elasticsearch trying to allocate a primary shard which is disabled

es_pri_allocate_unassigned.md

Allow routing allocations:

curl -XPUT localhost:9200/_cluster/settings -d '{
                "transient" : {
                    "cluster.routing.allocation.enable" : "all"
                }
        }'

Reallocate unassigned shards, allowing primary allocations:

curl -s localhost:9200/_cat/shards | grep UNASS | while read line ; do \
  read -a fields <<<"$line" ;
  curl -XPOST -d '{ 
    "commands" : [ 
      { 
        "allocate" : {
          "index" : "'${fields[0]}'",
          "shard" : '${fields[1]}',
          "node" : "elasticsearch-'$(hostname)'",
          "allow_primary": "true"
        }
      }
    ]
  }' http://localhost:9200/_cluster/reroute?pretty ; done

Just a heads up, I used this on a 21 node cluster (Elasticsearch 1.7) where one node had fallen over and after restarting the node there was an individual shard in 2 separate indexes that wouldn't allocate. I used this script to force the cluster to allocate the shards in an attempt to get the cluster out of RED, and unsurprisingly it "reset" the shard entirely and I lost 20 million docs or so.

There is no allocation explain API on 1.7 so I still don't know what I'll do if this occurs in the future.