new bootstrap strategy - "supervised"

[sergepetrenko]

Related dev. issue(s): tarantool/tarantool#8509

Product: Tarantool
Since: 3.0.0-alpha3
Root document: https://www.tarantool.io/en/doc/latest/reference/configuration/#cfg-replication-bootstrap-strategy
SME: @ sergepetrenko

Details

The bootstrap_strategy configuration option may now be set to
"supervised".

This strategy works as follows:
When bootstrapping a new replicaset, the nodes do not choose a bootstrap
leader automatically and instead wait for it to be appointed by the
user. The configuration will fail if no bootstrap leader is appointed
during a replication_connect_timeout.

In order to appoint a bootstrap leader, the user has to issue
box.ctl.make_bootstrap_leader() call on the desired node. This must be
done during the initial box.cfg() call.

Possible ways to achieve this are:

1. In interactive mode:

fiber.create(box.cfg, desired_config)
box.ctl.make_bootstrap_leader()

2. Via an init script:

-- Init script:
console.listen(admin_port)
box.cfg(desired_config)
-- User console:
tarantoolctl enter admin port
> box.ctl.make_bootstrap_leader()

When joining a new replica with bootstrap_strategy = "supervised" to
an existing replica set, the replica will not choose the bootstrap
leader automatically, but will instead join to the node on which
box.ctl.make_bootstrap_leader() was issued last. In case such a node
isn't found after a replication_connect_timeout, the configuration
fails.

Requested by @sergepetrenko in tarantool/tarantool@c419cab