> ## Documentation Index
> Fetch the complete documentation index at: https://docs.stigg.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Persistent cache

By default, the Node.js SDK and Sidecar store entitlements data in a local in-memory cache for fast and instant entitlement checks. If you restart the host process of the SDK or re-initialize the SDK, the local cache data will be lost. Usually, this behavior is acceptable because if the entitlements data is missing, the SDK will fetch it from the Stigg API over the network.

Alternatively, you can provide an external store to persist the customer entitlements data which can survive restarts and be accessed by multiple processes. If your application is a fleet consisting of dozens of servers, or if you have a serverless infrastructure where each process is transient and can be de-provisioned after a limited period of time, a persistent cache can significantly reduce cache misses.

Stigg offers a persistent cache setup for backend SDK users (currently supported in the [Node SDK](/api-and-sdks/integration/backend/nodejs) and [Sidecar](/api-and-sdks/integration/backend/sidecar)), providing several advantages over in-memory cache for high-scale services:

* Redundancy - data is available on your Redis cluster even in case of an API outage
* Low latency — including **\< 10ms** credit balance retrieval via `getCreditEntitlement()`
* Fewer requests from your services to the Stigg API
* Reduce the memory footprint of the SDK in your services
* Reducing cache coherence issues
* Increased cache hits/misses ratio

To enable persistent cache in your environment, please [contact the Stigg Support Team](mailto:support@stigg.io).

## Overview

Stigg's persistent cache relies on a running [persistent-cache-service](https://gallery.ecr.aws/p2i1w6c0/persistent-cache-service) as part of your app deployment process. The service connects to a dedicated AWS SQS queue (owned and managed by Stigg), consumes messages that carry the state changes from the originating environment, and keeps your Redis cache instance with up-to-date data. The service can be scaled horizontally to keep up with the rate of arriving messages. In case of a cache miss, the SDK will fetch the data over the network directly from API, and update the cache to serve future requests.

<img src="https://mintcdn.com/stigg/_E1NPxWRKvYZ5hDE/images/docs/837f6c0-image.png?fit=max&auto=format&n=_E1NPxWRKvYZ5hDE&q=85&s=6c02f9c8330f2b1fb1ed6adea07295e3" alt="" width="1083" height="576" data-path="images/docs/837f6c0-image.png" />

## Running the service

In order for the persistent cache to be updated properly in near real-time, you'll need to install and run at least one instance of [persistent-cache-service](https://gallery.ecr.aws/p2i1w6c0/persistent-cache-service).

<Warning>
  **Version 3.0.0 breaking change**: persistent-cache-service v3.0.0 introduces a new Redis data structure for credit entitlements. Once v3.0.0 writes data to Redis, older SDK/sidecar versions will return incorrect entitlement data.

  **You must upgrade in this order:**

  1. Upgrade `@stigg/node-server-sdk` to v4.12.1+ or sidecar-service to v5.194.5+
  2. Deploy all updated SDK/sidecar instances
  3. Only then deploy persistent-cache-service v3.0.0

  See the [persistent-cache-service changelog](/api-and-sdks/changelog/backend-graphql/persistent-cache) for details.
</Warning>

### Prerequisites

* An SQS provisioned by Stigg, to consume messages originating from your environment
* Redis cluster to persist entitlements and usage for a future read operation

### Usage

Run the service, replacing `<tag>` with the latest version in the [ECR Public Gallery](https://gallery.ecr.aws/stigg/persistent-cache-service):

<Note>
  Starting from version **2.37.0**, the service uses IAM role-based authentication for SQS access. `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY` are no longer required — the service will automatically use the IAM role attached to the host (EC2 instance, ECS task, EKS pod, etc.).
</Note>

<CodeGroup>
  ```shell shell theme={null}
  docker run --publish=4000:4000 \
    --name stigg-persistent-cache \
    -e AWS_REGION="us-east-2" \
    -e QUEUE_URL="https://sqs.us-east-2.amazonaws.com/..." \
    -e REDIS_HOST="host.docker.internal" \
    -e SERVER_API_KEY="<FULL_ACCESS_KEY>" \
    -e ENVIRONMENT_PREFIX="development" \
    public.ecr.aws/stigg/persistent-cache-service:<tag>
  ```
</CodeGroup>

Available options:

| Environment Variable  | Type         | Default                                                | Description                                                                                                                   |
| --------------------- | ------------ | ------------------------------------------------------ | ----------------------------------------------------------------------------------------------------------------------------- |
| AWS\_REGION           | **String\*** |                                                        | The AWS region of the SQS queue                                                                                               |
| QUEUE\_URL            | **String\*** |                                                        | The URL of the queue to consume from                                                                                          |
| SERVER\_API\_KEY      | **String\*** |                                                        | Environment's full access key                                                                                                 |
| ENVIRONMENT\_PREFIX   | String       | production                                             | The Identifier of the environment needs to be the same as the one used by the SDK                                             |
| REDIS\_HOST           | String       |                                                        | Redis host address                                                                                                            |
| REDIS\_PORT           | Number       | 6379                                                   | Redis port                                                                                                                    |
| REDIS\_DB             | Number       | 0                                                      | Redis DB identifier                                                                                                           |
| REDIS\_USERNAME       | String       |                                                        | (Optional) Redis username                                                                                                     |
| REDIS\_PASSWORD       | String       |                                                        | (Optional) Redis password                                                                                                     |
| REDIS\_TLS            | Boolean      | 0                                                      | (Optional) Redis use TLS encryption                                                                                           |
| BATCH\_SIZE           | Number       | 1                                                      | Number of messages to receive in a single batch                                                                               |
| KEYS\_TTL\_IN\_SECS   | Number       | 604800 (7 days)                                        | The duration in milliseconds that data will be kept in the cache before evicted                                               |
| EDGE\_API\_URL        | String       | [https://edge.api.stigg.io](https://edge.api.stigg.io) | Edge API address URL                                                                                                          |
| SENTRY\_DSN           | String       | Loaded from remote                                     | Sentry DSN used for internal error reporting                                                                                  |
| DISABLE\_SENTRY       | Boolean      | 0                                                      | Disables reporting internal errors to Sentry                                                                                  |
| PORT                  | Number       | 4000                                                   | HTTP server port                                                                                                              |
| CACHE\_UPDATE\_POLICY | String       | `UPDATE_IF_EXISTS`                                     | Enum, can be either `UPSERT` (always write new data to cache) or `UPDATE_IF_EXISTS` (update only if the data already exists). |
| LOG\_LEVEL            | String       | `info`                                                 | Log level, can be one of: `error`, `warn`, `info`, `debug`.                                                                   |
| LOG\_MESSAGE\_KEY     | String       | `msg`                                                  | Log string key for the `message` in the JSON object.                                                                          |
| LOG\_ERROR\_KEY       | String       | `err`                                                  | Log string key for the `error` in the JSON object.                                                                            |

\*Required fields

## Health

The service exposes the following HTTP endpoints:

### `GET /livez`

Returns `200` if the service is alive.

Healthy response: `{"status":"UP"}`

### `GET /readyz`

Returns `200` if the service is ready to receive messages.

Healthy response: `{ "status": "UP", "consumers": 10, "redis": "CONNECTED" }`

Unhealthy response: `{ "status": "DOWN", "consumers": 0, "redis": "DISCONNECTED" }`

### `GET /metrics`

Returns service metrics in [Prometheus](https://prometheus.io/) format.

This endpoint includes both system-level and cache specific metrics. These metrics are helpful for monitoring the health and performance of the service.

| Metric Name                                                                                      | Type      | Description                                                |
| ------------------------------------------------------------------------------------------------ | --------- | ---------------------------------------------------------- |
| <span style={{whiteSpace: "nowrap"}}>`persistent_cache_write_duration_seconds`</span>            | histogram | Time taken to write to Redis cache                         |
| <span style={{whiteSpace: "nowrap"}}>`persistent_cache_write_errors_total`</span>                | counter   | Number of failed Redis cache write operations              |
| <span style={{whiteSpace: "nowrap"}}>`persistent_cache_hit_ratio`</span>                         | gauge     | Percentage of Redis cache hits vs total cache queries      |
| <span style={{whiteSpace: "nowrap"}}>`persistent_cache_memory_usage_bytes`</span>                | gauge     | Amount of memory used by the Redis cache in bytes          |
| <span style={{whiteSpace: "nowrap"}}>`persistent_cache_hits_total`</span>                        | gauge     | Total number of cache hits in Redis                        |
| <span style={{whiteSpace: "nowrap"}}>`persistent_cache_misses_total`</span>                      | gauge     | Total number of cache misses in Redis                      |
| <span style={{whiteSpace: "nowrap"}}>`persistent_cache_message_handling_duration_seconds`</span> | histogram | Time taken to process a message from receipt to completion |
| <span style={{whiteSpace: "nowrap"}}>`persistent_cache_messages_processed_total`</span>          | counter   | Total number of messages processed                         |

## Configure the SDK

To configure the SDK to use the Redis cache, provide the `redis` config during initialization:

<CodeGroup>
  ```javascript Node.js theme={null}
  const stigg = Stigg.initialize({
      apiKey: '<SERVER_API_KEY>',
      redis: {
          host: 'localhost', 
          port: '6379',
          db: 0, // optionally, the db number to use
          environmentPrefix: 'production', // a string, for example 'production', 'staging' & etc
      }
  });
  ```
</CodeGroup>

<Warning>
  Please make sure that the SDK and the `persistent-cache-service` are configured to use the same Redis instance, DB number, and the same **environment prefix**.
</Warning>

During initialization, the SDK will try to connect to the Redis instance. Once connected, all the entitlement checks will be evaluated against data from the persistent cache instead of fetching it over the network.

The persistent cache is updated the same way the in-memory cache does - if customer data is missing, it will be fetched over the network and persisted in the cache.

## Deploying the Service in Kubernetes

You can install the Service using either `helm` or `kustomize`. For detailed instructions, resources, and examples, visit our [GitHub repository](https://github.com/stiggio/stigg-helm-charts).

## Benchmarks

Based on internal benchmarks, a single instance of the `persistent-cache-service` runs efficiently with the following configuration:

* **CPU and memory**: 1 vCPU and 512MB RAM.
* **CPU usage**: Averages around 60%, with a range between 30% and 90% under constant load (i.e., when messages are consistently present in the queue).
* **Memory footprint**: Approximately 250MB.
* **Throughput**: Handles up to 100 messages per second, depending on message type and processing complexity.
* **Storage**: Does not use any disk storage. The minimal container image size is sufficient.
* **Scalability**: The service is stateless and can be horizontally scaled as needed to meet higher throughput demands.