Cluster: Is it necessary to have multiple servers?

Question

Clusters

It's a bit unclear what actually is a cluster?

If on one physical server, I raised the following configuration via docker swarm or k8s:
nginx - 2 copies of
php-fpm - 5 copies of
mysql - 1 copy

1. is this configuration a cluster, or is it necessary that the copies be spread over several servers?

2. and whether I understand correctly that such a configuration does not provide fault tolerance, but only gives additional. throughput (if iron allows)?

Answer 1

1.
2. yes, but not the bandwidth of the
cluster - 2 or more copies of applications on different iron servers

Answer 2

2. extra bandwidth? - well, if only BEFORE the database, and then there is only one database, respectively, the performance of the entire application will not change anyway.