# OpenSearch — Amazon OpenSearch Service

Domains are control-plane records only: no search cluster is started, so
`DomainStatus.Endpoint` names a host that answers nothing.

**Status:** ⚠️ Partial

## Quick start

```bash
export AWS_ENDPOINT_URL=http://localhost:4566

aws opensearch create-domain \
  --domain-name logs \
  --engine-version OpenSearch_2.11
aws opensearch describe-domain --domain-name logs
aws opensearch list-domain-names
```

Any credentials work; with none configured, run `eval "$(overcast env)"` first
— see [Using AWS SDKs and CLI](/docs/sdk-cli/index.md#credentials).

## What works

| Area | Behaviour |
| --- | --- |
| Domains | Create, describe, batch-describe, list and delete; active the moment they are created |
| Name collisions | A repeat domain name in the same region is rejected |
| Input validation | `DomainName` (3-28 characters of `[a-z][a-z0-9-]`) and `EngineVersion` (`OpenSearch_X.Y` or `Elasticsearch_X.Y`) are checked, as AWS checks them |
| Regions | Domains are per-region — the same name in two regions is two domains |
| Filtering | `ListDomainNames --engine-type` is honoured, derived from each domain's `EngineVersion` |
| Tags | Inline `TagList` at creation, plus `AddTags`, `ListTags` and `RemoveTags`; deleting a domain deletes its tags |

## Differences from AWS

| Area                  | On AWS                                                            | Overcast                                                                                                                                                |
| --- | --- | --- |
| The cluster | Indexes documents and serves queries | Nothing is indexed or queried; the domain endpoint is a name, not a service |
| `DomainStatus` | The full shape | The four required members plus `EngineVersion`, `Endpoint` and the `Created`/`Deleted`/`Processing` flags; the rest is omitted |
| Cluster settings | Configure the cluster | `ClusterConfig` is echoed back unchanged; `EBSOptions`, `VPCOptions`, access policies and the other ~25 `CreateDomain` members are accepted and ignored |
| `Endpoint` | A live domain host on port 443 | An AWS-shaped hostname that nothing answers on |
| Configuration changes | `UpdateDomainConfig`, upgrades, package association and auto-tune | Not implemented |
| Cross-cluster search | Outbound and inbound connections | Not modelled |

## Gotchas

> [!WARNING]
> Client libraries that talk the OpenSearch REST API (index, search, bulk)
> address the domain endpoint directly, not this control plane. Those calls
> reach nothing here — run a real OpenSearch container alongside Overcast if
> your test needs to index documents.

`DomainStatus.Endpoint` is a bare hostname, the way AWS reports one, and a
domain's data plane lives on that host rather than on a path beneath the
control-plane endpoint. There is no prefix to point a search client at: the
management operations above are the whole of what Overcast serves.

<!-- BEGIN overcast:capabilities -->

## Operations

All 8 listed operations are implemented.
Per-operation status, notes and AWS API links: [OpenSearch operations](/docs/services/opensearch/operations/index.md).

<!-- END overcast:capabilities -->

## Related

- [All service pages](/docs/services/index.md)
- [Service names and state overrides](/docs/configuration/index.md#service-names)
- [AWS API reference](https://docs.aws.amazon.com/opensearch-service/latest/APIReference/)