How a Single 8 GB Server Powered 500 K Users for 15 Years – The Webminal Story

Origin

In 2010 a developer named Lakshmipathi wanted a real Linux shell that could be accessed directly from a web browser, avoiding the complexity of local installations and virtual‑machine setups. This idea led to the creation of Webminal, a free online Linux learning platform.

Infrastructure

Webminal runs on a single CentOS server with 8 GB of RAM. The architecture deliberately avoids container orchestration, clustering, and auto‑scaling. Since its launch in 2011 the core setup has remained unchanged, yet it has survived several major incidents:

2017: a Spanish tech blog drove a one‑day traffic surge of 10 000 users.

2021: a data‑center fire caused loss of 150 000 user accounts.

Multiple power‑outage events in the Netherlands caused temporary service interruptions.

Despite these challenges the service has accumulated more than 500 000 users over fifteen years.

Technical Stack

Language: Python 2.7

Web framework: Flask 0.12.5

Terminal emulator: Shellinabox (released 2005, unmaintained since 2017) – chosen for its ability to traverse firewalls and corporate networks.

Root environment: User Mode Linux (UML), a 2001 technology that runs a full Linux kernel in user space, providing each user with an isolated kernel instance.

Monitoring: eBPF/execsnoop – the only modern component, used to capture live command execution streams.

Database: MySQL, running on the same physical server.

Front‑end: Plain HTML with inline CSS (no React, Vue, npm).

Why Not Docker?

The platform’s tutorials require low‑level operations such as fdisk, LVM management, RAID configuration, and filesystem creation ( mkfs). These commands need genuine block devices, which Docker cannot provide without substantial additional complexity. UML supplies real block devices, making it a better fit for the educational goals.

UML Implementation Details

Each user receives a separate UML instance – effectively a full Linux kernel – with four virtual block devices (each 64 MB) for practicing LVM, RAID, and partitioning. An instance runs with 256 MB of RAM and shares a copy‑on‑write (COW) base image, keeping storage overhead low: 100 concurrent users add only about 2 GB of extra storage.

$ screen -x chat</code>
<code>$ cat > /dev/null</code>
<code>hey, should we add MySQL support?

When a user types poweroff, the UML instance exits cleanly, returning to the host shell with zero risk.

Real‑Time Command Stream

Using eBPF, Webminal captures live command execution from all active users, anonymises the data (removing parameters, paths, and passwords), and displays a scrolling command feed on the homepage. To date the feed has recorded over 2.8 million commands.

Attempts at Modernisation

The team briefly replaced Shellinabox with a WebSocket‑based terminal, but the new solution caused browser compatibility problems (e.g., white screens in Firefox) after only a few hours, leading to a revert to Shellinabox.

Funding and Sustainability

Webminal carries no advertisements, no venture‑capital funding, and no paid subscription features. All server costs are paid out‑of‑pocket by the founder. In 2023 a GitHub Sponsors page was opened to raise funds for upgrading the server memory from 8 GB to 128 GB, aiming to increase concurrency for the root environment.

Reference

https://community.webminal.org/t/15-years-one-server-8gb-ram-and-500k-users-how-webminal-refuses-to-die/8803