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7d52d58747
This commit adds two main pieces, the first is a ClusterInfoService that provides a service running on the master nodes that fetches the total/free bytes for each data node in the cluster as well as the sizes of all shards in the cluster. This information is gathered by default every 30 seconds, and can be changed dynamically by setting the `cluster.info.update.interval` setting. This ClusterInfoService can hopefully be used in the future to weight nodes for allocation based on their disk usage, if desired. The second main piece is the DiskThresholdDecider, which can disallow a shard from being allocated to a node, or from remaining on the node depending on configuration parameters. There are three main configuration parameters for the DiskThresholdDecider: `cluster.routing.allocation.disk.threshold_enabled` controls whether the decider is enabled. It defaults to false (disabled). Note that the decider is also disabled for clusters with only a single data node. `cluster.routing.allocation.disk.watermark.low` controls the low watermark for disk usage. It defaults to 0.70, meaning ES will not allocate new shards to nodes once they have more than 70% disk used. It can also be set to an absolute byte value (like 500mb) to prevent ES from allocating shards if less than the configured amount of space is available. `cluster.routing.allocation.disk.watermark.high` controls the high watermark. It defaults to 0.85, meaning ES will attempt to relocate shards to another node if the node disk usage rises above 85%. It can also be set to an absolute byte value (similar to the low watermark) to relocate shards once less than the configured amount of space is available on the node. Closes #3480