Can we use weighted leader election? (And java 7 question)

[Joe Fair]

I have 8 servers in two datacenters.  I'd prefer servers 1-4 to be a leader if available, and 5-8 to be a leader if 1-4 is down.

I currently have a system that uses weighted values (100, 200, etc.) and the highest one is the leader.

Can that be done in jgroups-raft?  Where would you suggest I start?

Also, is there already a port of java 7?

Thx,

Joe

[Bela Ban]

Hi Joe,

On 02/06/17 16:18, Joe Fair wrote:
> I have 8 servers in two datacenters. I'd prefer servers 1-4 to be a
> leader if available, and 5-8 to be a leader if 1-4 is down.
> I currently have a system that uses weighted values (100, 200, etc.) and
> the highest one is the leader.
>
> Can that be done in jgroups-raft? Where would you suggest I start?

This is possible in JGroups itself [1], but not in jgroups-raft. The
reason is that jgroups-raft implements the Raft election specification
pretty closely [2], and Raft knows no weighted election.

There are 2 criteria for leader election: (1) majority of votes and (2)
highest log index. (1) could be weighted, but not (2). For example, if
you have a leader election and server 6 has the highest log index (e.g.
after a network partition healed), then none of servers 1-4 should
become leader, but server 6 should become leader.

So, in a nutshell, I believe adding weighted election would break the
semantics of Raft.

> Also, is there already a port of java 7?

What do you mean? jgroups-raft works on Java 8, but still uses JGroups
3.6.x. Do you mean upgrading jgroups-raft to use JGroups 4.0?

Cheers

[1] http://www.jgroups.org/manual4/index.html#MembershipChangePolicy
[2]
https://github.com/belaban/jgroups-raft/blob/master/src/org/jgroups/protocols/raft/ELECTION.java

> Thx,
> Joe
>
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Bela Ban | http://www.jgroups.org