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Elasticsearch

Elasticsearch is a distributed search server based on Apache Lucene, which acts as the application’s search and analytic engine. Some solutions to common problems with Elasticsearch and AtoM are below.

Disable auto-discovery

To prevent Elasticsearch from auto-discovering other nodes on the network, add the following to /etc/elasticsearch/config/elasticsearch.yml

node.local: true # disable network

Check the status of your Elasticsearch index

AtoM includes a command-line task that will allow a system administrator to review the status of AtoM’s Elasticsearch index without having to access any configuration files. The task output will include:

  • Search host
  • Port
  • Index name
  • Document index status for all primary entity types in AtoM (including Accession, Actor, AIP, Function, Information object, Repository, and Term)

The task should be run from AtoM’s root installation directory. It will not make any changes, but can provide useful information when troubleshooting issues or seeking support. To run the task:

php symfony search:status

Sample response:

An image of a typical response to the search:status task

Check cluster health

See: http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/cluster-health.html

curl -XGET 'http://localhost:9200/_cluster/health?pretty=true'

Sample output:

{
  "cluster_name" : "testcluster",
  "status" : "green",
  "timed_out" : false,
  "number_of_nodes" : 2,
  "number_of_data_nodes" : 2,
  "active_primary_shards" : 5,
  "active_shards" : 10,
  "relocating_shards" : 0,
  "initializing_shards" : 0,
  "unassigned_shards" : 0
}

Find problem shards

If the Cluster health returns as “red” or “yellow” you can find problem shards with:

curl -XGET 'http://localhost:9200/_cluster/health/?level=shards&pretty=true'

You can redirect the STDOUT to a text file and search for “red” or “yellow” to find the problem indexes/shards.

Cluster health is yellow

If Cluster health returns as yellow, it “means that the primary shard is allocated but replicas are not” [1]. This often means that you have do not have enough ES nodes in your cluster to support the desired number of replicas of an index. This happens when you have indexes with number_of_replicas > (the number of ES nodes you are running - 1). For instance if you only have 1 ES node, number_of_replicas should be set to 0.

In the default AtoM installation instructions, we only configure one node with no replicas, so the yellow cluster health is not surprising - and if the search index is lost, it can easily be repopulated from the database using the Populate search index task.

However, to reduce (or increase) the number of replicas on an existing index, you can use:

curl -XPUT 'localhost:9200/my_index/_settings' -d '
{
    "index" : {
        "number_of_replicas" : 0
   }
}

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