Deploy to Render (Free Tier)

How to deploy the rollup server to Render so the WASM playground talks to a real, public backend instead of localhost:3000.

Why Render

Free hosting tiers compared:

For a learning/demo project that prioritizes “no credit card”, Render wins. The trade-off is no persistent disk on free tier — sled state is lost on cold start. We handle that by re-seeding default accounts on startup.

What’s Already Set Up

This repo includes:

• Dockerfile — multi-stage build, ~30MB final image
• .dockerignore — excludes target/, web/, docs/, etc. for faster build
• PORT env support — main.rs reads PORT env var (Render assigns one dynamically)
• DATA_DIR env support — sled storage path is configurable

Deploy Steps

1. Sign up at Render

render.com, no credit card required.

2. Connect GitHub repo

• Dashboard → New → Web Service
• Connect your GitHub account
• Select egpivo/rust-zkp

3. Configure

• Name: rust-zkp (or anything; this becomes part of your URL)
• Region: Oregon / Frankfurt / Singapore (closest to you)
• Branch: main
• Runtime: Docker (auto-detected from Dockerfile)
• Plan: Free
• Auto-Deploy: Yes (redeploys on every push to main)

Click Create Web Service.

4. Wait for first build (5-10 min)

Render runs:

1. docker build .
2. Boots a container
3. Maps your service to a public URL

You get a URL like https://rust-zkp.onrender.com.

5. Verify

curl https://rust-zkp.onrender.com/health
# expect: ok

curl https://rust-zkp.onrender.com/accounts
# expect: JSON array with seeded accounts

6. Update WASM playground

Edit web/src/pages/demos/send.astro, accounts.astro:

<input id="server" value="https://rust-zkp.onrender.com">

Push, and GitHub Pages auto-deploys with the new default URL. Users hitting your playground will talk to your hosted server out of the box.

What to Expect

• Cold start: 30-60s (free tier scales to zero after 15min idle)
• State: re-seeded on each cold start (no persistent disk)
• Logs: Render dashboard → service → Logs tab
• CORS: already enabled in main.rs, all browsers can hit it
• HTTPS: free, auto-provisioned via Let’s Encrypt
• Custom domain: free on Render (paid features start at custom regions / static IPs)

Limits to Know

For a low-traffic demo, this is plenty. If you outgrow it: move to Fly.io ($2-5/mo with persistent disk) or upgrade Render to $7/mo for always-on.

Common Pitfalls

1. “Failed to fetch” from browser

Likely CORS — but you’ve already configured Any origin, so this should work. If you hit issues:

• Open browser DevTools → Network tab
• Check the failing request’s Response Headers
• Make sure access-control-allow-origin: * is present

2. App is “spinning down” / slow first request

Cold start. Hit /health to wake it before testing other endpoints.

3. Logs show panic

docker run locally first to test:

docker build -t zkp .
docker run -p 3000:3000 zkp
curl http://localhost:3000/health

4. Build fails on Render

Common reasons:

• Cargo.lock missing (commit it)
• Dependencies need system libs (the Dockerfile installs pkg-config libssl-dev already)
• Free tier ran out of build minutes (check dashboard)

Rollback

If a deploy breaks:

• Render dashboard → Deploys tab
• Click any past deploy → Redeploy

That’s it.

Why No Persistent Disk on Free Tier

Render’s free tier doesn’t include persistent volumes. The container’s filesystem is ephemeral — anything written disappears on restart.

For our demo this means:

• Accounts created via POST /accounts survive within a session
• After 15min idle → container dies → state wiped
• Next request → cold start → re-seeds the 4 default accounts

If you need persistence on Render free, you’d either:

• Use Render PostgreSQL (free 90 days, then $7/mo)
• Upgrade to Render’s $7/mo tier with disk
• Move to Fly.io with persistent volumes

For learning purposes, ephemeral state is acceptable — the architecture is real, just the data isn’t durable.