Gordon Brown da20dfd81c
Add cluster-wide shard limit warnings (#34021)
In a future major version, we will be introducing a soft limit on the
number of shards in a cluster based on the number of nodes in the
cluster. This limit will be configurable, and checked on operations
which create or open shards and issue a warning if the operation would
take the cluster over the limit.

There is an option to enable strict enforcement of the limit, which
turns the warnings into errors.  In a future release, the option will be
removed and strict enforcement will be the default (and only) behavior.
2018-10-23 16:35:10 -06:00

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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>>.