Load balancing#

Setting up load balancing is a huge topic, dependent on the precise system you are using, so the example below will be very generic. In most cases you set up a reverse proxy (like NGINX) to distribute the load across multiple application servers. If you are using a system like Kubernetes, it will also handle spinning up and shutting down the servers for you, and can even do so dynamically, depending on the amount of concurrent users to ensure that you are not wasting resources when there are fewer users, and / or when there is less computing demand.

Load balancing is the most complex approach to set up but is guaranteed to improve concurrent usage of your application since different users are not contending for access to the same process or even necessarily the same physical compute and memory resources. At the same time it is more wasteful of resources since it potentially occupies multiple machines and since each process is isolated there is no sharing of cached data or global state.

To get started configuring a load balancer take a look at the Bokeh documentation.

Use NGINX and Containers with Panel along with other Bokeh extensions#

Panel is built on top of Bokeh and uses the Bokeh server to serve applications. To serve Panel-specific resources, Panel is defined as a Bokeh extension. While Panel’s resources are available via a CDN, other Bokeh extensions may require being served directly by the Bokeh server. To enable this, set the BOKEH_RESOURCES environment variable to server.

An example is given below with ipywidget_bokeh as a Bokeh extension - but this will also work for other Bokeh extensions.

Files#

app.py

import ipywidgets
import panel as pn

pn.Row(ipywidgets.HTML("This is an IPywidget served with Panel")).servable()

Containerfile

FROM ubuntu:latest

# Linux Packages
RUN apt-get update && \
    apt-get install -y build-essential wget nginx && \
    apt-get clean && \
    rm -rf /var/lib/apt/lists/*

# Python Packages
ENV CONDA_DIR /opt/conda
RUN wget --quiet https://github.com/conda-forge/miniforge/releases/latest/download/Miniforge3-Linux-x86_64.sh -O ~/conda.sh && \
    /bin/bash ~/conda.sh -b -p $CONDA_DIR && rm ~/conda.sh
ENV PATH=$CONDA_DIR/bin:$PATH
RUN conda install python ipywidgets ipywidgets_bokeh panel -y

# Bokeh
ENV BOKEH_RESOURCES server
ENV BOKEH_ALLOW_WS_ORIGIN localhost

# Nginx
RUN rm /etc/nginx/sites-available/default
COPY nginx.conf /etc/nginx/sites-available/default

# App
COPY app.py .
COPY panel-serve.sh .
RUN chmod +x panel-serve.sh
WORKDIR /
CMD ["/bin/bash", "panel-serve.sh"]

panel-serve.sh

#!/bin/bash

nginx

# Serve the panel apps
panel serve app.py --port 5100 &
panel serve app.py --port 5101 &
panel serve app.py --port 5102 &

# Never stop
wait -n

nginx.conf

upstream app {
    # Should match what is defined in panel-serve.sh
    least_conn;
    server 127.0.0.1:5100;
    server 127.0.0.1:5101;
    server 127.0.0.1:5102;
}

server {
    listen 80 default_server;
    server_name _;

    access_log /tmp/bokeh.access.log;
    error_log /tmp/bokeh.error.log debug;

    location = /proxy {
        return 301 http://$http_host/proxy/;
    }

    location /proxy/ {
        rewrite ^/proxy/(.*)$ /$1 break;
        proxy_pass http://app/;

        proxy_set_header Host $host:$server_port;
        proxy_set_header X-Real-IP $remote_addr;
    }

    location ~ ^/proxy/(.*)/ws$ {
        rewrite ^/proxy/(.*)/ws$ /$1/ws break;
        proxy_pass http://app;

        proxy_http_version 1.1;
        proxy_set_header Connection "Upgrade";
        proxy_set_header Host $host:$server_port;
        proxy_set_header Upgrade $http_upgrade;
    }
}

Launching the app#

You can use any container framework to run the app. The commands below are for Podman, but you can use Docker as well. First, build the container with podman build -t my-container . and the run it podman run -dt -p 8000:80 localhost/my-container