I’m sure this has been answered before somehow, but I couldn’t find my exact situation.
I have five devices sharing some folders. I’ve set them all up over the last few years, mostly set-and-forget. Win, Linux, Mac, Android. So I’m a long-time user but not in any way an expert.
Now today I added a new folder f1 on device A. I shared that with B and with C. I accepted on B, and accepted on C. All good. But how do I now make sure B and C are connected so they still sync if A is offline? I think if I tore it all down and made some device(s) “introducers” then it might happen automatically, but given I’ve already shared it, what’s the simplest way? And then to add devices D and E, should I set up “introducers” to make sure I have all devices fully connected, sharing my folder f1?
As stated at https://docs.syncthing.net/users/introducer.html, it’s best if only one device is set as “Introducer”. It’s most useful when set on a device that’s connected with all other devices.
Now that you’ve already shared Syncthing folder f1 from node A with nodes B and C, to complete the mesh, all that’s needed is to edit the Syncthing folder settings on B and C to extend the sharing.
If C isn’t already a known remote device on B, add it just as you did on A (i.e. A includes B and C as remote devices). While adding C as a remote device on B, you can also choose to share Syncthing folder f1 with C (or add it later via [Edit] → [Sharing] in the folder panel).
As long as the Syncthing folder ID is the same, C will recognize that it’s the same folder as the one it’s already sharing with A, treating it as equal to the one hosted by B. Whenever A is unavailable, B and C will not only continue syncing folder f1 with each other, A will download changes from both B and C once it’s connected again.
Repeat the process on C to end up with the following connections where every node is connected to all other nodes:
A <-> B
A <-> C
B <-> C
(Of course, the f1 folder must be set to “Send & Receive” on all participating nodes, otherwise there won’t be the full redundancy you’re looking for.)
I think there is an easy answer here, introducers are not required. You simply open the Web GUI on devices B and C, edit the respective folder and under the “Sharing” tab, check the boxes for the other devices respectively. Needs to be done on both sides of each link, but if one has already done it, a notification appears on the other side to accept with just one button press.