doc(adr): elasticsearch scaling (#668)

Author: leoguillaume

.gitignore

@@ -218,4 +218,5 @@ compose.yml
 playground/.web
 playground/.states
 playground/.gitignore
-playground/requirements.txt
+playground/requirements.txt
+run.sh

adr/2026-01-30-es-scaling.md

@@ -0,0 +1,90 @@
+# ADR - 2026-01-30 - Elasticsearch Scaling
+
+**Status:** In Progress
+**Date:** 2026-01-30
+**Authors:** Development Team
+**Decision Outcome:** Merge Elasticsearch indices into a single index
+
+---
+
+## Context
+
+[WIP]
+
+## Migration script
+
+The [`adr/scripts/2026-01-30-es-migration.py`](adr/scripts/2026-01-30-es-migration.py) script is used to migrate the data from the source Elasticsearch indices to the destination Elasticsearch index.
+
+1. Clone the repository on the target server
+
+```bash
+git clone https://github.com/etalab-ia/OpenGateLLM.git && cd OpenGateLLM
+```
+
+2. Install the dependencies
+
+> [!NOTE]
+> We recommend to create a virtual environment and activate it before installing the dependencies.
+
+```bash
+pip install ".[api]"
+```
+
+3. Create the bash script to run the migration
+
+```bash
+touch run.sh
+```
+
+The script should look like this:
+
+```bash
+#!/bin/bash
+export PYTHONPATH=.
+export POSTGRES_URL=
+
+export SOURCE_ES_URL=
+export SOURCE_ES_USERNAME=
+export SOURCE_ES_PASSWORD= 
+
+export DESTINATION_ES_URL=
+export DESTINATION_ES_USERNAME=
+export DESTINATION_ES_PASSWORD=
+export DESTINATION_ES_INDEX_NAME=
+export DESTINATION_ES_VECTOR_SIZE=
+export DESTINATION_ES_NUMBER_OF_SHARDS=
+export DESTINATION_ES_NUMBER_OF_REPLICAS=
+export DESTINATION_ES_INDEX_LANGUAGE=
+
+python adr/scripts/2026-01-30-es-migration.py > migration.log 2>&1
+```
+
+The environment variables are:
+
+| Variable | Description | Example |
+|----------|-------------|-------------|
+| `POSTGRES_URL` | The URL of the PostgreSQL database. The URL must be in the format `postgresql+asyncpg://<username>:<password>@<host>:<port>/<database>`. | `postgresql+asyncpg://postgres:changeme@localhost:5432/postgres` |
+| `SOURCE_ES_URL` | The URL of the source Elasticsearch cluster must be in the format `http://<host>:<port>`. You can use the same Elastiscearch cluster for the source and destination. | `http://localhost:9200` |
+| `SOURCE_ES_USERNAME` | The username of the source Elasticsearch cluster. | `elasticsearch` |
+| `SOURCE_ES_PASSWORD` | The password of the source Elasticsearch cluster. | `changeme` |
+| `DESTINATION_ES_URL` | The URL of the destination Elasticsearch cluster must be in the format `http://<host>:<port>`. | `http://localhost:9200` |
+| `DESTINATION_ES_USERNAME` | The username of the destination Elasticsearch cluster. | `elasticsearch` |
+| `DESTINATION_ES_PASSWORD` | The password of the destination Elasticsearch cluster. | `changeme` |
+| `DESTINATION_ES_INDEX_NAME` | The name of the destination Elasticsearch index. By default, the index name is `opengatellm`, corresponds to the default index name in the configuration file. | `opengatellm` |
+| `DESTINATION_ES_VECTOR_SIZE` | The vector size corresponds to the dimension of the vector embedding used by the embeddings model setup in your configuration file (ex: `1024`). | `1024` |
+| `DESTINATION_ES_NUMBER_OF_SHARDS` | The number of shards of the destination Elasticsearch index, check Elasticsearch documentation to know the maximum number of shards per node. | `1` |
+| `DESTINATION_ES_NUMBER_OF_REPLICAS` | The number of replicas of the destination Elasticsearch index, check Elasticsearch documentation to know the maximum number of replicas per node. | `1` |
+| `DESTINATION_ES_INDEX_LANGUAGE` | The language of the destination Elasticsearch index. The supported languages are: `french`, `english`, `german`, `italian`, `portuguese`, `spanish`, `swedish`. | `french` |
+
+4. Run the script
+
+```bash
+./run.sh
+```
+
+The script will output the progress of the migration to the `migration.log` file. If script fails, you can rerun it, it will continue from the last point where it failed.
+
+5. Check the migration
+
+```bash
+cat migration.log