Answer
Docker uses union FS (Overlay2) to merge read-only layers with a writable layer. Modifications occur only in the upper layer to preserve base layers.
Quick Answer
Union filesystems stack layers into one virtual filesystem view. OverlayFS has a lower dir (read-only image layers merged) and upper dir (writable container layer). Reads check upper first, then lower. Writes go to upper — but first Docker copies the file from lower to upper (copy-on-write) so the lower layer stays unchanged.
S
SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
Want to bookmark, take notes, or join discussions?
Sign in to access all features and personalize your learning experience.
Source: SugharaIQ