config: isolated mode for an instance

[Totktonada]

Related dev. issue(s): tarantool/tarantool#10796

Product: Tarantool
Since: 3.3.0
Audience/target: application developers, administrators
Root document:

• https://www.tarantool.io/en/doc/latest/reference/configuration/configuration_reference/
• (possibly somewhere in) https://www.tarantool.io/en/doc/latest/admin/replication/
  SME: @ Totktonada

Details

The option is to temporary isolate an instance to perform replicaset repairing activities: debug a problem on the isolated instance (without affecting the non-isolated part) or extract some data from the isolated instance and apply them on the non-isolated part of the replicaset.

groups:
  g:
    replicasets:
      r:
        instances:
          i-001: {}
          i-002: {}
          i-003: {}
          i-004:
            isolated: true

In this mode the instance doesn't perform processing of iproto requests, doesn't perform background data modifications and refuses to accept updates from other replicaset members. Also, other replicaset members don't replicate data from the isolated instance.

Technically speaking, when the option is enabled, the following actions are performed:

1. iproto stops listening for new connections.
2. iproto drops all the current connections.
3. The instance goes to read-only mode.
4. The instance is disconnected from all the replication upstreams.
5. Other replicaset members exclude the isolated instance from the replication upstreams.

One new startup constraint is added in the isolated mode:

1. The instance can't be bootstrapped (a local snapshot is required to start).

Definition of done

• Describe the new option in the configuration reference
• Verify whether anything else should be updated in the documentation