# Issue with \_prefer\_nodes behavior in Elasticsearch 8.15.1

**URL:** <https://discuss.elastic.co/t/issue-with-prefer-nodes-behavior-in-elasticsearch-8-15-1/373125>\
**Category:** Elasticsearch\
**Created:** [January 13, 2025, 1:49pm UTC](https://discuss.elastic.co/t/issue-with-prefer-nodes-behavior-in-elasticsearch-8-15-1/373125 "2025-01-13T13:49:24Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![GabM](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/gabm/32/140628_2.png) [@GabM](https://discuss.elastic.co/u/GabM)\
**Post date:** [January 13, 2025, 1:49pm UTC](https://discuss.elastic.co/t/issue-with-prefer-nodes-behavior-in-elasticsearch-8-15-1/373125/1 "2025-01-13T13:49:24Z")

</div>

Hello,

I am encountering what seems to be unexpected behavior with the `preference` option in the `/_search` API when using the `_prefer_nodes` value. Here's the setup and the problem:

# Cluster Configuration:

- Elasticsearch version: 8.15.1
- The cluster is configured across three zones: `eu1`, `eu2`, and `eu3`.
- Each index is configured so that every shard exists in all zones:

```auto
curl -XPUT -u "$ESU" -H 'Content-Type: application/json' "$ES/*/_settings" -d '{
  "number_of_replicas": 2
}'

```

- Each node is assigned its respective zone using a node attribute:

```auto
cluster.routing.allocation.awareness.attributes: "zone"
cluster.routing.allocation.awareness.force.zone.values: eu1,eu2,eu3
node.attr.zone: eu1 # or eu2, eu3 depending on the zone

```

# What Works:

When I perform a `/_search` query with `preference=_only_nodes:zone:eu1`, it works as expected. Only the nodes in `eu1` respond to the query.

Example:

```auto
curl -sXGET -H 'Content-Type: application/json' -u "$ESU" "$ES/tmp_test/_search?preference=_only_nodes:zone:eu1" -d '{
  "explain": true,
  "query": {
    "match_all": {}
  }
}'

```

✅ Result: The query is handled exclusively by nodes in the `eu1` zone.

# What Doesn't Work:

When I perform a `/_search` query with `preference=_prefer_nodes:zone:eu1`, nodes from other zones (`eu2`, `eu3`) also respond to the query, even though the data is available on nodes in `eu1`.

Example:

```auto
curl -sXGET -H 'Content-Type: application/json' -u "$ESU" "$ES/tmp_test/_search?preference=_prefer_nodes:zone:eu1" -d '{
  "explain": true,
  "query": {
    "match_all": {}
  }
}'

```

❌ Result: Nodes from zones `eu2` and `eu3` respond alongside nodes from `eu1`, contrary to the expected behavior.

# Expected Behavior:

From the documentation, my understanding is that using `_prefer_nodes` should prioritize nodes in the specified attribute (in this case, `eu1`) while only falling back to others if necessary (e.g., if the data is not available in `eu1`).

Since the data exists on nodes in `eu1`, I would expect only nodes from `eu1` to handle the query.

# Question:

Is this the intended behavior of `_prefer_nodes`, or is it potentially a bug ?  
Are there additional settings or considerations I might have overlooked in configuring this feature?

Thank you for your help! Let me know if I can provide more details or logs to assist with troubleshooting.

# EDIT:

When I use `_prefer_nodes` but specify the node IDs directly (instead of using the `zone` attribute), it also works as expected, prioritizing the specified nodes.

Example:

```auto
curl -X GET -H 'Content-Type: application/json' -u "$ESU" "$ES/tmp_test/_search?preference=_prefer_nodes:2LS8vyq9TCGV-sS2RgkA9w,YnYSGPPaTHOCT0GHUQN9nw" -d '{
  "explain": true,
  "query": {
    "match_all": {}
  }
}'

```