adding_a_new_rest_microservice.md

Adding a new Microservice to Metaphysics

Ideal place we want to be: You don't need to do this because you're using GraphQL and Stitching your schema. However, if you need to add in a service manually follow this guide.

Let's pretend we're mapping an API called Three Body which uses Gravity to generate a short-term JWT for your app.

1. Add your ENV Vars:

   THREE_BODY_APP_ID="xxx_gravity_app_id_xxx"
   THREE_BODY_API_BASE="https://threebody-staging.artsy.net/api"
   THREE_BODY_GEMINI_TEMPLATE="three-body-submission"

   These will need to be added to : Your .env, .env.example, .env.test and the live environments, as well as included in ./src/config.js

2. Create an API: lib/apis/threeBody.js

   This is function which is used for any API call to your service. Depending on what you want to map, it should probably look like this if you have mutations:

   import { assign } from "lodash"
   import fetch from "./fetch"
   import config from "config"
   
   const { THREE_BODY_API_BASE } = config
   
   export default (path, accessToken, fetchOptions = {}) => {
     const headers = {}
     if (accessToken)
       assign(headers, { Authorization: `Bearer ${accessToken}` })
     return fetch(
       `${THREE_BODY_API_BASE}/${path}`,
       assign({}, fetchOptions, { headers })
     )
   }

   Or this if you're only reading:

   import fetch from "./fetch"
   const { THREE_BODY_API_BASE } = config
   
   export default path => fetch(`${THREE_BODY_API_BASE}/${path}`)

3. Create an API loader factory: lib/loaders/api/index.js

   This links the API calls to a loader, which ensures that all API requests to the same service are cached correctly. It should look something like:

   import positron from "lib/apis/positron"
   + import threeBody from "lib/apis/threeBody"
   
   ...
   
   + export const threeBodyLoaderWithAuthenticationFactory = apiLoaderWithAuthenticationFactory(threeBody)

4. Create a loader for your service: lib/loaders/loaders_with_authentication/threeBody.js

   Roughly, this looks something like:

   import {
     gravityLoaderWithAuthenticationFactory,
     threeBodyLoaderWithAuthenticationFactory,
   } from "../api"
   
   const { THREE_BODY_APP_ID } = config
   
   export default accessToken => {
     let threeBodyTokenLoader
     const gravityAccessTokenLoader = () => Promise.resolve(accessToken)
     const threeBodyAccessTokenLoader = () =>
       threeBodyTokenLoader().then(data => data.token)
   
     const gravityLoader = gravityLoaderWithAuthenticationFactory(
       gravityAccessTokenLoader
     )
     const threeBodyLoader = threeBodyLoaderWithAuthenticationFactory(
       threeBodyAccessTokenLoader
     )
   
     // This generates a token with a lifetime of 1 minute, which should be plenty of time to fulfill a full query.
     threeBodyTokenLoader = gravityLoader(
       "me/token",
       { client_application_id: THREE_BODY_APP_ID },
       { method: "POST" }
     )
   
     return {
       groupResultsLoader: threeBodyLoader(id => `/group/${id}`),
     }
   }

   Each of which corresponds to one API call: [THREE_BODY_API_BASE]/group/[id]. You would add more API loaders at the to the returned object as you add more routes to metaphysics.

5. Next you need to expose those loaders to the rootValue so you can access them in the resolvers, you can do that by editing /lib/loaders/loaders_with_authentication/index.js to add the following:

   import convectionLoaders from "./convection"
   + import threeBodyLoaders from "./threeBody"
   import impulseLoaders from "./impulse"
   
   ...convectionLoaders(accessToken),
   + ...threeBodyLoaders(accessToken),
   ...impulseLoaders(accessToken, userID),

6. If you have variables that clients might need to know that can differ between staging/production systems, you can extend the services object to include these variables so that each client does not need to hardcode the variables.

   Add an object that resolves to a process ENV var. Anything you expose will be available to the public, so don't put secrets in here.

   // @ts-check
   import { GraphQLNonNull, GraphQLString, GraphQLObjectType } from "graphql"
   
   const ThreeBodySchema = new GraphQLObjectType({
     name: "ThreeBody",
     fields: () => ({
       threeBodyTemplateKey: {
         type: new GraphQLNonNull(GraphQLString),
       },
     }),
   })
   
   const ThreeBody = {
     type: ThreeBodySchema,
     description: "The schema for Three Body's ENV settings",
     args: {},
     resolve: () => ({
       threeBodyTemplateKey: config.THREE_BODY_GEMINI_TEMPLATE,
     }),
   }
   
   export default ThreeBody

   Then add a reference to this in /schema/v1/services/index.js.

From here you need to handle the usual work of adding mutations for writing data, and updating the schema for reading data. Good luck!

If you want to see a PR where this comes together, check out #726.