Trait foca::Identity

source · [−]
pub trait Identity: Clone + Eq + Debug {
    fn renew(&self) -> Option<Self>;
    fn has_same_prefix(&self, other: &Self) -> bool;
}
Expand description

Identity is a cluster-global identifier. It qualifies a cluster member and there must not be multiple members sharing the same identity.

When talking about network protocols we’re often talking about an IP-address paired with a port number (std::net::SocketAddr, for example), but Foca doesn’t actually care about what’s inside an identity so long as its unique.

This allows implementations to make their identities as lean or large as they need. For example: if every Foca instance will bind to the same port, there’s no need to make the port number part of the identity.

That said, most of the time it’s useful to have more information in a identity than just a way to figure out a “network” address. And that’s because of how SWIM works: when an identity is declared down or deliberately leaves the cluster, it cannot rejoin for a relatively long while, so a little extra metadata allows us to come back as fast as possible.

See examples/identity_golf.rs for ideas

Required Methods

Opt-in on auto-rejoining by providing a new identity.

When Foca detects it’s been declared Down by another member of the cluster, it will call Self::renew() on its current identity and if it yields a new one will immediately switch to it and notify the cluster so that downtime is minimized.

Optionally accept Announce messages addressed to an identity that isn’t exactly the same as ours.

Foca discards messages that aren’t addressed to its exact identity. This means that if your identity has an unpredictable field (a UUID or a random number, for example), nobody will be able to join with us directly.

The Self::has_same_prefix method is how we teach Foca to relax this restriction: Upon receiving an Announce message it will call current_id.has_same_prefix(dst) and if it yields true the message will be accepted and the new member will be allowed to join the cluster.

Implementations on Foreign Types

Implementors