SimplySync by Simply Finance

Self-Hosting a Sync Relay

You can run a SimplySync relay in your own Cloudflare account without learning how to manage a server. The relay gets a public workers.dev URL that works from anywhere.

Your relay URL does not need to be secret. SimplySync encrypts every sync event on the device before uploading it, and the relay never receives the owner's decryption key. Each owner is also protected by a private write capability derived from the recovery key.

SimplySync does not operate a hosted relay service. The source in this repository is the product boundary: the agent or command below deploys that source into your Cloudflare account.

#Easiest setup: ask an AI agent

Open this SimplySync repository in ChatGPT/Codex or Claude Code and say:

Host my own SimplySync relay.

The repository includes the same host-relay skill for both agents. It checks and installs local tooling, opens Cloudflare signup or OAuth when needed, creates D1 and R2, applies migrations, deploys the relay, verifies /health, and returns a verified URL to paste into your app's Relay URL setting.

The agent pauses only when Cloudflare requires you to enter a password, MFA, CAPTCHA, billing details, or accept terms. Enter those details directly in the Cloudflare page; never paste them into the chat.

You can also invoke it directly with Use $host-relay to host my own SimplySync relay.

The agent deploys the exact checked-out source. It does not fetch a template, publish a package, or depend on a separate relay repository. You do not need a domain, VPS, Docker, port forwarding, private networking, or a TLS certificate. Cloudflare provides HTTPS for the public relay address.

#One setup command from a selective clone

curl -fsSL https://raw.githubusercontent.com/simply-hq/simplysync/main/clone-simplysync.sh |
  sh -s -- relay-cloudflare simplysync-cloudflare-relay
cd simplysync-cloudflare-relay
bun install --no-save
bun run relay:cloudflare:setup

The selective clone contains only the Cloudflare relay and repository-level scripts. The final command authenticates, creates or reuses D1 and R2, applies migrations, deploys, and waits for /health to return {"ok":true} before it prints the relay URL.

#Check that it works

  1. Require the setup command to print Relay verified and the relay URL.
  2. Paste the URL into the first device's Relay URL field and sync a change.
  3. Restore the same recovery key on a second device, configure the same URL, and confirm the change appears there.
  4. Keep any previous relay data or configuration until this test succeeds. Do not call the new relay redundant until existing encrypted history has been pushed to it and the restore test passes.

#What Cloudflare creates

Resource Purpose
Worker Receives authenticated sync requests at your public relay URL.
D1 database Stores encrypted events and small routing metadata.
R2 bucket Stores encrypted attachment chunks.

The default relay includes per-IP and per-owner rate limits, request-size caps, an owner-count cap, and per-owner storage quotas. A personal deployment can use its generated workers.dev address directly. Custom domains and additional WAF rules are optional controls for larger shared deployments, not setup requirements.

#Basic maintenance

  • Keep the Cloudflare account accessible and enable usage notifications if you want alerts.
  • Cloudflare runs log compaction automatically every six hours.
  • If the relay is unavailable, the app keeps working locally and resumes sync when it returns.
  • Removing a relay URL from the app does not delete local app data.

For implementation details and advanced controls, see the relay-cloudflare README.

#Moving existing data to your relay

Your data, identity, and encryption keys derive from your recovery phrase; they are not tied to a particular relay.

  1. Configure the new relay on the device that has the complete local history.
  2. Sync so that history is pushed to the new relay.
  3. Restore the same recovery key on another device, configure the new URL, and confirm the historical and new rows both appear.
  4. Retain the old relay data/configuration until this test succeeds.

#Security model

The relay stores only:

  • encrypted event ciphertext,
  • a pseudonymous owner id,
  • a hash of the owner's write capability, and
  • encrypted attachment chunks.

A malicious or compromised relay can refuse to sync or delete stored events, but it cannot read or forge your app data. Keep an encrypted backup for disaster recovery. See Sync & the relay and the security model for the protocol details.