Error 404 Not Found — When Your S3 Object Disappears into the Void

When S3 returns a “404 Not Found,” it’s rarely lying — but it’s often misunderstood.

Problem

You upload an object to your S3 bucket, see it in the console, and confirm it’s there. Then, moments later, your app throws this message:

Error: 404 Not Found

You try again through the CLI or a presigned URL and still — nothing.

Your object has seemingly vanished into the digital ether.

Clarifying the Issue

A “404 Not Found” response from Amazon S3 doesn’t always mean the file is missing.
It simply means S3 couldn’t locate the exact object version that matches your request — and that can happen in several subtle ways.
Often the culprit is regional confusion: you’re querying us-east-1 when the bucket actually lives in us-west-2.
Other times, it’s a key mismatch: S3 is case-sensitive, so `Image.png` and `image.png` are two different keys.
Permissions are another silent offender; your IAM policy or ACL might restrict visibility even though the object exists.
In versioned buckets, the “latest” version may have been deleted, leaving no visible copy at all.
And finally, a small but real factor — DNS or CloudFront propagation delay — can make a newly uploaded file temporarily unreachable.
In short, a 404 in S3 is usually a visibility problem, not a deletion.

Why It Matters

This error can quietly break production systems.
When your CI/CD pipeline uploads new artifacts or your web app relies on S3-hosted assets, a 404 can trigger missing resources, failed deployments, and a loss of confidence in your automation.
Imagine a new build artifact is uploaded, but your deployment script can’t find it. Or a critical product image disappears from a customer’s shopping cart. This error can lead to a silent, cascading failure where everything appears normal to you, yet clients can’t access the file.
Understanding this gap between existence and visibility is essential to maintaining reliability.

Key Terms

Object Key: The full path and filename identifying an S3 object.
Region: The AWS data-center location where your bucket resides.
ACL (Access Control List): A legacy permission mechanism still influencing object visibility.
Bucket Policy: JSON rules defining who can access your bucket and under what conditions.
Presigned URL: A temporary, credential-based URL that grants time-limited access.
Propagation: The delay while DNS, CloudFront, or replication catches up with a change.

Steps at a Glance

Verify the region.
Check the object key for exact casing and path.
Validate permissions (ACLs and policies).
Confirm the credentials or account used.
Regenerate presigned URLs if keys rotated.
Allow for cache and DNS propagation.

Detailed Steps

Step 1 — Verify the Region
Run:

aws s3api head-object --bucket your-bucket-name --key path/to/object --region us-west-2

If you receive a 404, double-check the region:

aws s3api get-bucket-location --bucket your-bucket-name

Always specify the --region flag to override your CLI’s default configuration.

This ensures you’re querying the correct AWS region, even if your environment is preconfigured.

Step 2 — Double-Check the Object Key
S3 treats keys as case-sensitive text. A single letter difference is enough to break retrieval.

You can confirm the exact key name by listing recursively:

aws s3 ls s3://your-bucket-name/ --recursive | grep 'image'

Example output:

2023-10-25 15:30:00        12345 path/to/Image.png

Be sure the key and prefix match your code exactly — no hidden folder slashes or capitalization drift.

Step 3 — Validate Permissions
Visibility depends on both bucket policy and IAM permissions.

Inspect the policy:

aws s3api get-bucket-policy --bucket your-bucket-name

Ensure that "s3:GetObject" is allowed for your caller.

Then verify the ACL:

aws s3api get-object-acl --bucket your-bucket-name --key path/to/object

If either layer denies access, S3 returns a 404 instead of a 403, masking the root cause.

Step 4 — Confirm Credentials and Account Alignment
Presigned URLs or Lambda functions may belong to a different AWS account than the bucket owner.

Run:

aws sts get-caller-identity

and confirm that the Account ID matches the one expected in the bucket policy.

Step 5 — Regenerate Presigned URLs
Presigned URLs are cryptographically tied to your credentials.
If keys rotate or roles change, those URLs immediately expire.

Regenerate them:

aws s3 presign s3://your-bucket-name/path/to/object --expires-in 3600

Step 6 — Check Propagation and Caching
If you’re serving through CloudFront, create an invalidation:

aws cloudfront create-invalidation --distribution-id YOUR_DIST_ID --paths "/*"

For DNS-backed endpoints, allow a short window for propagation.
S3 is strongly consistent, but caches can lag briefly after updates.

ProTip #1 — Trace 404 Errors with CloudTrail Logs
You can confirm whether S3 ever received the GetObject call by searching CloudTrail for the event name GetObject.

If the log shows no matching entry, your request never reached the bucket — a clear sign of region mismatch or DNS routing error.

If the log shows the request but with an Access Denied result, the 404 was actually a masked permission failure.

CloudTrail gives you the forensics to separate missing from invisible.

ProTip #2 — The CLI Pocket Reference for 404 Troubleshooting
For quick command-line triage, these five commands cover nearly every root cause of a “Not Found” response:

# Check bucket region
aws s3api get-bucket-location --bucket your-bucket-name

# Verify object existence
aws s3api head-object --bucket your-bucket-name --key path/to/object --region us-west-2

# Inspect permissions
aws s3api get-bucket-policy --bucket your-bucket-name

# Confirm credentials
aws sts get-caller-identity

# Regenerate presigned URL (valid for 1 hour)
aws s3 presign s3://your-bucket-name/path/to/object --expires-in 3600

Keep this sequence handy — it’s the 80/20 shortcut that resolves most S3 404s in minutes.

Conclusion

When S3 returns a “404 Not Found,” it’s rarely lying — but it’s often misunderstood.
The object isn’t gone; it’s simply beyond the scope of your current view, perhaps in another region, under a different key, or behind a permission barrier.
Precision, patience, and a systematic check of each layer will save hours of guessing.
Every 404 is a lesson in cloud visibility: what you can’t see still exists, just waiting for the right credentials and coordinates.
Aaron Rose is a software engineer and technology writer at tech-reader.blog and the author of Think Like a Genius.

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