> For the complete documentation index, see [llms.txt](https://mercure-technologies.gitbook.io/expo-open-ota/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mercure-technologies.gitbook.io/expo-open-ota/caching/redis.md).

# Redis

Use Redis to share cached data across server replicas.

Redis is required for multi-replica deployments. It keeps manifests and metrics consistent.

### Configure Redis

Set `CACHE_MODE` to `redis` and provide a Redis endpoint:

```dotenv
CACHE_MODE=redis
REDIS_HOST=your-redis-host
REDIS_PORT=your-redis-port
REDIS_PASSWORD=your-redis-password
```

`REDIS_USERNAME` is optional. Set it when your Redis server uses ACL authentication.

```dotenv
REDIS_USERNAME=your-redis-username
```

### Enable TLS

Set `REDIS_USE_TLS=true` when your Redis endpoint requires TLS:

```dotenv
REDIS_USE_TLS=true
```

For a custom certificate authority, add its base64-encoded PEM certificate:

```dotenv
REDIS_CA_CERT_B64=base64-encoded-ca-certificate
```

Generate this value with:

```shellscript
base64 -i certificate.pem | tr -d '\n'
```

{% hint style="info" %}
Use `REDIS_PASSWORD` with the matching `REDIS_USERNAME` for ACL authentication.
{% endhint %}

### Redis Sentinel

Set `CACHE_MODE=redis-sentinel` for high availability with automatic master failover:

```dotenv
CACHE_MODE=redis-sentinel
REDIS_SENTINEL_ADDRS=sentinel-0:26379,sentinel-1:26379,sentinel-2:26379
REDIS_SENTINEL_MASTER_NAME=mymaster
```

`REDIS_SENTINEL_ADDRS` is a comma-separated list of Sentinel addresses. At least one address is required.

`REDIS_SENTINEL_MASTER_NAME` is optional. It defaults to `mymaster`.

The server discovers the current master through Sentinel. When Sentinel promotes a new master, the client reconnects transparently — no restart is needed.

`REDIS_PASSWORD`, `REDIS_USERNAME`, `REDIS_USE_TLS`, and `REDIS_CA_CERT_B64` apply to Sentinel mode as well.

### Choose an endpoint

The server connects to one standalone Redis endpoint, or to a Sentinel-monitored master with `CACHE_MODE=redis-sentinel`.

Redis Cluster is not supported.

For managed Redis, use the provider's primary endpoint. This includes ElastiCache, Memorystore, and Upstash.

### Isolate deployments

All keys use the `expoopenota` prefix by default. Set `CACHE_KEY_PREFIX` when deployments share Redis:

```dotenv
CACHE_KEY_PREFIX=production
```

Servers sharing Redis and a prefix read each other's cached entries. Use a unique prefix for each deployment.


---

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