Image Layer - CI/CD Glossary Definition
An image layer is one immutable, content-addressed filesystem change in a container image. Each instruction in a Dockerfile that alters the filesystem (COPY, RUN, ADD) produces a layer, and layers are stacked to form the final root filesystem.
Why layers matter for CI speed
Layers are cached and shared by digest. If an early layer (for example dependency install) is unchanged, the registry and the build host reuse it instead of rebuilding, which is the main reason ordering a Dockerfile from least-changing to most-changing speeds up CI.
Inspecting layers
Terminal
docker history myimage:latest
docker buildx imagetools inspect myimage:latestRelated guides
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