Sample of merge Schemas using stitching

link-service-with-category.js

export default `
  extend type Service {
    category: Category
  }
`;

merge-schemas.js

import graphqlTools from 'graphql-tools';
import serverOneFetcher from './server-fetcher-one';
import serverTwoFetcher from './server-fetcher-two';
import SchemaBuilder from './schema-builder';
import serviceStitching from './stitching-service';
import linkServiceCategorySchema from './link-service-with-category';

const schemas = [];
const fetchers = {
  serverOne: serverOneFetcher,
  serverTwo: serverTwoFetcher,
};

export default async () => {
  try {
    await Promise.all(
      Object.values(fetchers).map(async (fetcher) => {
        schemas.push(await SchemaBuilder(fetcher));
      }),
    );

    schemas.push(linkServiceCategorySchema);

    return graphqlTools.mergeSchemas({
      schemas,
      resolvers: mergeInfo => serviceStitching(mergeInfo),
    });
  } catch (error) {
    console.log('error:', error);
    return error;
  }
};

schema-builder.js

import graphqlTools from 'graphql-tools';

const schemaBuilder = async fetcher => graphqlTools.makeRemoteExecutableSchema({
  schema: await graphqlTools.introspectSchema(fetcher),
  fetcher,
});

export default schemaBuilder;

server-fetcher-one.js

import apolloFetch from 'apollo-fetch';
import config from './config';

const serverFetcher = apolloFetch.createApolloFetch({
  uri: config.serverGraphEndpoint,
});

export default serverFetcher;

server-fetcher-two.js

import apolloFetch from 'apollo-fetch';
import config from './config';

const serverFetcher = apolloFetch.createApolloFetch({
  uri: config.serverTwoGraphEndpoint,
});

serverFetcher.use(({ options }, next) => {
  if (!options.headers) {
    Object.assign(options, {
      headers: {
        'api-key': config.serverTwoGraphApiKey,
      },
    });
  }

  next();
});

export default serverFetcher;

stitching-service.js

const serviceStitching = function (mergeInfo) {
  return {
    Service: {
      category: {
        fragment: 'fragment CategoryTypeFragment on Category { slug }',
        resolve(parent, args, context, info) {
          return mergeInfo.delegate(
            'query',
            'category',
            { slug: parent.categorySlug },
            context,
            info,
          );
        },
      },
    },
  };
};

export default serviceStitching;