* Plugins: Convert custom discovery to pull based plugin
This change primarily moves registering custom Discovery implementations
to the pull based DiscoveryPlugin interface. It also keeps the cloud
based discovery plugins re-registering ZenDiscovery under their own name
in order to maintain backwards compatibility. However,
discovery.zen.hosts_provider is changed here to no longer fallback to
discovery.type. Instead, each plugin which previously relied on the
value of discovery.type now sets the hosts_provider to itself if
discovery.type is set to itself, along with a deprecation warning.
At one point in the past when moving out the rest tests from core to
their own subproject, we had multiple test classes which evenly split up
the tests to run. However, we simplified this and went back to a single
test runner to have better reproduceability in tests. This change
removes the remnants of that multiplexing support.
This change moves providing UnicastHostsProvider for zen discovery to be
pull based, adding a getter in DiscoveryPlugin. A new setting is added,
discovery.zen.hosts_provider, to separate the discovery type from the
hosts provider for zen when it is selected. Unfortunately existing
plugins added ZenDiscovery with their own name in order to just provide
a hosts provider, so there are already many users setting the hosts
provider through discovery.type. This change also includes backcompat,
falling back to discovery.type when discovery.zen.hosts_provider is not
set.
* Move all zen discovery classes into o.e.discovery.zen
This collapses sub packages of zen into zen. These all had just a couple
classes each, and there is really no reason to have the subpackages.
* fix checkstyle
UpdateHelper, MetaDataIndexUpgradeService, and some recovery
stuff.
Move ClusterSettings to nullable ctor parameter of TransportService
so it isn't forgotten.
Adds an integration test for the file-based discovery plugin
to test the plugin operates correctly and uses the hosts
configured in `unicast_hosts.txt` with a real cluster
Closes#20459
TransportService is such a central part of the core server, replacing
it's implementation is risky and can cause serious issues. This change removes the ability to
plug in TransportService but allows registering a TransportInterceptor that enables
plugins to intercept requests on both the sender and the receiver ends. This is a commonly used
and overwritten functionality but encapsulates the custom code in a contained manner.
This commit introduces a new plugin for file-based unicast hosts
discovery. This allows specifying the unicast hosts participating
in discovery through a `unicast_hosts.txt` file located in the
`config/discovery-file` directory. The plugin will use the hosts
specified in this file as the set of hosts to ping during discovery.
The format of the `unicast_hosts.txt` file is to have one host/port
entry per line. The hosts file is read and parsed every time
discovery makes ping requests, thus a new version of the file that
is published to the config directory will automatically be picked
up.
Closes#20323
Ryan Ernst
Nik Everett
Simon Willnauer
Ali Beyad