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Cluster Allocation Explain API

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Cluster Allocation Explain API

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The cluster allocation explanation API is designed to assist in answering the question "why is this shard unassigned?". To explain the allocation (on unassigned state) of a shard, issue a request like:

The cluster allocation explain API is new and should still be considered experimental. The API may change in ways that are not backwards compatible

$ curl -XGET 'http://localhost:9200/_cluster/allocation/explain' -d'{
  "index": "myindex",
  "shard": 0,
  "primary": false
}'

Specify the index and shard id of the shard you would like an explanation for, as well as the primary flag to indicate whether to explain a primary or replica shard.

The response looks like:

{
  "shard" : {
    "index" : "myindex",
    "index_uuid" : "KnW0-zELRs6PK84l0r38ZA",
    "id" : 0,
    "primary" : false
  },
  "assigned" : false,                             
  "shard_state_fetch_pending": false,             
  "unassigned_info" : {
    "reason" : "INDEX_CREATED",                   
    "at" : "2016-03-22T20:04:23.620Z"
  },
  "allocation_delay_ms" : 0,                      
  "remaining_delay_ms" : 0,                       
  "nodes" : {
    "V-Spi0AyRZ6ZvKbaI3691w" : {
      "node_name" : "H5dfFeA",
      "node_attributes" : {                       
        "bar" : "baz"
      },
      "store" : {
        "shard_copy" : "NONE"                     
      },
      "final_decision" : "NO",                    
      "final_explanation" : "the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
      "weight" : 0.06666675,                      
      "decisions" : [ {                           
        "decider" : "filter",
        "decision" : "NO",
        "explanation" : "node does not match index include filters [foo:\"bar\"]"
      } ]
    },
    "Qc6VL8c5RWaw1qXZ0Rg57g" : {
      "node_name" : "bGG90GE",
      "node_attributes" : {
        "bar" : "baz",
        "foo" : "bar"
      },
      "store" : {
        "shard_copy" : "AVAILABLE"
      },
      "final_decision" : "NO",
      "final_explanation" : "the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
      "weight" : -1.3833332,
      "decisions" : [ {
        "decider" : "same_shard",
        "decision" : "NO",
        "explanation" : "the shard cannot be allocated on the same node id [Qc6VL8c5RWaw1qXZ0Rg57g] on which it already exists"
      } ]
    },
    "PzdyMZGXQdGhqTJHF_hGgA" : {
      "node_name" : "DKDM97B",
      "node_attributes" : { },
      "store" : {
        "shard_copy" : "NONE"
      },
      "final_decision" : "NO",
      "final_explanation" : "the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
      "weight" : 2.3166666,
      "decisions" : [ {
        "decider" : "filter",
        "decision" : "NO",
        "explanation" : "node does not match index include filters [foo:\"bar\"]"
      } ]
    }
  }
}

	Whether the shard is assigned or unassigned
	Whether information about the shard is still being fetched
	Reason for the shard originally becoming unassigned
	Configured delay before the shard can be allocated
	Remaining delay before the shard can be allocated
	User-added attributes the node has
	The shard copy information for this node and error (if applicable)
	Final decision and explanation of whether the shard can be allocated to this node
	Weight for how much the allocator would like to allocate the shard to this node
	List of node decisions factoring into final decision about the shard

For a shard that is already assigned, the output looks similar to:

{
  "shard" : {
    "index" : "only-foo",
    "index_uuid" : "KnW0-zELRs6PK84l0r38ZA",
    "id" : 0,
    "primary" : true
  },
  "assigned" : true,
  "assigned_node_id" : "Qc6VL8c5RWaw1qXZ0Rg57g",      
  "shard_state_fetch_pending": false,
  "allocation_delay_ms" : 0,
  "remaining_delay_ms" : 0,
  "nodes" : {
    "V-Spi0AyRZ6ZvKbaI3691w" : {
      "node_name" : "bGG90GE",
      "node_attributes" : {
        "bar" : "baz"
      },
      "store" : {
        "shard_copy" : "NONE"
      },
      "final_decision" : "NO",
      "final_explanation" : "the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
      "weight" : 1.4499999,
      "decisions" : [ {
        "decider" : "filter",
        "decision" : "NO",
        "explanation" : "node does not match index include filters [foo:\"bar\"]"
      } ]
    },
    "Qc6VL8c5RWaw1qXZ0Rg57g" : {
      "node_name" : "I8hydUG",
      "node_attributes" : {
        "bar" : "baz",
        "foo" : "bar"
      },
      "store" : {
        "shard_copy" : "AVAILABLE"
      },
      "final_decision" : "ALREADY_ASSIGNED",        
      "final_explanation" : "the shard is already assigned to this node",
      "weight" : 0.0,
      "decisions" : [ {
        "decider" : "same_shard",
        "decision" : "NO",
        "explanation" : "the shard cannot be allocated on the same node id [Qc6VL8c5RWaw1qXZ0Rg57g] on which it already exists"
      } ]
    },
    "PzdyMZGXQdGhqTJHF_hGgA" : {
      "node_name" : "H5dfFeA",
      "node_attributes" : { },
      "store" : {
        "shard_copy" : "NONE"
      },
      "final_decision" : "NO",
      "final_explanation" : "the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
      "weight" : 3.6999998,
      "decisions" : [ {
        "decider" : "filter",
        "decision" : "NO",
        "explanation" : "node does not match index include filters [foo:\"bar\"]"
      } ]
    }
  }
}

	Node the shard is currently assigned to
	The decision is "ALREADY_ASSIGNED" because the shard is currently assigned to this node

You can also have Elasticsearch explain the allocation of the first unassigned shard it finds by sending an empty body, such as:

$ curl -XGET 'http://localhost:9200/_cluster/allocation/explain'

If you would like to include all decisions that were factored into the final decision, the include_yes_decisions parameter will return all decisions:

$ curl -XGET 'http://localhost:9200/_cluster/allocation/explain?include_yes_decisions=true'

Additionally, you can return information gathered by the cluster info service about disk usage and shard sizes by setting the include_disk_info parameter to true:

$ curl -XGET 'http://localhost:9200/_cluster/allocation/explain?include_disk_info=true'

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