The underlying image remains unchanged.īecause each container has its own writable container layer, and all changes are When the container is deleted, the writable layer is alsoĭeleted. The major difference between a container and an image is the top writable layer.Īll writes to the container that add new or modify existing data are stored in Different storage drivers are available, which have advantagesĪnd disadvantages in different situations. The diagram below shows a container basedĪ storage driver handles the details about the way these layers interact withĮach other. Writing new files, modifying existing files, and deleting files, are written to All changes made to the running container, such as This layer is oftenĬalled the “container layer”. You add a new writable layer on top of the underlying layers. The layers are stacked on top of each other. Sections to learn how to optimize your Dockerfiles for efficient images. Previous layer and add up to the image’s total size. The $HOME/.cache directory is removed, but will still be available in the Note that bothĪdding, and removing files will result in a new layer. Image’s metadata, which does not produce an image layer.Įach layer is only a set of differences from the layer before it. Specifies what command to run within the container, which only modifies the The second RUN command removes a cacheĭirectory, and writes the result to a new layer. The first RUN command builds your application using the make command,Īnd writes the result to a new layer. The COPY command adds some files from your Docker client’s currentĭirectory. The LABEL command only modifies the image’s metadata, and does not produceĪ new layer. The FROM statement starts out by creating a layer from the ubuntu:18.04 Commands that modify the filesystem createĪ layer. # syntax=docker/dockerfile:1 FROM ubuntu:18.04 LABEL COPY. Images and layersĪ Docker image is built up from a series of layers. The volumes section to learn how to use volumes to persist dataĪnd improve performance. Use Docker volumes for write-intensive data, data that must persist beyond theĬontainer’s lifespan, and data that must be shared between containers. Performance overhead, particularly if pre-existing data exists in the read-only Write-intensive applications, such as database storage, are impacted by a Performance, especially for storage drivers that use a copy-on-write filesystem. (depending on the storage driver) write speeds are lower than native file system Storage drivers are optimized for space efficiency, but The container’s writable layer does not persistĪfter the container is deleted, but is suitable for storing ephemeral data that Storage drivers versus Docker volumesĭocker uses storage drivers to store image layers, and to store data in the Your applications and avoid performance problems along the way. Information to make informed choices about the best way to persist data from Stores images, and how these images are used by containers. To use storage drivers effectively, it’s important to know how Docker builds and
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