Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

[Backport 2.17] Improved shard allocation awareness attributes documentation #8338

Merged
merged 1 commit into from
Sep 18, 2024
Merged

[Backport 2.17] Improved shard allocation awareness attributes documentation #8338

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
20 changes: 18 additions & 2 deletions _tuning-your-cluster/index.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -192,11 +192,25 @@ To better understand and monitor your cluster, use the [CAT API]({{site.url}}{{s
## (Advanced) Step 6: Configure shard allocation awareness or forced awareness
To further fine-tune your shard allocation, you can set custom node attributes for shard allocation awareness or forced awareness.
### Shard allocation awareness
If your nodes are spread across several geographical zones, you can configure shard allocation awareness to allocate all replica shards to a zone that’s different from their primary shard.
You can set custom node attributes on OpenSearch nodes to be used for shard allocation awareness. For example, you can set the `zone` attribute on each node to represent the zone in which the node is located. You can also use the `zone` attribute to ensure that the primary shard and its replica shards are allocated in a balanced manner across available, distinct zones. For example, maximum shard copies per zone would equal `ceil (number_of_shard_copies/number_of_distinct_zones)`.
Shard allocation awareness attempts to separate primary and replica shards across multiple zones because 2 shard copies cannot be placed on the same node. When only 1 zone is available, such as after a zone failure, OpenSearch allocates replica shards to the only remaining zone. For example, if your index has a total of 5 shard copies (1 primary and 4 replicas) and nodes in 3 distinct zones, then OpenSearch will perform the following to allocate all 5 shard copies:
- Allocate fewer than 2 shards per zone, which will require at least 2 nodes in 2 zones.
- Allocate the last shard in the third zone, with at least 1 node needed in the third zone.
Alternatively, if you have 3 nodes in the first zone and 1 node in each remaining zone, then OpenSearch will allocate:
With shard allocation awareness, if the nodes in one of your zones fail, you can be assured that your replica shards are spread across your other zones. It adds a layer of fault tolerance to ensure your data survives a zone failure beyond just individual node failures.
- 2 shard copies in the first zone.
- 1 shard copy in the remaining 2 zones.
The final shard copy will remain unallocated due to the lack of nodes.
With shard allocation awareness, if the nodes in one of your zones fail, you can be assured that your replica shards are spread across your other zones, adding a layer of fault tolerance to ensure that your data survives zone failures.
To configure shard allocation awareness, add zone attributes to `opensearch-d1` and `opensearch-d2`, respectively:
Expand All @@ -219,6 +233,8 @@ PUT _cluster/settings
}
```

You can also use multiple attributes for shard allocation awareness by providing the attributes as a comma-separated string, for example, `zone,rack`.

You can either use `persistent` or `transient` settings. We recommend the `persistent` setting because it persists through a cluster reboot. Transient settings don't persist through a cluster reboot.

Shard allocation awareness attempts to separate primary and replica shards across multiple zones. However, if only one zone is available (such as after a zone failure), OpenSearch allocates replica shards to the only remaining zone.
Expand Down
Loading