List members of cluster

[plunkettscott]

This is more of a general question because I can't seem to find an obvious answer.

Is it possible to list the members of an olric cluster from an Olric embedded member instance? I'm trying to use olric not only for caching but also as a cluster implementation while running an embedded member in each instance of the app. I can't seem to find a way to get the members of the cluster (or even access the memberlist implementation's list of nodes.)

I expected Stats() to offer this information but it seems to not offer a list of members, but instead returns important members in the cluster, such as the coordinator or owners and previous owners of particular partitions.

If it's not possible to do this currently would it be feasible to export this information for use when running as an embedded member? I'm not needing to subscribe to member join/leave, only list the members at any given time. For reference, my use case is to return the list of members via the application's API so that a glance at the web app can show the names of all members.

[buraksezer]

Hi @plunkettscott

I'm sorry for my delayed response. The feature you requested is quite easy to implement. internal/discovery package already provides a list of known alive members. See this: https://github.com/buraksezer/olric/blob/master/internal/discovery/discovery.go#L286

We can easily expose this info in stats: https://github.com/buraksezer/olric/blob/master/stats.go#L32

You should know that internal/discovery provides low-level functionalities. So a member in the members slice may not be an effective cluster member. If you need a list of properly bootstrapped members, we may extract this data from the routing table.

[plunkettscott]

Thanks, @buraksezer!

I definitely think listing bootstrapped cluster members is the answer, not necessarily listing members that may not be bootstrapped. Ideally, if it's easier to list all members of a cluster (even those not yet bootstrapped), I think it would be beneficial to also include the ability to see the state of those members (bootstrapped, not bootstrapped, unresponsive, etc.)

[buraksezer]

Hi @plunkettscott

I have just implemented the feature and released v0.3.4.

Stats now exposes bootstrapped members of the cluster.

type Stats struct {
	Cmdline            []string
	ReleaseVersion     string
	Runtime            Runtime
	ClusterCoordinator discovery.Member
	Partitions         map[uint64]Partition
	Backups            map[uint64]Partition
	ClusterMembers     map[uint64]discovery.Member
}

Please don't hesitate to open issues for further issues or feature requests.