fly-atc
A SaaS toolkit for converting a personal application into a efficient, siloed, multi-tenant application, where each user of your application is assigned a dedicated virtual machine.
** Work in Progress **
Usage
Quickstart (single tenant):
bundle add fly-atc bundle binstubs fly-atc
Replace thruster with fly-atc in Dockerfile.
Quickstart (multi-tenant):
bundle add fly-atc bin/rails generate atc
Edit config/atc.yml as needed.
For approximately $1 US per month, you can run:
- 1 performance machine with 2Gb of RAM, 10GB of bandwidth, and 5GB of storage for 15 hours/month.
- 1 shared machine with 1Gb of RAM, 10GB of bandwidth, and 5GB of storage for 80 hours/month.
Vertical scaling can be achieved by adding more machines.
Motivation
I’ve been running my Showcase software for nearly three years. Things have changed over time that I now want to take advantage of. I want take the opportunity to package those changes in the form of a toolkit that others can take advantage of.
From Wikipedia description of SaaS:
> SaaS customers have the abstraction of limitless computing resources, while economy of scale drives down the cost. SaaS architectures are typically multi-tenant; usually they share resources between clients for efficiency, but sometimes they offer a siloed environment for an additional fee.
The focus of this toolkit is efficient, siloed, multi-tenant applications with no changes to the application, taking advantage of:
- Auto-suspend - Virtual Machines that pop into existence when needed and disappear when not in use.
- SQLite ready for production - raw performance coupled with operational compression of complexity; see Supercharge the One Person Framework with SQLite: Rails World 2024.
- Litestream - No-worry backups. Virtual machines can be literally destroyed and recreated elsewhere and start back up exactly where they left off.
- Tigris Global Storage - globally caching, S3-compatible object storage.
That’s a lot of moving parts. I’ve documented my current architecture and published a blueprint.
The goal of fly-atc is to enable you configure multiple tenants and then not worry about this further, enabling you to focus on your application.
Approach
For illustrative purposes consider a SaaS Calender application implemented in Ruby on Rails using SQLite3 as the database. (My showcase application is a bit more involved than a calendar, but those details aren’t important).
Key concepts:
- Each user/customer has a primarly location, and is assigned a single machine near that location. Such machines can be accessed from anywhere, but have lower latency near that location.
- Each user can have multiple calendars. Each calendar is associated with a single tenant on the user’s machine. Each tenant consists a running instance of the web server application with one (or more) databases.
With that in mind, consider the following URL paths:
/bellevue/2025/winter//bellevue/2025/summer-medal-ball//bellevue/2025/summer-showcase//boston/2025/april//boston/2025/mini-comp//boston/2025/october//livermore/2025/the-music-of-prince//livermore/2025/james-bond//raleigh/2025/disney//raleigh/2025/in-house/
The first segment of the path identifies the user, and therefore the machine. The next two segments combined identify the tenant on that machine. This is but a subset of the planned showcases, you can see a full list or even a map (click on the arrows under the map to move to different continents).
fly-atc‘s responsibilities are to:
- Route requests to the correct machine
- Ensure databases are present/restored from backup
- Start/stop tenants as required
- Hand off requests to tenants
Rails 8 introduces thruster. fly-atc is a replacement for thruster:
- thruster requires no configuration, is limited to a single tenant.
- fly-atc enables multiple tenants, based on your configuration.
Implementation
Based on:
Near term plans:
- Remove certificate/https support
- Add launch on request / shutdown on idle
- Add fly-replay
On the radar:
- Support for targets other than fly.io.
- Support for platforms other than Rails, likely starting with Node, and focusing on popular ORMs: Prisma, TypeORM, and Sequelize.
- Dashboard. One should be able to deploy new users and make other configuration changes using only your cell phone. I do this today with my showcase application.