Multimaster sync with a nextcloud on the road


I am planning for a Nextcloud installation setup where also a camper is involved. So this is what I am thinking about:

At home I have one nextcloud single server on a PI 3B, doing all stuff for up to 4 users (the family). Accessable from wifi and Internet.

I have a camper where I install a second single server nextcloud also based on a PI 3B (due to power requirements). Because the PI 3B has Wifi, I can create a on-board wifi AP for the onboard smartphones. Those smartphones will be able to access the onboard mextcloud server. One of the main usecases will be for music. This music will then be streamed from the mobile to the onboard stereo systeem over Buetooth. This is the first point where a nicer solution might be possible by hooking up the PI3B straight to the onboard stereo, however, I need to be able to control the music (browse, play, volume, etc) from any smartphone…

I also have a mirrorless camera with wifi. When I go on a (hiking) trip away from the camper and I come back, I need to be able to offload the pictures to the onboard nextcloud.

Now I get back home, I want the onboard nextcloud to sync up with the home nextcloud. Ideally this would be start automagically (based on wifi ESSID found by the on-board nextcloud, for example).

I want this to be a full multimaster sync, because this way they can work as each others backup. From a URL standpoint (access to the data from clients) I can use a DNS trick. When connected to the on-board wifi and thus on-board nextcloud, the smartphones will get IP stack from this server and that way it can trick the on-board clients into thinking they are connecting to the home nextcloud. So, from the clients POV, the connect to 1 (logical) nextcloud server.

For multimaster sync I am planning to use rsync and mysql sync. The problem here is the multimaster part. The on-board server could run out of range (wifi) or out of juice (accu) in the middle of a sync action, potentially leaving me potentially with two corrupted nextcloud instances.

What also might be possible to do is to sync up with the home nextcloud server when on the road and have access to wifi from a campsite, for example (although most campsite wifi AP are horrible). However, syncing photos to the home server while on the road would be a great plus.

What I also not have fully figured out, is power management for the on-board nextcloud server. If the camper is not being used, it should be down. Now, there are a couple of onboard accu’s in the living area which are charged by driving, external power, or solar panels that are on the campers roof, but I doublt that can keep the onboard nextcloud running 24/7 while not using the camper. However, if the onboard nextcloud server is down I loose my ability to backup, unless I can remotely power it on and off. No idea how to do that (yet).

Also good to know is: the camper is always parked close to the home when not in use (wifi connection to the home ESSID should be possible…)

Any comments, tips and directions on this setup, especially the multimaster sync stuff, are highly appreciated!


I was wondering about something similar. Is it possible when sharing a folder that it would be copied and kept in sync, instead of just having access to it trough federation. For backup, and in case of poor connections to either servers, availability reasons.

Need to have some way it not destroying the data if one of them breaks.