How to make cluster config persistent?

[felipeasf]

Hello, how can I make the cluster config persistent? For example, if I have 3 servers instances online that are already part a cluster and all of them get offline at the same time. There is a way to make them reconnect to the same cluster? The first one to reconnect become master, and the others followers?
To achieve that, the only thing I need to do is implement the in_memory state_mgr.hxx file to save to the disk instead of use memory?

[greensky00]

Hi @felipeasf
Yes, as we commented here

NuRaft/examples/in_memory_state_mgr.hxx

Line 51 in 89d7bd3

// Need to write to disk here, if want to make it durable.

you need to implement save_config and load_config, as well as save_state and read_state. Once those APIs are working, Raft server will automatically call them and reconstruct the last cluster info.

[felipeasf]

Thanks for the answer @greensky00 !
I didn't know about that part of the calls being automatic. I got it working =)
Another question is: There is a way to know when a slave becomes a master?

[greensky00]

You can register a callback function for hooking up a few events:

NuRaft/include/libnuraft/context.hxx

Line 58 in 972f02d

void set_cb_func(cb_func::func_type func) {

The event for becoming a leader is defined here:

NuRaft/include/libnuraft/callback.hxx

Line 53 in 972f02d

BecomeLeader = 6,

[felipeasf]

To register this callback I need the current context, right? As the context is created when the launcher.init function is called, how can I get the current context in order to set the callback?

[greensky00]

context is given at the initialization of Raft server and then becomes read-only. You need to set your callback function at the init time.

And now I realized that if someone uses raft_launcher, there is no way to set the callback function. A simple workaround for now is writing your own init function.

Seems to me the API that setting the callback function should be exposed outside. Will fix that soon. Thanks.

[felipeasf]

I wrote my own init function and is all good now!
Thanks for your kindly support!