GraphQL - A query language to empower your API Consumers (DDD Melbourne 2017)

The shift to microservices, cloud native and rich web apps have made it challenging to deliver compelling API experiences. REST, as specified in Roy Fielding’s seminal dissertation, has become the architectural pattern of choice for APIs and when applied correctly allows for clients and servers to evolve in a loosely coupled manner. There are areas however where REST can deliver less than ideal client experiences. Often many HTTP requests are required to render a single view.
While this may be a minor concern for a web app running on a WAN with low latency and high bandwidth, it can yield poor client experiences for mobile clients in particular. GraphQL is Facebook’s response to this challenge and it is quickly proving itself as an exciting alternative to RESTful APIs for a wide range of contexts. GraphQL is a query language that provides a clean and simple syntax for consumers to interrogate your APIs. These queries are strongly types, hierarchical and enable clients to retrieve only the data they need.

In this session, we will take a hands-on look at GraphQL and see how it can be used to build APIs that are a joy to use.

Transcript

1. @robdcrowley | robdcrowley GraphQL A query language to empower your API consumers
2. Goals for the session -Explore the motivation behind GraphQL and the category of problems it helps to solve. -Take a tour of GraphQL’s features and see it in action. -Investigate how to effectively leverage GraphQL in your delivery process. -Most of all sufficiently motivate you to continue to learn GraphQL after leaving this conference.
3. The shift to microservices, cloud native and rich web apps have made it challenging to deliver compelling API experiences
5. Image Service Cross Sell Service Product Service Product Service Product Service Review Service Price Service Inventory Service Promotions Service Other Sellers Service Price Service Image Service Inventory Service Order Service Image Service Price Service
6. Cross Sell Component Header Component Product Image Component Product Review Component Product Price Component Product Inventory Component Product Purchase Component Alternate Sellers Component Product Details Component Offers Component Product Header Component
7. How can we efficiently deliver the data to the client?
8. A naïve approach Microservice Microservice Microservice Microservice Component Potentially high latency connection Component Component Component
9. Leveraging an API Gateway to reduce latency Microservice Microservice Microservice Microservice API Gateway Wait, we support more than one customer experience channel. How to handle these? Component Component Component Component
10. Introducing Backends for Frontends (BFFs) Microservice Microservice Microservice Microservice Mobile BFF Desktop BFF Wearables BFF What about the different data requirements between versions? V4, V5… On page reload V1, V2…
11. Retrieve exactly the data you require in a single round trip to the server
12. GraphQL as the translation layer Microservice Relational DB Graph DB Web Service GraphQL API Retrieve exactly the data every version of each channel experience requires in one round trip. optimised { data }
13. Source code available at https://github.com/robcrowley/graphql-demo
14. Our Example Domain Album Artist Label User Album Review compose submit favourite released on refers to 1 * * 1 1 * * 1 1 * artistId: int name: string albumId: int title: string labelId: int name: string founded: int userId: int name: string reviewId: int albumId: int review: string rating: int
15. Demo time: Just show me how it works already
16. Hey, just what are you trying to pull here!? Couldn’t we already do this with REST? Absolutely, but GraphQL makes it trivial and ensures a consistent interface.
17. GraphQL Core Concepts
18. Type System Execution Engine Anatomy of GraphQL Query Language
19. “Reliability problems largely occur at module boundaries, and most result from inconsistencies in both sides expectations” - Bertrand Meyer
20. type Artist { id: ID! name: String! aliases: [String] albums: [Album] }
21. let queryArtist = (_, {id}, {dao}) => { // arbitrary code to retrieve artist return dao.getArtist(id); } let artistName = artist => { return artist.name; }
22. root query { artist(id: “5”) { name albums { title label { name } } } } Label Producer Album User Artist Review
23. root query { artist(id: “5”) { name albums { } } } Label Producer Album User Artist Review
24. root Label Producer Album User Artist Review query { artist(id: “5”) { name albums { title label { } } } }
25. root Label Producer Album User Artist Review query { artist(id: “5”) { name albums { title label { name } } } }
26. Capabilities exposed as schema Requirements expressed as query GraphQL focusses on accessing data exposed by the graph This is a fundamental difference to REST which is concerned with modelling resources and state transitions. Clients Single /graphql endpoint *
27. GraphQL Operations -Query -> Read ( 1 : 1 ) -Mutation -> Write ( 1 : 1 ) -Subscription -> Observe Event ( 1 : 0..* )
28. -The second killer feature of GraphQL -Enables ‘reflection’ type queries on fields, types and schema -Extremely powerful for tooling support - Autocomplete (as seen in Graphiql) - Code generation - Documentation Introspection
29. Efficiency -Avoid overfetching and underfetching (particularly across the slow portion of the network to the client). -Reduced data handling complexity in the client. -Simpler extension model for backend API developers.
30. GraphQL is not tied to JavaScript. Server implementations exist for many languages. http://graphql.org/code
31. GraphQL is protocol agnostic. So long as the protocol supports exchanging character data you’re set.
32. GraphQL is not about binary data streams
33. “Every time time you change a version identifier, you’re potentially orphaning clients who ‘speak’ that language.” - Mark Nottingham
34. In place of versioning prefer an extension model to enable graceful evolution of the API contract
35. The @deprecated directive provides an elegant mechanism to facilitate this in GraphQL
36. GraphQL is not a shortcut to great API design. Solid modelling skills are still table stakes. (sorry, not sorry)
37. Think in Graphs* Avoid creating fields that should be types <zen> </zen>
38. Getting the most out of GraphQL
39. The schema solves one part of the API documentation challenge, it does not solve it completely
40. graphdoc + schema = professional static API documentation
41. Do not roll your own GraphQL client
42. Decide whether you will support Relay early https://facebook.github.io/relay
43. Naming is difficult and as such is a problem suited to API governance
44. is / can / has prefix for Boolean fields plural nouns for collections
45. Strive for field and type names that mirror the language of the business domain
46. “There are only two hard things in Computer Science: cache invalidation and naming things.” - Phil Karlton
47. GraphQL requires a different approach to caching
48. Caching Approaches for RESTful APIs Client Side Caching Server Side Caching HTTP offers rich caching functionality via caching headers: Cache-Control, ETag, Expires, Pragma & Vary.
49. Caching Approaches for RESTful APIs Client Side Caching Server Side Caching Intermediate Caching Proxy HTTP offers rich caching functionality via caching headers: Cache-Control, ETag, Expires, Pragma & Vary.
50. Caching Approaches for GraphQL APIs Client Side Caching Server Side Caching Intermediate Caching Proxy GraphQL does not play nice with the rest of the web, as it treats HTTP as a dump pipe. As such we need to rely on server and client caching.
51. Server Caching - Utilise a dedicated cache layer to minimize traffic downstream. - DataLoader implementations assist with per request batching and caching.
52. Client Caching - GraphQL clients such as Apollo or Relay help massively in this regard. - Hierarchical responses are flattened to create normalized caches where each record is stored exactly once. - Clients can leverage this cache to generate network efficient queries. query: { album (id: “1”): { name: “Endtroducing…" artist: { name: “DJ Shadow" } } } Map { 1: Map { name: “Endtroducing…”, author: Link(2), }, 2: Map { name: ‘DJ Shadow' }, }; Hierarchical Normalized
53. Inter API Communication - Inter API calls are easily supported in REST APIs based of the media type semantics. - In fact, Hypermedia is the under- pinning architectural style of the web. GET /artistsapi/artist/1 HTTP/1.1 ContentType: application/vnd.hal+json { “_links”: { “events” : { “href”: “/eventsapi/performers/8”, “type” : “application/vnd.siren+json” } /* … other fields … */ } Events API Artists API
54. Inter API Communication - Inter API calls are easily supported in REST APIs based of the media type semantics. - In fact, Hypermedia is the under- pinning architectural style of the web. GET /eventsapi/events/8 HTTP/1.1 ContentType: application/vnd.siren+json { "class": [ “event" ], "properties": { “startDate": “2017-09-18T15:00:00+10:00”, “endDate: “2017-08-18T16:00:00+10:00”, “availableTicketCount": 42 }, /* … other fields … */ } Events API Artists API
55. { “data”: { “artist” : { “events”: [ { “url”: “/eventsapi/performers/8” } ] } } } Inter API Communication - There is no easy way to federate calls across GraphQL schemas. - Ideally model these as additional nodes and edges in the same GraphQL schema. - Failing this we must defer to ‘out of band’ sources such as API documentation. POST /graphql HTTP/1.1 { artist { events { url } } } Events API GraphQL API
56. { “data”: { “artist” : { “events”: [ { “url”: “/eventsapi/performers/8” } ] } } } Inter API Communication - There is no easy way to federate calls across GraphQL schemas. - Ideally model these as additional nodes and edges in the same GraphQL schema. - Failing this we must defer to ‘out of band’ sources such as API documentation. POST /graphql HTTP/1.1 { artist { events { url } } } Events API GraphQL API ?
57. Authentication & Authorization
58. GraphQL REST RPC Business Logic Authentication Authentication Authorization HTTP TCP based protocol
59. As a User, I want to be the only one permitted to see my personal details So that my right to privacy is respected
62. This approach works well for 1st party systems. What about 3rd party systems with delegated access?
63. Authentication Authentication HTTP TCP based protocol REST RPC Coarse Grained Authorization GraphQL Business Logic Authorization
66. Image by toffehoff via https://www.flickr.com/photos/toffehoff/244870161/ So far we have been pulling data what if we could we enable the pushing of data
67. As a User, I want to be notified when my favourite artists release albums So that I can keep to up to date with the music that I love
68. Real Time APIs -Pull -Polling -Push -Live Queries (standard query with infinitely fast polling) -Subscriptions (event based)
69. Subscriptions RFC has been raised facebook/graphql#267
70. Event Based Subscriptions -Concept: Server pushes message to client when ‘something’ occurs -Read only -Expressed using GraphQL syntax -Not a replacement for GraphQL queries!
71. Client Request / Response GraphQL Business Domain
72. Subscriptions Client Request / Response GraphQL Events Bi-directional Transport Business Domain
73. Subscriptions Client Request / Response GraphQL Events Bi-directional Transport Business Domain Subscription Event
74. Example subscription workflow / use case User Admin GraphQL Server Connect to WS endpoint (ws://api.example.com/subscriptions)
75. Example subscription workflow / use case Subscribe to advertised event (http://api.example.com/graphql) subscription onAlbumAdded { albumAdded(userId: “1”) { album { title } artist { name } } } User Admin GraphQL Server Web socket connection open and waiting for published events
76. Example subscription workflow / use case User Admin mutation addAlbum { addAlbum(album: {title: "Cold Water Music", artistId: 1, labelId: 1 }) { artist { id name } } } Admin user adds new album using addAlbum mutation GraphQL Server Web socket connection open and waiting for published events
77. Album added event document pushed to client Example subscription workflow / use case User Admin { albumAdded: { album: { title: “Cold Water Music” } artist: { name: “Aim” } } } GraphQL Server
78. Low friction development of GraphQL APIs
79. GraphQL Dev Workflow - Front end and back end teams agree on schema. - UI is developed using mocked data based on schema - API is built out with any changes being communicated to front end team - Integrate front and back ends - Ship - Repeat Schema App Api Product
80. GraphQL Dev Workflow - Front end and back end teams agree on schema. - UI is developed using mocked data based on schema - API is built out with any changes being communicated to front end team - Integrate front and back ends - Ship - Repeat Schema App Api Product
81. GraphQL Dev Workflow - Front end and back end teams agree on schema. - UI is developed using mocked data based on schema - API is built out with any changes being communicated to front end team - Integrate front and back ends - Ship - Repeat Schema App Api Product
82. GraphQL Dev Workflow - Front end and back end teams agree on schema. - UI is developed using mocked data based on schema - API is built out with any changes being communicated to front end team - Integrate front and back ends - Ship - Repeat Schema App Api Product
83. { real { data } fake { data } } { real { data } } { real { data: “resolved” } } { real { data: “resolved” } fake { data: “stubbed” } } IDL application/graphql application/json GraphQL Faker facilitates low friction experimentation when modelling schema. It’s quicker to change IDL than the API.
84. GraphQL Faker Demo https://github.com/APIs-guru/graphql-faker
85. Query execution telemetry is vital for identifying performance bottlenecks
86. Build support for a phased release approach for API changes
87. Thank you!
88. Resources - Official Docs: http://graphql.org - Specification: https://github.com/facebook/graphql - Reference: https://github.com/graphql/graphql-js - Community: http://graphql.org/community - Awesome List: https://github.com/chentsulin/awesome-graphql - Humble Additions - Code: https://github.com/robcrowley/graphql-demo - Slides: https://bit.ly/ddd-melbourne-rc-graphql