Today closing a `ClusterNode` in an `AbstractCoordinatorTestCase` uses
`onNode()` so has no effect if the node is not in the current list of nodes.
It also discards the `Runnable` it creates without having run it, so has no
effect anyway.
This commit makes these tests much stricter about properly closing the nodes
started during `Coordinator` tests, by tracking the persisted states that are
opened, and adds an assertion to catch the trappy requirement that the closing
node still belongs to the cluster.
This commit ensures that cluster state publications to self also go through the transport layer. This
allows voting-only nodes to intercept the publication to self.
Fixes an issue discovered by a test failure where a voting-only node, which was the only
bootstrapped node, would not step down as master after state transfer because publishing to self
would succeed.
Closes#43631
Adds support for the situation where only voting-only nodes are bootstrapped. In that case, they will
still try to become elected and bring full master nodes into the cluster.
A voting-only master-eligible node is a node that can participate in master elections but will not act
as a master in the cluster. In particular, a voting-only node can help elect another master-eligible
node as master, and can serve as a tiebreaker in elections. High availability (HA) clusters require at
least three master-eligible nodes, so that if one of the three nodes is down, then the remaining two
can still elect a master amongst them-selves. This only requires one of the two remaining nodes to
have the capability to act as master, but both need to have voting powers. This means that one of
the three master-eligible nodes can be made as voting-only. If this voting-only node is a dedicated
master, a less powerful machine or a smaller heap-size can be chosen for this node. Alternatively, a
voting-only non-dedicated master node can play the role of the third master-eligible node, which
allows running an HA cluster with only two dedicated master nodes.
Closes#14340
Co-authored-by: David Turner <david.turner@elastic.co>
David Turner
Yannick Welsch