Apollo Server

Apollo Server is an open source GraphQL server. It enables the use of the GraphQL query language to make requests against the server.

Internally it uses concepts such as data sources, resolvers and schemas.

The schemas are written in GraphQL and show what the server provides and can accept in terms of requests.

Resolvers help to tie requests together to connect one graph entity to another.

Data sources are where the server gets its data from which could be other APIs, databases, and various combinations inbetween.