[Feature Request] API Models for hot and warm tiering actions

### Is your feature request related to a problem? Please describe

This task is to capture the API models needed for capturing the Tiering API (such as hot to warm, warm to hot), status APIs and cancel APIs.  

### Describe the solution you'd like

REST API Specification for Hot↔Warm Tiering

### 1. `POST /{index}/_tier/warm` — Initiate Hot→Warm Tiering

Description: Initiates tiering of an index from the hot tier to the warm tier. This is a cluster-manager-level operation that triggers shard relocation from hot nodes to warm nodes.

**Path Parameters:**

| Parameter | Type | Required | Description |
|-----------|------|----------|-------------|
| `index` | string | Yes | Name of the index to tier. Must be a single index (no wildcards, no comma-separated lists). Must not be on the migration blocklist. |

**Query Parameters:**

| Parameter | Type | Required | Default | Description |
|-----------|------|----------|---------|-------------|
| `timeout` | time | No | `30s` | Timeout for acknowledgement of the tiering request. |
| `cluster_manager_timeout` | time | No | `30s` | Timeout for connecting to the cluster manager node. |

Request Body: None

Success Response (200):
```
{
    "acknowledged": true
}
```
Failure Response (4xx/5xx):
```
{
    "error": {
        "root_cause": [
            {
                "type": "tiering_rejection_exception",
                "reason": "<rejection reason>"
            }
        ],
        "type": "tiering_rejection_exception",
        "reason": "<rejection reason>"
    },
    "status": 400
}
```

Validations:

1. Index name cannot be null or empty
2. Exactly one index must be specified (no multi-index support)
3. Index must not be on the migration blocklist
4. Cluster must not have global METADATA_WRITE, CREATE_INDEX, or WRITE blocks


### 2. `POST /{index}/_tier/hot` — Initiate Warm→Hot Tiering

Description: Initiates tiering of an index from the warm tier back to the hot tier. Triggers shard relocation from warm nodes to hot nodes.


**Path Parameters:**

| Parameter | Type | Required | Description |
|-----------|------|----------|-------------|
| `index` | string | Yes | Name of the index to tier. Must be a single index. Must not be on the migration blocklist. |

**Query Parameters:**

| Parameter | Type | Required | Default | Description |
|-----------|------|----------|---------|-------------|
| `timeout` | time | No | `30s` | Timeout for acknowledgement of the tiering request. |
| `cluster_manager_timeout` | time | No | `30s` | Timeout for connecting to the cluster manager node. |

Request Body: None

Success Response (200):

```
{
    "acknowledged": true
}
```

Failure Response (4xx/5xx):
```
{
    "error": {
        "root_cause": [
            {
                "type": "tiering_rejection_exception",
                "reason": "<rejection reason>"
            }
        ],
        "type": "tiering_rejection_exception",
        "reason": "<rejection reason>"
    },
    "status": 400
}
```
Validations: Same as Hot→Warm tiering.

---

### 3. `POST /_tier/_cancel/{index}` — Cancel Tiering Operation

Description: Cancels an in-progress tiering operation for an index. Useful for recovering from tiering operations stuck in RUNNING_SHARD_RELOCATION state.


**Path Parameters:**

| Parameter | Type | Required | Description |
|-----------|------|----------|-------------|
| `index` | string | Yes | Name of the index for which to cancel the in-progress tiering operation. Must be a single index. Must not be on the migration blocklist. |

**Query Parameters:**

| Parameter | Type | Required | Default | Description |
|-----------|------|----------|---------|-------------|
| `timeout` | time | No | `30s` | Timeout for acknowledgement of the cancel request. |
| `cluster_manager_timeout` | time | No | `30s` | Timeout for connecting to the cluster manager node. |

Success Response (200):

```
{
    "acknowledged": true
}
```

Failure Response (4xx/5xx):
```
{
    "error": {
        "root_cause": [
            {
                "type": "illegal_argument_exception",
                "reason": "<validation error>"
            }
        ],
        "type": "illegal_argument_exception",
        "reason": "<validation error>"
    },
    "status": 400
}
```

Validations:

1. Index name cannot be null or empty
2. Exactly one index must be specified
3. Index must not be on the migration blocklist
---

### 4. `GET /{index}/_tier` — Get Tiering Status for a Specific Index

**Path Parameters:**

| Parameter | Type | Required | Description |
|-----------|------|----------|-------------|
| `index` | string | Yes | Name of the index. Must be a single index (no wildcards). |

**Query Parameters:**

| Parameter | Type | Required | Default | Description |
|-----------|------|----------|---------|-------------|
| `detailed` | boolean | No | `false` | When `true`, includes per-shard relocation details (`source_shard_id`, `relocating_node_id`). |

Success Response (200) — Default (detailed=false):
```
{
    "tiering_status": {
        "index": "my-index",
        "state": "RUNNING_SHARD_RELOCATION",
        "source": "hot",
        "target": "warm",
        "start_time": 1719446400000,
        "shard_level_status": {
            "total": 10,
            "succeeded": 4,
            "running": 3,
            "pending": 3
        }
    }
}
```

Success Response (200) — With detailed=true:
```
{
    "tiering_status": {
        "index": "my-index",
        "state": "RUNNING_SHARD_RELOCATION",
        "source": "hot",
        "target": "warm",
        "start_time": 1719446400000,
        "shard_level_status": {
            "total": 10,
            "succeeded": 4,
            "running": 3,
            "pending": 3,
            "shard_relocation_status": [
                {
                    "source_shard_id": 2,
                    "relocating_node_id": "node-abc-123"
                },
                {
                    "source_shard_id": 5,
                    "relocating_node_id": "node-def-456"
                },
                {
                    "source_shard_id": 7,
                    "relocating_node_id": "node-ghi-789"
                }
            ]
        }
    }
}
```

**Top-Level Response Fields:**

| Field | Type | Description |
|-------|------|-------------|
| `tiering_status` | object | Root object containing the tiering status for the requested index. |

**`tiering_status` Object Fields:**

| Field | Type | Description |
|-------|------|-------------|
| `index` | string | Name of the index. |
| `state` | string | Current tiering state (e.g., `RUNNING_SHARD_RELOCATION`). |
| `source` | string | Source tier (`hot` or `warm`). |
| `target` | string | Target tier (`hot` or `warm`). |
| `start_time` | long | Epoch milliseconds when the tiering operation started. |
| `shard_level_status` | object | Shard-level progress counters and optional relocation details. |

**`shard_level_status` Object Fields:**

| Field | Type | Condition | Description |
|-------|------|-----------|-------------|
| `total` | int | Always | Total number of shards in the index. |
| `succeeded` | int | Always | Shards that have completed relocation and are `STARTED` on a target-tier node. |
| `running` | int | Always | Shards currently in `RELOCATING` state. |
| `pending` | int | Always | Shards that are `UNASSIGNED` or `STARTED` but still on a source-tier node. |
| `shard_relocation_status` | array | Only when `detailed=true` | Per-shard relocation details for shards in `RELOCATING` state. |

**`shard_relocation_status[]` Array Element Fields:**

| Field | Type | Description |
|-------|------|-------------|
| `source_shard_id` | int | The shard ID being relocated. |
| `relocating_node_id` | string | The node ID the shard is relocating to. |


Shard State Mapping:

succeeded: Shard is STARTED and placed on a node matching the target tier
running: Shard is in RELOCATING state
pending: Shard is UNASSIGNED or STARTED but still on a source-tier node

Failure Response (4xx):

```
{
    "error": {
        "root_cause": [
            {
                "type": "illegal_argument_exception",
                "reason": "request should contain single index"
            }
        ],
        "type": "illegal_argument_exception",
        "reason": "request should contain single index"
    },
    "status": 400
}
```
---

### 5. `GET /_tier/all` — List All In-Progress Tiering Operations

**Path Parameters:** None

**Query Parameters:**

| Parameter | Type | Required | Default | Description |
|-----------|------|----------|---------|-------------|
| `target` | string | No | None (returns all) | Filter by target tier. Valid values: `_warm`, `_hot`. |
| `v` | boolean | No | `false` | Verbose mode — includes column headers in tabular output. |
| `format` | string | No | `text` | Response format: `text` (tabular), `json`, `yaml`, etc. |

Request Body: None

Success Response (200) — Default (text/tabular):

```
index         state                     source target
my-index-1    RUNNING_SHARD_RELOCATION  hot    warm
my-index-2    RUNNING_SHARD_RELOCATION  warm   hot
my-index-3    RUNNING_SHARD_RELOCATION  hot    warm
```

Success Response (200) — With format=json:
```
[
    {
        "index": "my-index-1",
        "state": "RUNNING_SHARD_RELOCATION",
        "source": "hot",
        "target": "warm"
    },
    {
        "index": "my-index-2",
        "state": "RUNNING_SHARD_RELOCATION",
        "source": "warm",
        "target": "hot"
    }
]
```

**Response Fields (per entry):**

| Field | Type | Description |
|-------|------|-------------|
| `index` | string | Name of the index undergoing tiering. |
| `state` | string | Current tiering state (e.g., `RUNNING_SHARD_RELOCATION`). |
| `source` | string | Source tier (`hot` or `warm`). |
| `target` | string | Target tier (`hot` or `warm`). |


### Related component

Storage

### Describe alternatives you've considered

_No response_

### Additional context

Reference: https://github.com/opensearch-project/OpenSearch/issues/21016

Contributors: @skumawat2025  @abhita 

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[Feature Request] API Models for hot and warm tiering actions #21078

Is your feature request related to a problem? Please describe

Describe the solution you'd like

1. `POST /{index}/_tier/warm` — Initiate Hot→Warm Tiering

2. `POST /{index}/_tier/hot` — Initiate Warm→Hot Tiering

3. `POST /_tier/_cancel/{index}` — Cancel Tiering Operation

4. `GET /{index}/_tier` — Get Tiering Status for a Specific Index

5. `GET /_tier/all` — List All In-Progress Tiering Operations

Related component

Describe alternatives you've considered

Additional context

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Parameter	Type	Required	Default	Description
`timeout`	time	No	`30s`	Timeout for acknowledgement of the tiering request.
`cluster_manager_timeout`	time	No	`30s`	Timeout for connecting to the cluster manager node.

Field	Type	Description
`index`	string	Name of the index.
`state`	string	Current tiering state (e.g., `RUNNING_SHARD_RELOCATION`).
`source`	string	Source tier (`hot` or `warm`).
`target`	string	Target tier (`hot` or `warm`).
`start_time`	long	Epoch milliseconds when the tiering operation started.
`shard_level_status`	object	Shard-level progress counters and optional relocation details.

Field	Type	Condition	Description
`total`	int	Always	Total number of shards in the index.
`succeeded`	int	Always	Shards that have completed relocation and are `STARTED` on a target-tier node.
`running`	int	Always	Shards currently in `RELOCATING` state.
`pending`	int	Always	Shards that are `UNASSIGNED` or `STARTED` but still on a source-tier node.
`shard_relocation_status`	array	Only when `detailed=true`	Per-shard relocation details for shards in `RELOCATING` state.

Field	Type	Description
`source_shard_id`	int	The shard ID being relocated.
`relocating_node_id`	string	The node ID the shard is relocating to.

Parameter	Type	Required	Default	Description
`target`	string	No	None (returns all)	Filter by target tier. Valid values: `_warm`, `_hot`.
`v`	boolean	No	`false`	Verbose mode — includes column headers in tabular output.
`format`	string	No	`text`	Response format: `text` (tabular), `json`, `yaml`, etc.

Field	Type	Description
`index`	string	Name of the index undergoing tiering.
`state`	string	Current tiering state (e.g., `RUNNING_SHARD_RELOCATION`).
`source`	string	Source tier (`hot` or `warm`).
`target`	string	Target tier (`hot` or `warm`).

[Feature Request] API Models for hot and warm tiering actions #21078

Description

Is your feature request related to a problem? Please describe

Describe the solution you'd like

1. POST /{index}/_tier/warm — Initiate Hot→Warm Tiering

2. POST /{index}/_tier/hot — Initiate Warm→Hot Tiering

3. POST /_tier/_cancel/{index} — Cancel Tiering Operation

4. GET /{index}/_tier — Get Tiering Status for a Specific Index

5. GET /_tier/all — List All In-Progress Tiering Operations

Related component

Describe alternatives you've considered

Additional context

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

1. `POST /{index}/_tier/warm` — Initiate Hot→Warm Tiering

2. `POST /{index}/_tier/hot` — Initiate Warm→Hot Tiering

3. `POST /_tier/_cancel/{index}` — Cancel Tiering Operation

4. `GET /{index}/_tier` — Get Tiering Status for a Specific Index

5. `GET /_tier/all` — List All In-Progress Tiering Operations