Bulk write to multiple aliases throws 500 error starting in 5.5.3

[BradHarris]

Elasticsearch version (bin/elasticsearch --version): 5.5.3

Plugins installed: x-pack (it comes with the docker version of ES)

JVM version (java -version):
openjdk version "1.8.0_141"
OpenJDK Runtime Environment (build 1.8.0_141-b16)
OpenJDK 64-Bit Server VM (build 25.141-b16, mixed mode)

OS version (uname -a if on a Unix-like system): docker image uses centos:7
Linux cf214e385aa3 4.10.0-33-generic #37-Ubuntu SMP Fri Aug 11 10:55:28 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

Description of the problem including expected versus actual behavior:

Steps to reproduce:

Please include a minimal but complete recreation of the problem, including
(e.g.) index creation, mappings, settings, query etc. The easier you make for
us to reproduce it, the more likely that somebody will take the time to look at it.

1. spin up a 5.5.3 ES instance with docker: docker run -p 9200:9200 -p 9300:9300 -e "discovery.type=single-node" docker.elastic.co/elasticsearch/elasticsearch:5.5.3
2. run this script:

#!/usr/bin/env bash

# creates an index called my-data with 2 write aliases: write-alias-1 and write-alias-2
curl -u "elastic:changeme" -XPUT "http://localhost:9200/my-data" -H 'Content-Type: application/json' -d'
{
  "aliases": {
    "write-index-1": {},
    "write-index-2": {}
  }
}
'

# bulk writes 2 documents using the same _id but with different write aliases
curl -u "elastic:changeme" -XPOST "http://localhost:9200/_bulk?pretty" -H 'Content-Type: application/json' -d'
{"index":{"_index": "write-index-1","_type": "data", "_id": "1"}}
{"hello": "hello1"}
{"index":{"_index": "write-index-2","_type": "data", "_id": "1"}}
{"hello": "hello2"}
'

Provide logs (if relevant):
output from the bulk call:

{
  "took" : 0,
  "errors" : true,
  "items" : [
    {
      "index" : {
        "_index" : "my-data",
        "_type" : "data",
        "_id" : "1",
        "status" : 500,
        "error" : {
          "type" : "illegal_state_exception",
          "reason" : "Action indices:data/write/bulk[s] should operate on exactly 1 local index but was 2"
        }
      }
    },
    {
      "index" : {
        "_index" : "my-data",
        "_type" : "data",
        "_id" : "1",
        "status" : 500,
        "error" : {
          "type" : "illegal_state_exception",
          "reason" : "Action indices:data/write/bulk[s] should operate on exactly 1 local index but was 2"
        }
      }
    }
  ]
}

ES does not produce any logs with default logging level.

with 5.5.2 the script works as expected and the bulk writes return 200 level statuses

[jasontedor]

This issue is an X-Pack issue, it happens inside the authorization service for bulk requests. We only handle open source issues here. May I ask you to please open a topic on the forum in the X-Pack category where we handle closed source issues (you can link to that topic from here)?