Same-host vs CDN

Default same-host URLs vs public_base_url rewrite modes.

Default: same-host

With public_base_url empty (default):

1. WordPress keeps advertising /wp-content/uploads/... on your site domain.
2. If the file exists locally, PHP/nginx serves it as usual.
3. If missing, the plugin streams the object from S3 (response header X-WP-To-S3: 1).
4. Optional: WP_TO_S3_REDIRECT_MISSING for a 302 to a public or presigned S3 URL.
5. You can put Cloudflare (or similar) in front of the site to cache same-host media.

No forced rewrite to provider hostnames.

Optional: public_base_url

When WP_TO_S3_PUBLIC_BASE_URL (or Media → WP to S3 → Public base URL) is set:

• wp_get_attachment_url, image src, and srcset rewrite to that base + the same relative path.
• _wp_attached_file metadata is not changed.
• Browser requests typically hit the CDN/bucket directly; the PHP stream path is unused for those URLs.
• Same-host paths still work if something requests them and the local file is missing (Serve still registered).

Example:

Uploads base:  https://example.com/wp-content/uploads
public_base:   https://cdn.example.com/media
Attachment:    https://cdn.example.com/media/2020/03/foo.jpg
Object key:    2020/03/foo.jpg  (plus optional prefix)

Historic post content

Old post HTML may still contain absolute https://example.com/wp-content/uploads/... links.

• Default: do nothing (same-host URLs remain correct forever if you stay on same-host mode).
• When using CDN: enable Content rewrite toggle in Settings, then use Tools → Dry-run then Apply to rewrite post/page content only.
• Content rewrite never runs automatically.

Choosing a mode