DNS Lookup Error when uploading to localhost (local S3 server)

Question

In a docker container, the scality/s3server-image is running. I am connecting to it with NodeJS using the @aws-sdk/client-s3 API.

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The S3Client setup looks like this:

const s3Client = new S3Client({
  region: undefined, // See comment below
  endpoint: 'http://127.0.0.1:8000',
  credentials: {
    accessKeyId: 'accessKey1',
    secretAccessKey: 'verySecretKey1',
  },
})

Region undefined: this answer to a similar question mentions to leave the region out, but, accessing the region with await s3Client.config.region() still displays eu-central-1, which was the value I passed to the constructor in a previous version. Although I changed it to undefined, it does still take the old configuration. Could that be connected to the issue?

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It was possible to successfully create a bucket (test) and it could be listed by running a ListBucketsCommand (await s3Client.send(new ListBucketsCommand({}))).

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However, as mentionned in the title, uploading content or streams to the Bucket with

bucketParams = {
  Bucket: 'test',
  Key: 'test.txt',
  Body: 'Test Content',
}
await s3Client.send(new PutObjectCommand(bucketParams))

does not work, instead I am getting a DNS resolution error (which seems odd, since I manually typed the IP-address, not localhost.

Anyway, here the error message:

Error: getaddrinfo EAI_AGAIN test.127.0.0.1
    at GetAddrInfoReqWrap.onlookup [as oncomplete] (node:dns:72:26) {
  errno: -3001,
  code: 'EAI_AGAIN',
  syscall: 'getaddrinfo',
  hostname: 'test.127.0.0.1',
  '$metadata': { attempts: 1, totalRetryDelay: 0 }
}

---

Do you have any idea on

• why the region is still configured and/or
• why the DNS lookup happens / and then fails, but only when uploading, not when retrieving metadata about the Buckets / creating the Buckets?