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World Congress 2026 Europe • Jul 9, 2026 • Session details

Docker build without Docker

Oliver Seitz

Deleting a file during a Docker build doesn't actually remove it from the archive. Uncover the true mechanics of container layers to master image optimization.

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#1 about 4 min

Anatomy of a Docker image and content addressing

How Docker images use tar archives, JSON metadata, and hashes to structure layers in a registry.

#2 about 5 min

Querying a container registry and extracting image layers

Downloading the Alpine image manifest and manually uncompressing its filesystem layer using curl and tar.

#3 about 8 min

Constructing a new Docker layer from scratch

Manually creating a new compressed layer, recomputing hashes, and updating JSON configuration to extend an Nginx image.

#4 about 4 min

Managing deleted files and container layer cache bloat

Why deleting large files in a subsequent layer does not reclaim space due to whiteout file markers.

#5 about 6 min

Understanding Linux OverlayFS mechanics for container filesystems

Demystifying copy-on-write functionality using lower, upper, and merged directories alongside character devices.

#6 about 3 min

Translating Dockerfile instructions into OverlayFS layer snapshots

How the build daemon executes instructions by mutating the upper directory and zipping intermediate states.

#7 about 2 min

Summary and access to demonless build examples

Repository access for the manual image construction scripts and final thoughts on container internals.

Matching moments

4:41 min

Docker official best practices for container image architecture

Madhu Akula · LIVE

3:52 min

Managing ephemeral system layers in Docker containers

Rob Richardson · LIVE

3:16 min

Demystifying the mechanics behind container execution routines

Oliver Seitz Oliver Seitz · WWC 2024

4:15 min

Building and optimizing Docker images using Spring Boot layers

Aleksandr Kalikov · LIVE

6:15 min

Optimizing image builds using buildpacks and native images

Eva Panadero Eva Panadero +1 · WWC 2025

1:48 min

Optimizing container images using multi-step build processes

Adrian Kosmaczewski · LIVE

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