grootfs

GrootFS: Garden root file system

Note: This repository should be imported as code.cloudfoundry.org/grootfs.

by chattanooga-choochoo

GrootFS is a Cloud Foundry component to satisfy garden-runc's requirements for handling container images.

It is currently under development.

You can find us in the #garden Cloud Foundry slack channel. Use https://slack.cloudfoundry.org to get an invitation.

Installation

Because grootfs depends on Linux kernel features, you can only build it from or to a Linux machine.

mkdir -p $GOPATH/src/code.cloudfoundry.org
git clone https://github.com/cloudfoundry/grootfs.git $GOPATH/src/code.cloudfoundry.org/grootfs
cd $GOPATH/src/code.cloudfoundry.org/grootfs
git submodule update --init --recursive
make

Using go get code.cloudfoundry.org/grootfs is discouraged because it might not work due to our versioned dependencies.

Instructions

Requirements

• Grootfs requires btrfs to be enabled in the kernel, it also makes use of the brtfs-progs (btrfs-tools package on ubuntu) for layering images.

  sudo apt-get install btrfs-tools
  sudo modprobe btrfs # if not loaded
  

• By default all operations will happen in /var/lib/grootfs folder, you can change it by passing the --store flag to the binary. The store folder is expected to be inside a mounted btrfs volume. If you don't have one, you can create a loop mounted btrfs as follows:

  # create a btrfs block device
  truncate -s 1G ~/btrfs_volume
  mkfs.btrfs ~/btrfs_volume
  
  # mount the block device
  sudo mkdir -p /mnt/btrfs
  sudo mount -t btrfs -o user_subvol_rm_allowed ~/btrfs_volume /mnt/btrfs
  sudo btrfs quota enable /mnt/btrfs
  # you might need to chmod/chown the mount point if you don't want to run grootfs as root
  

• For user/group id mapping, you'll also require newuidmap and newgidmap to be installed (uidmap package on ubuntu)

  sudo apt-get install uidmap
  

Creating a bundle

grootfs --store /mnt/btrfs create docker:///ubuntu:latest my-image-id

It also supports local folders as an image source:

grootfs --store /mnt/btrfs create /my-folder my-image-id

This will create a /mnt/btrfs/bundles/my-image-id/rootfs directory with the contents of the image provided.

User/Group ID Mapping

You might want to apply some user and group id mappings to the contents of the rootfs folder. Grootfs supports the --uid-mapping and --gid-mapping arguments. Suppose you are user with uid/gid 1000:

grootfs --store /mnt/btrfs create \
        --uid-mapping 0:1000:1 \
        --uid-mapping 1:100000:650000 \
        --gid-mapping 0:1000:1 \
        --gid-mapping 1:100000:650000 \
        docker:///ubuntu:latest \
        my-image-id

Some important notes:

• If you're not running as root, and you want to use mappings, you'll also need to map root (0:--your-user-id:1)
• Your id mappings can't overlap (e.g. 1:100000:65000 and 100:1000:200)
• You need to have these mappings allowed in the /etc/subuid and /etc/subgid files

Disk Quotas & Drax

Grootfs supports per-filesystem disk-quotas through the Drax binary. BTRFS disk-quotas can only be enabled by a root user, therefore Drax must be owned by root, with the user bit set, and moved somewhere in the $PATH.

make
chown root drax
chmod u+s drax
mv drax /usr/local/bin/

Once Drax is configured, you can apply a quota to the rootfs:

grootfs --store /mnt/btrfs create \
        --disk-limit-size-bytes 10485760 \
        docker:///ubuntu:latest \
        my-image-id

Deleting a bundle

You can destroy a created bundle/rootfs by calling grootfs with the image-id:

grootfs --store /mnt/btrfs delete my-image-id

Logging

By default grootfs will not emit any logging, you can set the log level with the --log-level flag:

grootfs --log-level debug create ...

It also supports redirecting the logs to a log file:

grootfs --log-level debug --log-file /var/log/grootfs.log create ...

Misc

• All devices inside a image are ignored.

Links

• Garden project
• GrootFS Pivotal tracker
• GrootFS CI
• Cloud Foundry Slack - Invitation
• Cloud Foundry Slack