was created on Dec 15, 1999

YELLOW status in Elasticsearch

The status is yellow because we have unassigned shards.
In this case we have one node cluster, but our indices all have number_of_replicas: 1 (which is the default). So we have to add a second node to our cluster, or just set "number_of_replicas: 0" globally:
curl -XPUT -H "Content-Type: application/json" 'localhost:9200/_all/_settings' -d '{"index" : {"number_of_replicas" : 0}}'