The changes in #32006 mean that the discovery process can no longer use
master-ineligible nodes as a stepping-stone between master-eligible nodes.
This was normally an indication of a strange and possibly-fragile configuration
and was not recommended, but this commit adds a note to the breaking changes
docs to note that this kind of configuration is more obviously broken in recent
versions.
Today the upgrade assistant identifies that discovery configuration is required
in production mode, but links to docs saying to add one of these settings:
- `discovery.seed_hosts`
- `discovery.seed_providers`
- `cluster.initial_master_nodes`
However these settings do not exist in 6.7 so this is unhelpful advice. This
commit adjusts the docs to give more useful advice to users arriving at this
page from the upgrade assistant.
Relates https://discuss.elastic.co/t/174102
The new cluster coordination subsystem introduced in 7.0 will only keep an
unresponsive node in the cluster for 30 seconds, whereas in earlier versions it
might have remained in the cluster for 90 seconds. This commit adds a note to
the migration documentation to that effect.
Renames the following settings to remove the mention of `zen` in their names:
- `discovery.zen.hosts_provider` -> `discovery.seed_providers`
- `discovery.zen.ping.unicast.concurrent_connects` -> `discovery.seed_resolver.max_concurrent_resolvers`
- `discovery.zen.ping.unicast.hosts.resolve_timeout` -> `discovery.seed_resolver.timeout`
- `discovery.zen.ping.unicast.hosts` -> `discovery.seed_addresses`
Today we pass `discovery.zen.minimum_master_nodes` to nodes started up in
tests, but for 7.x nodes this setting is not required as it has no effect.
This commit removes this setting so that nodes are started with more realistic
configurations, and deprecates it.
This commit overhauls the documentation of discovery and cluster coordination,
removing mention of the Zen Discovery module and replacing it with docs for the
new cluster coordination mechanism introduced in 7.0.
Relates #32006
David Turner
James Rodewig
Lisa Cawley