SnapJoust: Photo Competitions Decided Head to Head

At work I have been running photo competitions once a quarter or so for about a year now. The process was simple:

1. People uploaded their photos to a Google Form.
2. I downloaded them all and stripped anything that gave away who took them¹.
3. I passed the lot to the previous winner, who picked their favourite.
4. The winner of this round picked the next theme and took over as the judge.
5. …
6. Do it all again.

It worked, and people enjoyed it, especially as work was happy to sponsor prizes, but it had a few problems. It was more manual faff for me than I wanted, and the result came down to one person’s taste. Win once and your out of the running for the next comp, which isn’t exactly fun.

So I built SnapJoust, a web app for running photo competitions where everyone gets a say, and the winner is decided by head-to-head voting².

How It Works

Someone sets up a competition with a theme, and one or more prompts: the questions voters answer, like “which photo has better composition?”. People submit their photos, and once the entries are approved, voting opens.

Voting is the “fun” bit. You’re shown two photos side by side and you pick the one you prefer. Then you get another pair, and another, through a set number of duels, skipping any pair you can’t decide on. You’re never shown a pair that includes one of your own photos³, and you can’t vote on the same pair twice⁴.

The pairs aren’t completely random. They’re weighted towards photos that haven’t been compared much yet⁵, so every entry gets a fair look rather than a couple of eye-catching ones hogging all the matchups.

When the competition closes (or earlier, if the organiser wants live results) there’s a ranking and a podium. SnapJoust can also generate a results image to post in a chat channel or anywhere else outside the app.

Why Head to Head?

Asking “which of these two is better?” is a much easier question than “rate this from 1 to 10”. Everyone’s 7 means something different, some people never give anything below a 5, and by the twentieth photo you’ve lost track of what your scores meant in the first place.

Picking between two is quick, it’s hard to get wrong, and it’s surprisingly addictive. Fewer tired voters means more votes, and more votes means a ranking you can actually trust.

The ranking is worked out from all those head-to-head results, either by simply counting wins or with an Elo-style win rate⁶. There’s also an optional “one prize per person” rule for the podium, so one prolific photographer can’t take gold, silver and bronze.

I’ve built quite a lot of flexibility into setting up the competitions, for example whether people can see other people’s entries before the voting starts⁷.

The Tech Stack

It’s a SvelteKit app (Svelte 5) running on Bun⁸, with PostgreSQL accessed through Drizzle ORM. If that sounds familiar, it’s very close to BooMap, just with a bigger database.

Sign-in is Better Auth again⁹, this time with email and password, Google, two-factor authentication and anonymous guest logins.

Guest mode is switched off for now though. The idea was that you could enter photos or vote without signing up, and later upgrade your account, but in practice it just confused people. They’d enter or vote as a guest, then sign in properly and wonder where their entries and votes had gone, or not realise they were a guest at all. It’s still in the code, so it can come back once I’ve worked out how to make it obvious what’s going on.

There is an admin system that I use for controlling some features and getting data out of the system. If the site ever gets popular, I think I’ll need to expand this to have other levels of admin.

Photos are resized on the server¹⁰ with sharp into thumbnail, 1080p and 4K WebP versions, with EXIF rotation sorted out along the way. They live in S3-compatible storage (MinIO in development), but they’re never served straight from the bucket; everything goes through the app¹¹. Storage is optional too: without it configured, the app just carries on without uploads.

It all runs on AWS ECS Fargate as a single long-lived server, not serverless functions. That choice turned out to shape a lot of what came next.

Waking a Sleeping Database

The database is Aurora Serverless, which can pause itself when nobody’s using it. That’s great for the bill on a site that sits idle between competitions, less great when the first visitor of the morning waits several seconds for it to wake up.

Rather than make people stare at a blank page, the app uses stale-while-revalidate. Pages that look the same for every anonymous visitor, like the competition list or public results, are kept in a plain in-memory LRU cache¹². If the database is asleep, you get the cached version straight away with a “stale” flag, and the page quietly polls in the background and swaps in fresh data once the database answers.

Anything that depends on who you are is never cached¹³. For those pages the app races the session lookup against a timeout. If the database is too slow, you get a placeholder straight away and the real content fills in when it arrives.

No Load Balancer

The usual way to put a container on the internet in AWS is a load balancer in front of it. SnapJoust doesn’t have one. Instead, a Cloudflare Tunnel runs as a sidecar container next to the app and connects outwards to Cloudflare, which sends visitors down the tunnel. This is mostly to save money.

It also means the service’s security group has no inbound rules at all. There’s nothing listening for the internet to find¹⁴. And it gives zero-downtime deploys almost for free: the new task’s tunnel joins as a second replica, and the old task only drains once the new one is taking traffic.

Thanks

A big thanks to Paul (of sticker fame) for testing SnapJoust and breaking it in more ways than I thought possible. Every time I told him something was finished, he found a new way to prove it wasn’t.

What’s Next

• Bring guest mode back, once it’s clear to people what being a guest actually means.
• Settle on a sensible set of default competition options, after a few more rounds.
• More levels of admin, if the site ever gets popular enough to need them.
• Maybe move off Bun, depending on how the drama shakes out.

Give It a Go

The work competitions are much less effort for me now. I set up the competition and approve the entries, and everyone else does the judging, two photos at a time. Everyone gets a say instead of one judge, and nobody has to wait for me to anonymise a folder of JPEGs.

If you run photo competitions at work, at a club, or just with friends, have a look at SnapJoust. And if you find a way to break it, you’re in good company.