grootfs

README

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.

Index

• Installation
• Configuration
• Initializing a store
• Deleting a store
• Create an image
• Delete an image
• Stats
• Clean up
• Logging
• Metrics
• Running tests in Concourse
• Known Issues

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.

Filesystems

GrootFS makes use of various Linux filesystem features in order to efficiently store container root filesystems on the host machine.

Currently we support:

• BTRFS (--driver btrfs)
• Overlay on XFS (--driver overlay-xfs)

GrootFS's 'store' directory must be stored on one of these filesystems. Our setup script will try to set up both of these filesystems for you so you can experiment with GrootFS, or you can provision your own and configure GrootFS to point to the mounted filesystem you create, using the --store and --driver command-line flags. These are documented in the instructions below.

Instructions

Requirements

sudo hack/quick-setup

We assume that:

• You are running a Debian/Ubuntu based system with BTRFS and XFS enabled in the kernel

This will:

• Install the userspace tools required to use GrootFS on either BTRFS or XFS
• Create a BTRFS filesystem and mount it under /var/lib/grootfs/btrfs
• Create an XFS filesystem and mount it under /var/lib/grootfs/xfs

By default all operations will happen in the /var/lib/grootfs folder. You can change this by passing the --store flag to the grootfs binary. The store folder is expected to be inside either of the mounted BTRFS or XFS volumes. You will also need to pass the --driver option with a value of either btrfs or overlay-xfs accordingly.

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

Configuration

GrootFS can optionally be configured with a YAML config file. If both a config file and command line arguments are provided, the command line arguments will take precedence.

To use a config file:

grootfs --config ./my-config.yml <command> ...

Following is an example configuration file with all options provided:

store: /var/lib/data/grootfs/store
driver: btrfs
btrfs_bin: /var/lib/packages/btrfs-progs/bin/btrfs
drax_bin: /var/lib/packages/grootfs/bin/drax
newuidmap_bin: /var/lib/packages/idmapper/bin/newuidmap
newgidmap_bin: /var/lib/packages/idmapper/bin/newgidmap
log_level: debug
metron_endpoint: 127.0.0.1:8081
clean:
  threshold_bytes: 1048576
  ignore_images:
    - docker:///ubuntu
    - docker://my-docker-registry.example.com:1234/busybox
create:
  insecure_registries:
  - my-docker-registry.example.com:1234
  with_clean: true
  uid_mappings:
  - "0:4294967294:1"
  - "1:1:4294967293"
  gid_mappings:
  - "0:4294967294:1"
  - "1:1:4294967293"

Key	Description
store	Path to the store directory
driver	Filesystem driver to use <btrfs | overlay-xfs>
btrfs_bin	Path to btrfs bin. (If not provided will use $PATH)
drax_bin	Path to drax bin. (If not provided will use $PATH)
newuidmap_bin	Path to newuidmap bin. (If not provided will use $PATH)
newgidmap_bin	Path to newgidmap bin. (If not provided will use $PATH)
log_level	Set logging level <debug | info | error | fatal>
metron_endpoint	Metron endpoint used to send metrics
create.insecure_registries	Whitelist a private registry
create.with_clean	Clean up unused layers before creating rootfs
create.uid_mappings	UID mapping for image translation, e.g.: <Namespace UID>:<Host UID>:<Size>
create.gid_mappings	GID mapping for image translation, e.g.: <Namespace GID>:<Host GID>:<Size>
create.without_mount	Don't perform the rootfs mount.
clean.ignore_images	Images to ignore during cleanup
clean.threshold_bytes	Disk usage of the store directory at which cleanup should trigger

Initializing a store

You can create a store directory within a mountpath for your images:

grootfs --store /mnt/xfs/my-store-dir --driver overlay-xfs init-store <--uid-mapping 1000:0:1> <--gid-mapping 1000:0:1> <--uid-mapping/gid-mapping ...>

N.B.

• This command is new and as yet incomplete. Therefore we assume the path you are giving to store is already within a mounted directory.
• The driver you pass to init-store must be compatible with the mounted path.
• The command can currently only be run as root, with the mounted store owned by root.
• It can take a number of uid/gid mappings to initialize the store with.
• If no mappings are provided, the store will be owned by host root user.
• If mappings are provided, the store will be owned by the namespace root user specified.
• Eventually this command will create a mounted filesystem for you, and will allow multiple independent stores to be set within one mount.

Deleting a store

You can delete a store by running the following:

While this command will delete all contents of the store path, it will leave the backing filesystem intact.

grootfs --store /mnt/btrfs/my-store-dir --driver btrfs delete-store

Creating an image

You can create a rootfs image based on a remote docker image:

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

Or from a local tar file as an image source:

grootfs --store /mnt/btrfs create /my-rootfs.tar my-image-id

Output

The output of this command is a json object which has the following structure:

{
  "rootfs": "...", # complete path to the image rootfs, which lives in <image-path>/rootfs
  "config": {...}, # contents of image config, also writen to <image-path>/image.json
}

• The <image-path>/rootfs folder is where the root filesystem lives.
• The <image-path>/image.json file follows the OCI image description schema.

If the --without-mount flag is provided (or create.without_mount = true in config), the json output will also contain the mount key:

  ...
  "mount": {
    "destination": "/path/to/rootfs",
    "type": "overlay",
    "source": "overlay",
    "options": ["lowerdir=..."]
  }
  ...

The --without-mount option exists so that GrootFS can be run as non-root. The mount information is compatible with OCI container spec.

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 an image

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

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

Or the rootfs image path:

grootfs --store /mnt/btrfs delete /mnt/btrfs/images/<uid>/my-image-id

Caveats:

The store is based on the effective user running the command. If the user tries to delete a rootfs image that does not belong to her/him the command fails.

Stats

You can get stats from an image by calling grootfs stats with the image-id:

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

Or the image path:

grootfs --store /mnt/btrfs delete /mnt/btrfs/images/<uid>/my-image-id

This will result in a JSON object of the following form:

{
  "disk_usage": {
    "total_bytes_used": 132169728,
    "exclusive_bytes_used": 16384
  }
}

total_bytes_used refers to the total space the image takes. exclusive_bytes_used is the amount of space the image takes excluding the base image, i.e.: just the container data.

Clean up

grootfs --store /mnt/btrfs clean

When clean is called, any layers that aren't being used by a rootfs that currently exists are deleted from the store*.

For example: Imagine that we create two rootfs images from different base images, Image A and Image B:

- Image A
  Layers:
    - layer-1
    - layer-2
    - layer-3

- Image B
  Layers:
    - layer-1
    - layer-4
    - layer-5

They have a layer in common, layer-1. And after deleting Image B, layer-4 and layer-5 can be collected by clean, but not layer-1 because Image A still uses that layer.

It is safe to run the command in parallel, it does not interfere with other creations or deletions.

The clean command has an optional integer parameter, threshold-bytes, and when the store* size is under that clean is a no-op, it does not remove anything. On the other hand, if the store* is over the threshold it cleans up any resource that is not being used. If 0 is provided it will behave the same way as if the flag wasn't specified, it will clean up everything that's not being used. If a non integer or negative integer is provided, the command fails without cleaning up anything.

Caveats:

The store is based on the effective user running the command. If the user tries to clean up a store that does not belong to her/him the command fails.

* It takes only into account the cache and volumes folders in the store.

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 ...

Metrics

GrootFS emits the following metrics with each command. These are emitted via Dropsonde to the Metron Agent and can be integrated with a monitoring application e.g. Datadog.

Create

Metric Name	Units	Description
ImageCreationTime	nanos	Total duration of Image Creation
UnpackTime	nanos	Total time taken to unpack the base image tarball
FailedUnpackTime	nanos	Same as above but emitted on failure
StoreUsage	bytes	Total bytes in use in the Store at the end of the command
LockingTime	nanos	Total time the store lock is held by the command
grootfs-create.run	int	Cumulative count of Create executions
grootfs-create.fail	int	Cumulative count of failed Create executions
grootfs-create.success	int	Cumulative count of successful Create executions
grootfs-error.create		Emits when an error has occurred

Clean

Metric Name	Units	Description
ImageCleanTime	nanos	Total duration of Clean
StoreUsage	bytes	Total bytes in use in the Store at the end of the command
LockingTime	nanos	Total time the store lock is held by the command
grootfs-clean.run	int	Cumulative count of Clean executions
grootfs-clean.fail	int	Cumulative count of failed Clean executions
grootfs-clean.success	int	Cumulative count of successful Clean executions
grootfs-error.clean		Emits when an error has occurred

Delete

Metric Name	Units	Description
ImageDeletionTime	nanos	Total duration of Image Deletion
grootfs-delete.run	int	Cumulative count of Delete executions
grootfs-delete.fail	int	Cumulative count of failed Delete executions
grootfs-delete.success	int	Cumulative count of successful Delete executions
grootfs-error.delete		Emits when an error has occurred

Stats

Metric Name	Units	Description
ImageStatsTime	nanos	Total duration of retrieving Image Stats
grootfs-stats.run	int	Cumulative count of Stats executions
grootfs-stats.fail	int	Cumulative count of failed Stats executions
grootfs-stats.success	int	Cumulative count of successful Stats executions
grootfs-error.stats		Emits when an error has occurred

Running tests in Concourse

GrootFS uses Concourse for both Continuous Integration (CI) and testing. One way of running tests locally is with concourse-lite, which is a Vagrant box.

Starting Concourse Lite

vagrant box add concourse/lite
vagrant init concourse/lite
vagrant up

Running tests

make concourse-test

Known Issues

Restrictions when running as a non-root user

• GrootFS cannot use docker:///centos when run as a non-root user without UID/GID mappings. CentOS sets the /root permissions to 0550 (i.e.: r-xr-x---) and therefore, when GrootFS runs as a non-root user it cannot write files into the rootfs /root. You can work around this by either running as root or using a UID/GID mapping.

• You must mount the btrfs volume with -o user_subvol_rm_allowed or you won't be able to delete images or clean up after failure scenarios.

• Files not visible to the calling user in the base image won't be in the resulting rootfs.

• The store must have the right permissions or ownership for the calling user otherwise the command will fail.

• The calling user can only delete the rootfs that it owns.

• The calling user can only cleanup the cached volumes that it owns.

• The calling user can only request stats for the rootfs that it owns.

Misc

• All devices inside a image are ignored.

Links

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