One way federation

[ArchangeGabriel]

Hi there, and thanks for the great work on Matrix.

We are wondering for a specific setup if it would be possible to do only one-way federation: our local users would not be able to join rooms on other homeserver, but people from other HS should still be able to join federated rooms in our HS.

[ArchangeGabriel]

I was linked to #5783.

complexity: 0.0 could likely achieve this, am I right?

[erikjohnston]

The room complexity stuff may work, I'm not 100% sure, but its not really want its designed for.

I think the correct way of doing this is using the third_party_event_rules plugin, which allows running arbitrary rules on new events generated by the server. In this case I think you could write a module that denies all joins by local users where there are no other users in the room. I'm not 100% sure that will work well, but if it doesn't then we should expand third party event rules to support this use case.

[erikjohnston]

I'm closing this for now. If it turns out that using third_party_event_rules doesn't work out then we can open more specific issues 👍