add API to list voters

[illotum]

Proposed Changes

This is a small addition, high-level API to list voters of a Ra cluster. To be used wherever an active quorum list is needed instead of ra:members.

Types of Changes

• Bug fix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (correction or otherwise)
• Cosmetics (whitespace, appearance)

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

[michaelklishin]

@illotum our team would like to ask for another API extension. This one is fine for where it will be used in RabbitMQ, so I guess we can keep it.

The function we'd like to see is a version of ra:members/1 that would return a map with a more detailed view of cluster members.

ra:members_with_details/1 and ra:members_ext/1 are two named proposed. WDYT?

[kjnilsson]

On second thought I think ra:members_info/1 would be a good name, effectively returning what's in the cluster key of the ra_state() map. The leader doesn't update it's own ra_peer_state() so that needs to be filled in on the fly.

[illotum]

For sure! I usually lean towards minimal changes, but the extended API covers all my needs and more.

[kjnilsson]

For sure! I usually lean towards minimal changes, but the extended API covers all my needs and more.

I think with all the peer info we can probably make better external decision on stuff like member changes without further probing. I have on a couple of occasions wished I could get this information in an easier way. ra:voters/1 is very specific the ra module API is growing quite large and having a more generic function avoids us having to add yet another function in the future.

[illotum]

Following on the rabbitmq-server#10394 thread, lets revert this merge then and I'll go ahead with a proper member_info.

[michaelklishin]

Done.