Error in docker-compose server is not defined

Question

I'm trying to run a very simple docker-compose.yml, but am getting a "ReferenceError: server is not defined" from index.js in the client container.

| /app/index.js:6
node-app_1      |     host: redis-server,
node-app_1      |                 ^

Here's the code:

index.js

const express = require('express');
const redis = require('redis');

const app = express();
const client = redis.createClient({
    host: redis-server,
    port: 6379
});

client.set('visits', 0);

app.get('/', (req,res) => {
    client.get('visits', (err,visits) => {
        res.send('Number of visit is: ' + visits);
        client.set('visits', parseInt(visits) + 1);
    })
})


app.listen(8081, () =>{
    console.log('Listening on port 8081');
})

docker-compose.yml

version: '3'
services:
  redis-server:
    image: 'redis'
  node-app:
    build: .
    ports:
      - '4001:8081'

Output of docker-compose up

redis-server_1  | 1:C 07 Nov 2020 16:52:30.899 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
redis-server_1  | 1:C 07 Nov 2020 16:52:30.900 # Redis version=6.0.9, bits=64, commit=00000000, modified=0, pid=1, just started
redis-server_1  | 1:C 07 Nov 2020 16:52:30.900 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf
redis-server_1  | 1:M 07 Nov 2020 16:52:30.901 * Running mode=standalone, port=6379.
redis-server_1  | 1:M 07 Nov 2020 16:52:30.902 # Server initialized
redis-server_1  | 1:M 07 Nov 2020 16:52:30.902 * Loading RDB produced by version 6.0.9
redis-server_1  | 1:M 07 Nov 2020 16:52:30.902 * RDB age 180 seconds
redis-server_1  | 1:M 07 Nov 2020 16:52:30.902 * RDB memory usage when created 0.77 Mb
redis-server_1  | 1:M 07 Nov 2020 16:52:30.903 * DB loaded from disk: 0.000 seconds
redis-server_1  | 1:M 07 Nov 2020 16:52:30.903 * Ready to accept connections
node-app_1      | 
node-app_1      | > start
node-app_1      | > node index.js
node-app_1      | 
node-app_1      | /app/index.js:6
node-app_1      |     host: redis-server,
node-app_1      |                 ^
node-app_1      | 
node-app_1      | ReferenceError: server is not defined
node-app_1      |     at Object.<anonymous> (/app/index.js:6:17)
node-app_1      |     at Module._compile (node:internal/modules/cjs/loader:1083:30)
node-app_1      |     at Object.Module._extensions..js (node:internal/modules/cjs/loader:1112:10)
node-app_1      |     at Module.load (node:internal/modules/cjs/loader:948:32)
node-app_1      |     at Function.Module._load (node:internal/modules/cjs/loader:789:14)
node-app_1      |     at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:72:12)
node-app_1      |     at node:internal/main/run_main_module:17:47
node-app_1      | npm ERR! code 1
node-app_1      | npm ERR! path /app
node-app_1      | npm ERR! command failed
node-app_1      | npm ERR! command sh -c node index.js
node-app_1      | 
node-app_1      | npm ERR! A complete log of this run can be found in:
node-app_1      | npm ERR!     /root/.npm/_logs/2020-11-07T16_52_31_324Z-debug.log
visits_node-app_1 exited with code 1

It doesn't find "redis-server", but according to the udemy course, it should find it because that's how it's identified in the composer.

What's the problem?

Answer 1

"redis-server" should be a string, and denoted by quotes:

const client = redis.createClient({
    host: 'redis-server',
    port: 6379
});