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The Next DBC API

This is the API part of the next DBC graphql api. The application is built with Node.js and Express, and exposes a GraphQL API. The API is used by the frontend as the one and only entrance to underlying services.

Getting started

The development environment may be set up using npm.

npm

  • npm install installs dependencies.
  • cd website
  • npm install
  • cd ..
  • npm run dev starts a dev server.
  • npm test runs jest tests.

Notes on performance

A single query to the API typically leads to requests being sent to several underlying data sources. This is perfectly fine, and one of the strengths of GraphQL. But if data loading is not handled properly it results in an excessive number of network request round-trips.

We use DataLoader library (a port of Facebooks "Loader" API) and a Redis cache for mitigating these challenges.

  • Per request caching (DataLoader) DataLoader has a builtin memory cache, preventing multiple requests for the same resource from happening in the same GraphQL request.
  • Per request batching (DataLoader) Batching is the primary feature of DataLoader. It groups requests to the same resource and let us (if the data source supports it) fetch the data in a single request. Even though, a data source does not support batch requests it is still highly beneficial. As soon as data is in the Redis cache, we fetch it using a batch requests.
  • Global cache (Redis) We use a global Redis cache shared across all GraphQL instances.
  • Complex query analysis Queries are analyzed before execution, and if they are too complex they are rejected. These queries are typically highly nested, leading to a high number of requests to underlying data sources.

Environment Variables

The following environment variables can be set in the application

  • PORT Port on which the server runs. Default is 3000.
  • MOREINFO_URL URL on which moreinfo runs.
  • MOREINFO_USER The user.
  • MOREINFO_GROUP The group.
  • MOREINFO_PASSWORD The group.
  • MOREINFO_TIME_TO_LIVE_SECONDS Time for data to live in the Redis cache in seconds. Default is 86400.
  • MOREINFO_PREFIX The prefix to be used for keys in the Redis cache. This may be changed to invalidate entries. Default is moreinfo-1.
  • OPENFORMAT_URL The openformat URL. Default is http://openformat-php-master.frontend-prod.svc.cloud.dbc.dk/server.php
  • OPENFORMAT_TIME_TO_LIVE_SECONDS Time for data to live in the Redis cache in seconds. Default is 86400.
  • OPENFORMAT_PREFIX The prefix to be used for keys in the Redis cache. This may be changed to invalidate entries. Default is openformat-1.
  • REDIS_HOST The Redis host. Default is 127.0.0.1.
  • REDIS_PORT The Redis port. Default is 6379.
  • REDIS_PREFIX The prefix to be used for entire application. Change this and all entries are invalidated. Default is bibdk-api-1.
  • REDIS_ENABLED Default is true.

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