DOCKER IMAGES & LAYERS
A STEP-BY-STEP TUTORIAL
WHAT IS A DOCKER IMAGE
-> A Docker image is a read-only template used to create containers
-> It contains application code, runtime, libraries, and dependencies
-> Images are portable and can run consistently across environments
-> Built using a Dockerfile
WHAT ARE DOCKER LAYERS
-> Docker images are composed of multiple layers
-> Each layer represents a change or instruction
-> Layers are stacked to form the final image
-> All layers are immutable once created
HOW DOCKER IMAGES ARE BUILT
-> Docker reads the Dockerfile
-> Executes instructions one by one
-> Each instruction creates a new layer
-> Layers are combined into a final image
COMMON DOCKERFILE INSTRUCTIONS AND LAYERS
-> FROM
-> Defines the base image
-> Creates the first layer
-> RUN
-> Executes commands
-> Adds a new layer with changes
-> COPY / ADD
-> Transfers files into the image
-> Creates a new layer
-> ENV
-> Sets environment variables
-> Adds metadata layer
-> WORKDIR
-> Sets working directory
-> Affects subsequent instructions
-> CMD / ENTRYPOINT
-> Defines container startup behavior
-> Final layer configuration
LAYERED FILESYSTEM EXPLAINED
-> Each layer is read-only
-> Layers are stacked on top of each other
-> Docker merges them into a single unified filesystem
-> Containers add a writable layer on top
WRITABLE CONTAINER LAYER
-> Created when a container starts
-> Stores runtime changes
-> Includes logs, temporary files, and modifications
-> Removed when the container is deleted
DOCKER LAYER CACHING
-> Docker caches each layer during build
-> If nothing changes, cached layers are reused
-> Improves build performance
-> Changing one layer invalidates subsequent layers
LAYER REUSE AND SHARING
-> Multiple images can share common layers
-> Saves disk space and bandwidth
-> Faster image pulls and builds
-> Encourages reuse of base images
WHY DOCKER LAYERS MATTER
-> Efficient storage management
-> Faster build times
-> Faster deployment and scaling
-> Easy updates by rebuilding only changed layers
BEST PRACTICES FOR USING LAYERS
-> Use minimal base images
-> Combine RUN instructions where possible
-> Order instructions for optimal caching
-> Avoid unnecessary files in the image
-> Use multi-stage builds for cleaner images
FINAL SUMMARY
-> Docker images are built from layered instructions
-> Each layer is immutable and reusable
-> Containers run on top of these layers with a writable layer
-> Efficient layering improves speed, storage, and scalability
LEARN DOCKER IN DEPTH
-> Grab the Docker Mastery eBook
-> https://t.co/sC9bTrAJWt
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@FatimaNdiathie@GothamCitizen11 Montrez-nous plutôt la communication officielle de la CAF. C'est trop facile de s’appuyer sur un article provenant d’un site web gambien comme preuve, d’autant plus que des fact-checkers ont indiqué que cette information était fausse.