_{max}}{cpu_{order}} * \sum_{n=1}^{cpu_{order}} {\left[\frac{ \max {\left(cpu_{1m}, cpu_{15s}\right)} }{10.000}\right]}^{n}\end{aligned}\end{align} \]

The cpu utilization is reinforced to get a slow increase as long the cpu utilization is low and increases more and more steep. The following plot shows the load value for a BBB node depending on it’s CPU utilization (base 10.000) for different attendee and meeting counts.

(Source code, png, hires.png, pdf)


Tuning the polynomial order changes the load balancing to be more or less cpu load sensitive:

(Source code, png, hires.png, pdf)


Container Images

B3LB provides in three different docker image provided on Docker Hub and GitHub Packages. The images can be build from source using the provided Dockerfiles.


It is intentional that there are no b3lb:latest nor b3lb-static:latest image tags available. You should always pick a explicit version for your deployment.


This image contains the Django files of b3lb to run the ASGI application, Celery tasks and manamgenet CLI commands.

docker pull ibhde/b3lb:1.2.0
docker pull docker.pkg.github.com/de-ibh/b3lb/b3lb:1.2.0


Uses the Caddy webserver to provide static assets for the Django admin UI and can be used to publish per-tenant assets.

docker pull ibhde/b3lb-static:1.2.0
docker pull docker.pkg.github.com/de-ibh/b3lb/b3lb-static:1.2.0


This is the development build of b3lb using Djangos single threaded build-in webserver. You should never use this in production.

docker pull ibhde/b3lb-dev:latest
docker pull docker.pkg.github.com/de-ibh/b3lb/b3lb-dev:latest