HTTP 404 Not Found in AWS S3
Amazon S3 — object storage, often fronting a static site or CDN.
What triggers it in AWS S3
Key doesn't exist, or the caller has `s3:ListBucket` denied (S3 returns 404 to hide existence).
How to fix it on AWS S3
Confirm the object key exactly (case-sensitive), then grant `s3:ListBucket` on the parent prefix if you want a true 404 vs 403 signal.
Where you'll see it
S3 access logs, CloudFront distribution logs, or the browser response headers (`x-amz-request-id`).
Monitor 404 responses continuously
Lemwatch checks your AWS S3 endpoints as often as every 5 minutes and alerts the moment a 404 pattern appears — with the full response headers and body captured, so you can debug without waiting for the next customer report.
Same error on other platforms
404 Not Found in AWS S3 — FAQs
Key doesn't exist, or the caller has `s3:ListBucket` denied (S3 returns 404 to hide existence).
Confirm the object key exactly (case-sensitive), then grant `s3:ListBucket` on the parent prefix if you want a true 404 vs 403 signal.
404 on AWS S3 is a client-side condition, so it will keep returning until the request or configuration is corrected. Retrying the same request without changes will produce the same 404 response.
High SEO impact. 404s waste crawl budget (Googlebot stops crawling broken paths but keeps re-checking them), drop the link equity of inbound backlinks (a backlink to a 404 page gives you nothing), and erode user trust. Google does not penalise sites for having some 404s — it expects them — but it does penalise sites with a high proportion of broken internal links or large numbers of previously-indexed pages now returning 404 without redirects. Sites that migrate without redirects routinely lose 40-80% of organic traffic. On AWS S3 specifically, Googlebot sees the same 404 your users see, so unresolved errors get reflected in Search Console's Page indexing report within days.
Set up an HTTP monitor that pings your key AWS S3 endpoints from multiple regions every 1–5 minutes and alerts on any non-2xx response. Lemwatch does this out of the box — including capturing the full response headers and body when a 404 hits, so you can debug without waiting for the next user report.
Both are client error responses, but they mean different things: 404 Not Found indicates the requested resource could not be found on the server — the page may have been deleted, moved, or the url was typed incorrectly., while 301 is a distinct condition with its own root cause. On AWS S3, the fix path and the log signature are different — check the exact status code your AWS S3 logs return before applying a fix.