The AdminAPI includes support for InnoDB ReplicaSet, that
enables you to administer a set of MySQL instances running
asynchronous GTID-based replication in a similar way to
InnoDB cluster. An InnoDB ReplicaSet consists of a single
primary and multiple secondaries (traditionally referred to as
the MySQL replication master and slaves). You administer your
replica sets using a
ReplicaSet object and
the AdminAPI operations, for example to check the status of
the InnoDB ReplicaSet, and manually failover to a new primary
in the event of a failure. Similar to InnoDB cluster, MySQL Router
supports bootstrapping against InnoDB ReplicaSet, which means
you can automatically configure MySQL Router to use your
InnoDB ReplicaSet without having to manually configure files.
This makes InnoDB ReplicaSet a quick and easy way to get MySQL
replication and MySQL Router up and running, making it well suited
to scaling out reads, and provides manual failover capabilities
in use cases that do not require the high availability offered
by InnoDB cluster.
In addition to deploying an InnoDB ReplicaSet using AdminAPI, you can adopt an existing replication setup. AdminAPI configures the InnoDB ReplicaSet based on the topology of the replication setup. Once the replication setup has been adopted, you administer it in the same way as an InnoDB ReplicaSet deployed from scratch. This enables you to take advantage of AdminAPI and MySQL Router without the need to create a new replica set. For more information see Section 21.6.4, “Adopting an Existing Replication Set Up”.
An InnoDB ReplicaSet has several limitations compared to a InnoDB cluster and thus, it is recommended that you deploy InnoDB cluster wherever possible. Generally, a InnoDB ReplicaSet on its own does not provide high availability. Among the limitations of InnoDB ReplicaSet are:
No automatic failover. In events where the primary becomes unavailable, a failover needs to be triggered manually using AdminAPI before any changes are possible again. However, secondary instances remain available for reads.
No protection from partial data loss due to an unexpected halt or unavailability. Transactions that have not yet been applied by the time of the halt could become lost.
No protection against inconsistencies after a crash or unavailability. If a failover promotes a secondary while the former primary is still available (for example due to a network partition), inconsistencies could be introduced because of the split-brain.