Task management API

It is also possible to retrieve information for a particular task. The following example retrieves information about task oTUltX4IQMOUUVeiohTt8A:124:

response = client.tasks.get(
  task_id: 'oTUltX4IQMOUUVeiohTt8A:124'
)
puts response

GET _tasks/oTUltX4IQMOUUVeiohTt8A:124

If the task isn’t found, the API returns a 404.

To retrieve all children of a particular task:

response = client.tasks.list(
  parent_task_id: 'oTUltX4IQMOUUVeiohTt8A:123'
)
puts response

GET _tasks?parent_task_id=oTUltX4IQMOUUVeiohTt8A:123

If the parent isn’t found, the API does not return a 404.

You can also use the detailed request parameter to get more information about the running tasks. This is useful to distinguish tasks from each other but is more costly to execute. For example, fetching all searches using the detailed request parameter:

response = client.tasks.list(
  actions: '*search',
  detailed: true
)
puts response

GET _tasks?actions=*search&detailed

The API returns the following result:

{
  "nodes" : {
    "oTUltX4IQMOUUVeiohTt8A" : {
      "name" : "H5dfFeA",
      "transport_address" : "127.0.0.1:9300",
      "host" : "127.0.0.1",
      "ip" : "127.0.0.1:9300",
      "tasks" : {
        "oTUltX4IQMOUUVeiohTt8A:464" : {
          "node" : "oTUltX4IQMOUUVeiohTt8A",
          "id" : 464,
          "type" : "transport",
          "action" : "indices:data/read/search",
          "description" : "indices[test], types[test], search_type[QUERY_THEN_FETCH], source[{\"query\":...}]",
          "start_time_in_millis" : 1483478610008,
          "running_time_in_nanos" : 13991383,
          "cancellable" : true,
          "cancelled" : false
        }
      }
    }
  }
}

The new description field contains human readable text that identifies the particular request that the task is performing such as identifying the search request being performed by a search task like the example above. Other kinds of tasks have different descriptions, like _reindex which has the source and the destination, or _bulk which just has the number of requests and the destination indices. Many requests will only have an empty description because more detailed information about the request is not easily available or particularly helpful in identifying the request.

The task API can also be used to wait for completion of a particular task. The following call will block for 10 seconds or until the task with id oTUltX4IQMOUUVeiohTt8A:12345 is completed.

response = client.tasks.get(
  task_id: 'oTUltX4IQMOUUVeiohTt8A:12345',
  wait_for_completion: true,
  timeout: '10s'
)
puts response

GET _tasks/oTUltX4IQMOUUVeiohTt8A:12345?wait_for_completion=true&timeout=10s

You can also wait for all tasks for certain action types to finish. This command will wait for all reindex tasks to finish:

response = client.tasks.list(
  actions: '*reindex',
  wait_for_completion: true,
  timeout: '10s'
)
puts response

GET _tasks?actions=*reindex&wait_for_completion=true&timeout=10s

If a long-running task supports cancellation, it can be cancelled with the cancel tasks API. The following example cancels task oTUltX4IQMOUUVeiohTt8A:12345:

response = client.tasks.cancel(
  task_id: 'oTUltX4IQMOUUVeiohTt8A:12345'
)
puts response

POST _tasks/oTUltX4IQMOUUVeiohTt8A:12345/_cancel

The task cancellation command supports the same task selection parameters as the list tasks command, so multiple tasks can be cancelled at the same time. For example, the following command will cancel all reindex tasks running on the nodes nodeId1 and nodeId2.

response = client.tasks.cancel(
  nodes: 'nodeId1,nodeId2',
  actions: '*reindex'
)
puts response

POST _tasks/_cancel?nodes=nodeId1,nodeId2&actions=*reindex

A task may continue to run for some time after it has been cancelled because it may not be able to safely stop its current activity straight away, or because Elasticsearch must complete its work on other tasks before it can process the cancellation. The list tasks API will continue to list these cancelled tasks until they complete. The cancelled flag in the response to the list tasks API indicates that the cancellation command has been processed and the task will stop as soon as possible. To troubleshoot why a cancelled task does not complete promptly, use the list tasks API with the ?detailed parameter to identify the other tasks the system is running and also use the Nodes hot threads API to obtain detailed information about the work the system is doing instead of completing the cancelled task.

The task lists returned by task API commands can be grouped either by nodes (default) or by parent tasks using the group_by parameter. The following command will change the grouping to parent tasks:

response = client.tasks.list(
  group_by: 'parents'
)
puts response

GET _tasks?group_by=parents

The grouping can be disabled by specifying none as a group_by parameter:

response = client.tasks.list(
  group_by: 'none'
)
puts response

GET _tasks?group_by=none

The X-Opaque-Id header, when provided on the HTTP request header, is going to be returned as a header in the response as well as in the headers field for in the task information. This allows to track certain calls, or associate certain tasks with the client that started them:

curl -i -H "X-Opaque-Id: 123456" "http://localhost:9200/_tasks?group_by=parents"

The API returns the following result:

HTTP/1.1 200 OK
X-Opaque-Id: 123456 
content-type: application/json; charset=UTF-8
content-length: 831

{
  "tasks" : {
    "u5lcZHqcQhu-rUoFaqDphA:45" : {
      "node" : "u5lcZHqcQhu-rUoFaqDphA",
      "id" : 45,
      "type" : "transport",
      "action" : "cluster:monitor/tasks/lists",
      "start_time_in_millis" : 1513823752749,
      "running_time_in_nanos" : 293139,
      "cancellable" : false,
      "headers" : {
        "X-Opaque-Id" : "123456" 
      },
      "children" : [
        {
          "node" : "u5lcZHqcQhu-rUoFaqDphA",
          "id" : 46,
          "type" : "direct",
          "action" : "cluster:monitor/tasks/lists[n]",
          "start_time_in_millis" : 1513823752750,
          "running_time_in_nanos" : 92133,
          "cancellable" : false,
          "parent_task_id" : "u5lcZHqcQhu-rUoFaqDphA:45",
          "headers" : {
            "X-Opaque-Id" : "123456" 
          }
        }
      ]
    }
  }
}