Sometimes, servers fail to serve for so many possible reasons. If a read replica fails, so be it; replace it or add another one, it will get the data as it joins the cluster. If a core server fails, the cluster handles it too. The graph is recreated via the other cores. You can see it yourself:
- Stop a core server.
- Go through its folders, and remove data/databases and data/cluster-state.
- Restart it (the more data, the more time it will take).
- Watch the log file to see when it is ready.
- Go to its Neo4j browser.
- Be amazed.
This is so simple, it reminds me what a speaker said at a graph connect conference: "We do the hard things so you don't have to."
If all your core servers fail, first find the reason, for it is very unlikely ...