I have 7 MySQL servers in different locations. All servers has same database with same structure. All tables are structured with UUID based primary keys. (No auto increment values).
1 (Central) server is always connected to the network. (Internet) All other 6 servers can get connected/disconnected from the network anytime.
All 6 servers must have an ability to work individually (Read/Write) and locally when not connected to internet.
They must replicate each other when network connected.
Once all databases completely replicated, all databases must have same contents of data. (Including Main server)
I just mentioned 1 server as a main server here. (But no any main server). It is main server, when all other 6 are not connected, because head office use it to query past reports from it.
I have read about MySQL group replication (Multi Primary Mode). Is it possible to use it in my requirement. Please advise me if someone already have this experience.
Group replication assumes all servers will contain the same data, and when you join a new server it will fetch from the group the data it is missing. However, if the server has more data than the group, it won't be able to join.
So, in theory your setup will only work if these 6 servers don't receive writes and diverge while "offline", because if they do, you can no longer add them back to a group (without extra reconciliation operations).