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[[breaking_70_cluster_changes]]
=== Cluster changes

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==== `:` 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 `:`.

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==== 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.

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==== 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.

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==== Cluster-wide shard soft limit
Clusters now have soft limits on the total number of open shards in the cluster
based on the number of nodes and the `cluster.max_shards_per_node` cluster
setting, to prevent accidental operations that would destabilize the cluster.
More information can be found in the <<misc-cluster,documentation for that setting>>.

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==== Discovery configuration is required in production
Production deployments of Elasticsearch now require at least one of the following settings
to be specified in the `elasticsearch.yml` configuration file:

- `discovery.zen.ping.unicast.hosts`
- `discovery.zen.hosts_provider`
- `cluster.initial_master_nodes`