Connection Error

Help
,
1 
const { ApolloClient, InMemoryCache, HttpLink } = require('@apollo/client');
const fetch = require('cross-fetch');

const headers = {
  "Content-Type": "application/json",
  "Hasura-Client-Name": "hasura-console",
  "x-hasura-admin-secret": "myadminsecretkey",
};

const client = new ApolloClient({
  link: new HttpLink({
    uri: "http://localhost:8081/v1/graphql",
    headers,
    fetch
  }),
  cache: new InMemoryCache()
});

module.exports = client;

Using this to initialise my client is throwing me error:

leave-tracker-functions-1       |   networkError: FetchError: request to http://localhost:8081/v1/graphql failed, reason: connect ECONNREFUSED 127.0.0.1:8081
leave-tracker-functions-1       |       at ClientRequest.<anonymous> (/app/node_modules/cross-fetch/node_modules/node-fetch/lib/index.js:1491:11)
leave-tracker-functions-1       |       at ClientRequest.emit (node:events:513:28)
leave-tracker-functions-1       |       at Socket.socketErrorListener (node:_http_client:494:9)
leave-tracker-functions-1       |       at Socket.emit (node:events:513:28)
leave-tracker-functions-1       |       at emitErrorNT (node:internal/streams/destroy:157:8)
leave-tracker-functions-1       |       at emitErrorCloseNT (node:internal/streams/destroy:122:3)
leave-tracker-functions-1       |       at processTicksAndRejections (node:internal/process/task_queues:83:21) {
leave-tracker-functions-1       |     type: 'system',
leave-tracker-functions-1       |     errno: 'ECONNREFUSED',
leave-tracker-functions-1       |     code: 'ECONNREFUSED'
leave-tracker-functions-1       |   },
leave-tracker-functions-1       |   extraInfo: undefined
leave-tracker-functions-1       | }

I tried using host.docker.internal, it didn’t work.
What worked for me is
uri: 'http://leave-tracker-graphql-engine-1:8080/v1/graphql',

I’m trying to understand why this works.

Config for my hasura docker container:

graphql-engine:
    image: hasura/graphql-engine:v2.16.1
    ports:
      - "8081:8080"