When Uploads Break: Solving S3 Failures on a New Mac

When Uploads Break: Solving S3 Failures on a New Mac

You upgrade your laptop expecting a smoother ride—but then S3 uploads stop working. That’s exactly what happened after moving from a MacBook Air M2 to the M4. Files under 200 KB uploaded just fine. Anything larger triggered a vague “Networking Error” in the AWS Console. The CLI? SSL timeouts.

Same network. Same credentials. Same bucket. Everything worked on the old laptop.

When the Cloud Isn’t the Problem

This kind of failure is subtle. No access denied, no obvious misconfig. Just broken uploads. And that’s the worst kind—where everything should work, and nothing does.

When this happens after a hardware or OS upgrade, you’re not really debugging AWS. You’re debugging your local stack. Updated system libraries, changed TLS defaults, stricter security layers—they can quietly break your connection to cloud services you rely on daily.

Fix It with the CLI

Start by checking your AWS CLI version:

 

bash

aws --version

If it's outdated or misbehaving, upgrade:

bash

brew update && brew upgrade awscli

Then try the upload again:

bash

aws s3 cp largefile.zip s3://your-bucket-name/

If it fails, get detailed output:

bash

aws s3 cp largefile.zip s3://your-bucket-name/ --debug

Look for SSL handshake issues or timeouts.

If multipart uploads are tripping up the CLI, adjust the thresholds:

bash

aws configure set default.s3.multipart_threshold 50MB 
aws configure set default.s3.multipart_chunksize 10MB

This tells the CLI how to break up large files for transfer. These settings live in ~/.aws/config.

Still stuck? Try helping AWS anticipate the size:

bash

aws s3 cp largefile.zip 
    s3://your-bucket-name/ 
    --expected-size 500000000

And if you're suspicious of your ISP or network path, connect through a VPN and test again.

The Quiet Breakage We Never See Coming

When things suddenly break on a new laptop, it’s easy to blame AWS. But the cause is usually local—subtle changes in security policies, network behavior, or how your system handles multipart uploads.

It’s not a permissions issue. It’s a handshake problem. And you fix it by meeting the cloud where it is—one CLI setting at a time.

Need AWS Expertise?

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