# LaunchDarkly Server-Side SDK for Node.js - DynamoDB integration

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This library provides a DynamoDB-backed persistence mechanism (feature store) for the [LaunchDarkly Node.js SDK](https://github.com/launchdarkly/js-core/packages/sdk/server-node), replacing the default in-memory feature store. It uses the AWS SDK for Node.js.
The minimum version of the LaunchDarkly Server-Side SDK for Node for use with this library is 8.0.0.

## LaunchDarkly overview

[LaunchDarkly](https://www.launchdarkly.com) is a feature management platform that serves over 100 billion feature flags daily to help teams build better software, faster. [Get started](https://docs.launchdarkly.com/home/getting-started) using LaunchDarkly today!

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## Supported Node versions

This package is compatible with Node.js versions 14 and above.

## Getting started

Refer to [Using DynamoDB as a persistent feature store](https://docs.launchdarkly.com/sdk/features/storing-data/dynamodb#nodejs-server-side).

## Quick setup

1. In DynamoDB, create a table which has the following schema: a partition key called "namespace" and a sort key called "key", both with a string type. The LaunchDarkly library does not create the table automatically, because it has no way of knowing what additional properties (such as permissions and throughput) you would want it to have.

2. Install this package with `npm` or `yarn`:

`npm install @launchdarkly/node-server-sdk-dynamodb --save`

3. If your application does not already have its own dependency on the `@aws-sdk/client-dynamodb` package, and if it will _not_ be running in AWS Lambda, add `@aws-sdk/client-dynamodb` as well:

`npm install @aws-sdk/client-dynamodb --save`

The `launchdarkly-node-server-sdk-dynamodb` package does not provide `@aws-sdk/client-dynamodb` as a transitive dependency, because it is provided automatically by the Lambda runtime and this would unnecessarily increase the size of applications deployed in Lambda. Therefore, if you are not using Lambda you need to provide `@aws-sdk/client-dynamodb` separately.

4. Import the package:

```typescript
const { DynamoDBFeatureStore } = require('launchdarkly-node-server-sdk-dynamodb');
```

5. When configuring your SDK client, add the DynamoDB feature store:

```typescript
const store = DynamoDBFeatureStore('YOUR TABLE NAME');
const config = { featureStore: store };
const client = LaunchDarkly.init('YOUR SDK KEY', config);
```

By default, the DynamoDB client will try to get your AWS credentials and region name from environment variables and/or local configuration files, as described in the AWS SDK documentation. You can also specify any valid [DynamoDB client options](https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/DynamoDB.html#constructor-property) like this:

```typescript
const dynamoDBOptions = {
  credentials: { accessKeyId: 'YOUR KEY', secretAccessKey: 'YOUR SECRET' },
};
const store = DynamoDBFeatureStore('YOUR TABLE NAME', { clientOptions: dynamoDBOptions });
```

Alternatively, if you already have a fully configured DynamoDB client object, you can tell LaunchDarkly to use that:

```typescript
const store = DynamoDBFeatureStore('YOUR TABLE NAME', {
  dynamoDBClient: myDynamoDBClientInstance,
});
```

6. If you are running a [LaunchDarkly Relay Proxy](https://github.com/launchdarkly/ld-relay) instance, or any other process that will pre-populate the DynamoDB table with feature flags from LaunchDarkly, you can use [daemon mode](https://github.com/launchdarkly/ld-relay#daemon-mode), so that the SDK retrieves flag data only from DynamoDB and does not communicate directly with LaunchDarkly. This is controlled by the SDK's `useLdd` option:

```typescript
const config = { featureStore: store, useLdd: true };
const client = LaunchDarkly.init('YOUR SDK KEY', config);
```

7. If the same DynamoDB table is being shared by SDK clients for different LaunchDarkly environments, set the `prefix` option to a different short string for each one to keep the keys from colliding:

```typescript
const store = DynamoDBFeatureStore('YOUR TABLE NAME', { prefix: 'env1' });
```

## Required permissions

The store reads and writes items with `dynamodb:Query`, `dynamodb:GetItem`, `dynamodb:PutItem`, and `dynamodb:BatchWriteItem`. It also uses `dynamodb:DeleteItem` to remove its initialized token before it rewrites the full dataset, so a partially written dataset is not treated as complete by other readers. If the credentials do not allow `dynamodb:DeleteItem`, the store logs a warning and initializes without that protection.

## Capacity planning

A full data write happens at SDK initialization and during a recovery write-back after a store outage. It writes every flag and segment once, which consumes about one write capacity unit per kilobyte of item data. The store keys all items of one data kind under a single partition key, so these writes concentrate on few partitions. When DynamoDB throttles a batch, the store retries it with jittered exponential backoff for up to ten attempts (up to about 26 seconds of delays per batch). If the table's provisioned write capacity is too low to drain a batch within that budget, the write fails, and a later recovery attempt rewrites the full data set. Provision enough write capacity for a full rewrite, or use on-demand capacity mode.

## Caching behavior

To reduce traffic to DynamoDB, there is an optional in-memory cache that retains the last known data for a configurable amount of time. This is on by default; to turn it off (and guarantee that the latest feature flag data will always be retrieved from DynamoDB for every flag evaluation), configure the store as follows:

```typescript
const factory = DynamoDBFeatureStore({ cacheTTL: 0 });
```

## Contributing

We encourage pull requests and other contributions from the community. Check out our [contributing guidelines](CONTRIBUTING.md) for instructions on how to contribute to this SDK.

## Verifying SDK build provenance with the SLSA framework

LaunchDarkly uses the [SLSA framework](https://slsa.dev/spec/v1.0/about) (Supply-chain Levels for Software Artifacts) to help developers make their supply chain more secure by ensuring the authenticity and build integrity of our published SDK packages. To learn more, see the [provenance guide](PROVENANCE.md).

## About LaunchDarkly

- LaunchDarkly is a continuous delivery platform that provides feature flags as a service and allows developers to iterate quickly and safely. We allow you to easily flag your features and manage them from the LaunchDarkly dashboard. With LaunchDarkly, you can:
  - Roll out a new feature to a subset of your users (like a group of users who opt-in to a beta tester group), gathering feedback and bug reports from real-world use cases.
  - Gradually roll out a feature to an increasing percentage of users, and track the effect that the feature has on key metrics (for instance, how likely is a user to complete a purchase if they have feature A versus feature B?).
  - Turn off a feature that you realize is causing performance problems in production, without needing to re-deploy, or even restart the application with a changed configuration file.
  - Grant access to certain features based on user attributes, like payment plan (eg: users on the ‘gold’ plan get access to more features than users in the ‘silver’ plan).
  - Disable parts of your application to facilitate maintenance, without taking everything offline.
- LaunchDarkly provides feature flag SDKs for a wide variety of languages and technologies. Check out [our documentation](https://docs.launchdarkly.com/sdk) for a complete list.
- Explore LaunchDarkly
  - [launchdarkly.com](https://www.launchdarkly.com/ 'LaunchDarkly Main Website') for more information
  - [docs.launchdarkly.com](https://docs.launchdarkly.com/ 'LaunchDarkly Documentation') for our documentation and SDK reference guides
  - [apidocs.launchdarkly.com](https://apidocs.launchdarkly.com/ 'LaunchDarkly API Documentation') for our API documentation
  - [blog.launchdarkly.com](https://blog.launchdarkly.com/ 'LaunchDarkly Blog Documentation') for the latest product updates

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