Elasticsearch version (bin/elasticsearch --version):

Version: 5.5.3, Build: 9305a5e/2017-09-07T15:56:59.599Z, JVM: 1.8.0_151

Plugins installed: []

JVM version (java -version):

java version "1.8.0_151"
Java(TM) SE Runtime Environment (build 1.8.0_151-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.151-b12, mixed mode)

OS version (uname -a if on a Unix-like system): Darwin Thiagos-MacBook-Pro.local 17.0.0 Darwin Kernel Version 17.0.0: Thu Aug 24 21:48:19 PDT 2017; root:xnu-4570.1.46~2/RELEASE_X86_64 x86_64

Description of the problem including expected versus actual behavior:

If a non-data node, that contains dangling indices in it's data path, joins a cluster these dangling indices will be detected and auto-imported.

IMO, a non-data node that contains index data in it's data path is probably accidental and unintended. In this case, those dangling indices should not be detected, better yet if the node does not even starts (maybe a bootstrap check that fails if a non-data node contains index data in it's data path).

Steps to reproduce:

This can be done in a single machine:

1. Start node-1 with bin/elasticsearch -E path.data=/Users/thiago/data-1 -E node.name=node-1
2. Start node-2 with bin/elasticsearch -E path.data=/Users/thiago/data-2 -E node.name=node-2
3. Create an index test configured with 1S/0R with curl -XPUT localhost:9200/test -d '{ "settings": { "index": { "number_of_shards": 1, "number_of_replicas": 0 } } }' -H "Content-Type: application/json"
4. Create a document curl -XPOST localhost:9200/test -d '{ "test": 1 }' -H "Content-Type: application/json"
5. Stop both nodes
6. Check which data directory, either data-1 or data-2, that the shard for index test was created in and delete the other empty data directory (so we effectively make a dangling index).
7. Consider that data-2 was deleted. So start node-2 again with bin/elasticsearch -E path.data=/Users/thiago/data-2 -E node.name=node-2
8. Start node-1 (which contains dangling indices) as a non-data node with bin/elasticsearch -E path.data=/Users/thiago/data-1 -E node.name=node-1 -E node.data=false

Provide logs (if relevant):

After non-data node node-1 starts, node-2 will detect and auto-import dangling indices even though node-1 is a non-data node:

[2017-10-21T18:02:14,158][INFO ][o.e.g.LocalAllocateDangledIndices] [node-2] auto importing dangled indices [[test/R2Nh9sERThmkJ-0IZ0ppwA]/OPEN] from [{node-1}{RqWMW2AeSXWOpkUm4cT1TA}{lEqpWLIhRqqU_n1DSFuv2Q}{127.0.0.1}{127.0.0.1:9301}]