elasticsearch/docs/reference/migration/migrate_7_0/cluster.asciidoc

[[breaking_70_cluster_changes]]
=== Cluster changes

==== `:` is no longer allowed in cluster name

Due to cross-cluster search using `:` to separate a cluster and index name,
cluster names may no longer contain `:`.

==== New default for `wait_for_active_shards` parameter of the open index command

The default value for the `wait_for_active_shards` parameter of the open index API
is changed from 0 to 1, which means that the command will now by default wait for all
primary shards of the opened index to be allocated.

==== Shard preferences `_primary`, `_primary_first`, `_replica`, and `_replica_first` are removed
These shard preferences are removed in favour of the `_prefer_nodes` and `_only_nodes` preferences.