Today we support a static list of seed hosts in core Elasticsearch, and allow a
dynamic list of seed hosts to be provided via a file using the `discovery-file`
plugin. In fact the ability to provide a dynamic list of seed hosts is
increasingly useful, so this change moves this functionality to core
Elasticsearch to avoid the need for a plugin.
Furthermore, in order to start up nodes in integration tests we currently
assign a known port to each node before startup, which unfortunately sometimes
fails if another process grabs the selected port in the meantime. By moving the
`discovery-file` functionality into the core product we can use it to avoid
this race.
This change also moves the expected path to the file from
`$ES_PATH_CONF/discovery-file/unicast_hosts.txt` to
`$ES_PATH_CONF/unicast_hosts.txt`. An example of this file is not included in
distributions.
For BWC purposes the plugin still exists, but does nothing more than create the
example file in the old location, and issue a warning when it is used. We also
continue to support the old location for the file, but warn about its
deprecation.
Relates #29244Closes#33030
Plugins: Remove pluggability of ZenPing
ZenPing is the part of zen discovery which knows how to ping nodes.
There is only one alternative implementation, which is just for testing.
This change removes the ability to add custom zen pings, and instead
hooks in the MockZenPing for tests through an overridden method in
MockNode. This also folds in the ZenPingService (which was really just a
single method) into ZenDiscovery, and removes the idea of having
multiple ZenPing instances. Finally, this was the last usage of the
ExtensionPoint classes, so that is also removed here.
David Turner
Clinton Gormley
Ryan Ernst
Ali Beyad