Connection Limits

New in version 1.13.0.

Connection limits can be set to prevent Syncthing from establishing connections under some circumstances. For the most part you want Syncthing to connect to all its configured peers, thus you should usually not use this option. Connection limits are useful in specific scenarios concerning large deployments only, and care must be taken when selecting limits to work in that scenario. The general recommendation is to leave these settings at their default of zero, meaning unlimited.

Mechanism

There are two limits, called enough and max. In short, once there are enough connections Syncthing will stop trying to connect to other devices; when the max is reached Syncthing will also refuse incoming connections.

Either can be set individually, leaving the other at zero, or both can be set. When setting both values, enough should be smaller than max or it will have no effect (Syncthing will also stop connecting outwards once max is reached).

Scenarios

Load Balancing

Consider a setup with a handful “servers” and many “clients”. The servers are fully connected amongst each other and essentially equivalent. The clients should connect to one server each in order to receive updates. One way of accomplishing this is to divide the clients into (static) groups and configure each group to connect to a specific server.

Another way is using connection limits, configuring each client identically for all servers but setting the max connection limit to 1. This has the advantage that if one server becomes unavailable the clients will migrate to other servers.

When establishing new connections Syncthing will preferentially connect to devices it was recently connected to, thus clients will usually stay on the same server over a restart.