GraphQL Subscriptions

Introduction

Subscriptions is new functionality added in version 4.0 In simple terms subscriptions are a way to push data from the server to the clients that choose to listen to real-time messages from the server.

In Tyk subscriptions are using the WebSocket protocol.

Subscriptions schema

The Subscription type always defines the top-level fields that consumers can subscribe to. For example:

type Subscription {
  reviewCreated: Post
}

The reviewCreated field will be updated each time a new review is published. Publishing a new review means a Post is created on the backend and then pushed to the subscribing consumers.

Consumers can subscribe to the reviewCreated field by sending the following query to the server:

subscription Reviews {
  reviewCreated {
    author
    date
    review
  }
}

Enabling subscriptions

There is no need to enable subscriptions separately. They are supported alongside with GraphQL as a standard. The only requirement for subscriptions to work is to enable WebSockets in your Tyk Gateway configuration file.

How do subscriptions work in Tyk?

How we are ahead of everyone else

With Tyk, subscriptions are supported in federation as well. With version 4.0 you can federate GraphQL APIs that support subscriptions. Federating subscriptions means that events pushed to consumers can be enriched with information from other federated graphs.

Example of federation with subscriptions

We have 3 graphs that provide information about:

1. Users
2. Products
3. Reviews

Users

The Users service lists users who can add their reviews for different products:

extend type Query {
  me: User
}

type User @key(fields: "id") {
  id: ID!
  username: String!
}

Products

The Products service contains a list of products offered where Product price and stock is implemented as a subscription:

extend type Query {
  topProducts(first: Int = 5): [Product]
}

extend type Subscription {
  updatedPrice: Product!
  updateProductPrice(upc: String!): Product!
  stock: [Product!]
}

type Product @key(fields: "upc") {
  upc: String!
  name: String!
  price: Int!
  inStock: Int!
}

Reviews

The Reviews service holds all the opinions of users about certain products:

type Review {
  body: String!
  author: User! @provides(fields: "username")
  product: Product!
}

extend type User @key(fields: "id") {
  id: ID! @external
  username: String! @external
  reviews: [Review]
}

extend type Product @key(fields: "upc") {
  upc: String! @external
  reviews: [Review]
}

With Tyk’s implementation of subscriptions and federation it is possible to create a subscription that’s enriched with data from other federated graphs:

subscription {
updatedPrice{
  upc
  price
  name
  reviews {
    body
    author {
      username
      }
    }
  }
}

The price value will be pushed to consumers each time an item is sold, but the message will be enriched with data from the other subgraphs.