What it is
Local-first apps keep your data on your own device and work whether or not you have a
connection. A relay is what lets a second device catch up: it holds the encrypted changes
until your other devices come online. This app runs that relay on your Umbrel, so the copy
in the middle sits on hardware you own.
It is the relay from the Evolu project, taken straight from the package they
publish and not reimplemented here. Any app built on Evolu can use it.
What the relay can see
Your data is encrypted on your device before it leaves. The relay holds encrypted blobs,
padded so their size says nothing, and never has the key. What it can see is an owner id,
which identifies data without identifying you, along with timestamps and the addresses that
connect.
Self-hosting does not make the data more secret than it already is. What it changes is who
keeps the encrypted copy, who can see that you are syncing at all, and whether anyone can
pull the service out from under you.
Pointing an app at it
Set the address at the bottom of this page as the sync address in your app. Some apps only
offer the field in their developer or advanced settings. Which scheme that field wants
depends on the app: ws:// as shown below, or http://,
which some apps expect because the websocket starts as an HTTP request and they work the
rest out themselves. Same host and same port either way, so try the other one if the first
is refused.
Away from home you will need a way in, such as Tailscale or a reverse proxy with your own
domain. Behind a proxy with a certificate the address becomes wss:// (or
https) on your own domain, without a port number: the proxy listens on 443 and forwards to
this one.
Who may use it
What this app adds is the part a self-hosted relay needs and a public one does not: control
over who may use it. Nobody gets in by default. An owner that connects for the first time is
turned away and lands on the waiting list with its owner id, and you decide
there whether it may stay. One app can use more than one owner id, so expect more than one
row per device.
An owner on the waiting list syncs nothing at all, and nothing of it is stored: the relay
turns the connection away before it starts. Its device keeps everything locally and retries,
so allowing it later still brings the whole history across, and you do not have to be quick.
Owner ids are long and meaningless on purpose. Hover a row and use Label to
give one a name of your own; the name is kept on the Umbrel and is only ever shown here.
