Note_Tech

All technological notes.

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Kubernetes - Storage: Docker Storage

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• Kubernetes - Storage: Docker Storage
  • Docker Storage
    • Storage Driver
  • Docker Volume
    • Volume Drivers

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Docker Storage

• Docker File System:

  • var/lib/docker
    • aufs
    • containers
    • image
    • volumes

• Image Layer Architecture

  • command: docker build
  • Each line of instruction in a Dockerfile creates new layer in the Docker image.
  • Each lay stores the changes from the previous layer.
    • When building an image, Docker tries to reuse the unchanged previous layer and creates only the changed layers.
  • read only
    • Layers are immutable, and get modified only by a new build.

• Container layer:

  • Docker creates a new writable layer on top of the image layers.
  • a read write layer.
  • stores data created by the container.
    • e.g., log files, temporary files, files modified by user.
  • Copy on write mechanism
    • When the file in the image layer gets modified, Docker automatically creates a copy of the image layer in the container layer and enables read / write.
  • live only when the container is running
    • new layer gets destroyed along with container.

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Storage Driver

• the component to enable layered architecture, e.g., create layers, move files across layers
• Common Storage Drivers, depends on the OS
  • AUFS: default in Ubuntu
  • ZFS
  • BTRFS
  • Device Mapper: fedora/ CentOS
  • Overlay
  • Overlay2

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Docker Volume

• Volume

  • used persist the data in Container Layer

• command: docker volume create data_volume

  • File system
    • create a new dir: /var/lib/docker/data_volum

• Volume Mounting

  • mounts a volume from the volumes dir.
  • docker run -v data_volume:/var/lib/mysql mysql
  • if the volume is not created yet, Docker automatically creates the volume

• Bind mounting

  • mount a directory
  • docker run -v /data/mysql:/var/lib/mysql mysql

• --mount: new style with key value pair

docker run --mount type=bind,source=/data/mysqll,target/var/lib/mysql mysql

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Volume Drivers

• volume drivers plugin

  • the component to handle Docker volumes
  • default: local

• Can be specified in the container

# save data in the AWS ebs
docker run -it\
    --name mysql    \
    --volume-driver rexray/ebs  \
    --mount src=ebs-vol,target=/var/lib/mysql   \
    mysql

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