specs

README

Open Container Specifications

This project is where the Open Container Initiative Specifications are written. This is a work in progress. We should have a first draft by end of July 2015.

Table of Contents

• Filesystem Bundle
• Container Configuration
  • Linux Specific Configuration
• Runtime and Lifecycle

Use Cases

To provide context for users the following section gives example use cases for each part of the spec.

Filesystem Bundle & Configuration

• A user can create a root filesystem and configuration, with low-level OS and host specific details, and launch it as a container under an Open Container runtime.

The 5 principles of Standard Containers

Define a unit of software delivery called a Standard Container. The goal of a Standard Container is to encapsulate a software component and all its dependencies in a format that is self-describing and portable, so that any compliant runtime can run it without extra dependencies, regardless of the underlying machine and the contents of the container.

The specification for Standard Containers is straightforward. It mostly defines 1) a file format, 2) a set of standard operations, and 3) an execution environment.

A great analogy for this is the shipping container. Just like how Standard Containers are a fundamental unit of software delivery, shipping containers are a fundamental unit of physical delivery.

1. Standard operations

Just like shipping containers, Standard Containers define a set of STANDARD OPERATIONS. Shipping containers can be lifted, stacked, locked, loaded, unloaded and labelled. Similarly, Standard Containers can be created, started, and stopped using standard container tools (what this spec is about); copied and snapshotted using standard filesystem tools; and downloaded and uploaded using standard network tools.

2. Content-agnostic

Just like shipping containers, Standard Containers are CONTENT-AGNOSTIC: all standard operations have the same effect regardless of the contents. A shipping container will be stacked in exactly the same way whether it contains Vietnamese powder coffee or spare Maserati parts. Similarly, Standard Containers are started or uploaded in the same way whether they contain a postgres database, a php application with its dependencies and application server, or Java build artifacts.

3. Infrastructure-agnostic

Both types of containers are INFRASTRUCTURE-AGNOSTIC: they can be transported to thousands of facilities around the world, and manipulated by a wide variety of equipment. A shipping container can be packed in a factory in Ukraine, transported by truck to the nearest routing center, stacked onto a train, loaded into a German boat by an Australian-built crane, stored in a warehouse at a US facility, etc. Similarly, a standard container can be bundled on my laptop, uploaded to S3, downloaded, run and snapshotted by a build server at Equinix in Virginia, uploaded to 10 staging servers in a home-made Openstack cluster, then sent to 30 production instances across 3 EC2 regions.

4. Designed for automation

Because they offer the same standard operations regardless of content and infrastructure, Standard Containers, just like their physical counterparts, are extremely well-suited for automation. In fact, you could say automation is their secret weapon.

Many things that once required time-consuming and error-prone human effort can now be programmed. Before shipping containers, a bag of powder coffee was hauled, dragged, dropped, rolled and stacked by 10 different people in 10 different locations by the time it reached its destination. 1 out of 50 disappeared. 1 out of 20 was damaged. The process was slow, inefficient and cost a fortune - and was entirely different depending on the facility and the type of goods.

Similarly, before Standard Containers, by the time a software component ran in production, it had been individually built, configured, bundled, documented, patched, vendored, templated, tweaked and instrumented by 10 different people on 10 different computers. Builds failed, libraries conflicted, mirrors crashed, post-it notes were lost, logs were misplaced, cluster updates were half-broken. The process was slow, inefficient and cost a fortune - and was entirely different depending on the language and infrastructure provider.

5. Industrial-grade delivery

There are 17 million shipping containers in existence, packed with every physical good imaginable. Every single one of them can be loaded onto the same boats, by the same cranes, in the same facilities, and sent anywhere in the World with incredible efficiency. It is embarrassing to think that a 30 ton shipment of coffee can safely travel half-way across the World in less time than it takes a software team to deliver its code from one datacenter to another sitting 10 miles away.

With Standard Containers we can put an end to that embarrassment, by making INDUSTRIAL-GRADE DELIVERY of software a reality.

Contributing

Development happens on github for the spec. Issues are used for bugs and actionable items and longer discussions can happen on the mailing list. You can subscribe and join the mailing list on google groups.

The specification and code is licensed under the Apache 2.0 license found in the LICENSE file of this repository.

Weekly Call

The contributors and maintainers of the project have a weekly meeting Wednesdays at 10:00 AM PST. Everyone is welcome to participate in the call. The link to the call will be posted on the mailing list each week along with set topics for discussion. Minutes for the call will be posted to the mailing list for those who are unable to join the call.

Markdown style

To keep consistency throughout the Markdown files in the Open Container spec all files should be formatted one sentence per line. This fixes two things: it makes diffing easier with git and it resolves fights about line wrapping length. For example, this paragraph will span three lines in the Markdown source.

Sign your work

The sign-off is a simple line at the end of the explanation for the patch, which certifies that you wrote it or otherwise have the right to pass it on as an open-source patch. The rules are pretty simple: if you can certify the below (from developercertificate.org):

Developer Certificate of Origin
Version 1.1

Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
660 York Street, Suite 102,
San Francisco, CA 94110 USA

Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.


Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I
    have the right to submit it under the open source license
    indicated in the file; or

(b) The contribution is based upon previous work that, to the best
    of my knowledge, is covered under an appropriate open source
    license and I have the right under that license to submit that
    work with modifications, whether created in whole or in part
    by me, under the same open source license (unless I am
    permitted to submit under a different license), as indicated
    in the file; or

(c) The contribution was provided directly to me by some other
    person who certified (a), (b) or (c) and I have not modified
    it.

(d) I understand and agree that this project and the contribution
    are public and that a record of the contribution (including all
    personal information I submit with it, including my sign-off) is
    maintained indefinitely and may be redistributed consistent with
    this project or the open source license(s) involved.

then you just add a line to every git commit message:

Signed-off-by: Joe Smith <joe@gmail.com>

using your real name (sorry, no pseudonyms or anonymous contributions.)

You can add the sign off when creating the git commit via git commit -s.

Documentation

Index

• Constants
• type BlockIO
• type CPU
• type Hook
• type Hooks
• type HugepageLimit
• type IDMapping
• type InterfacePriority
• type Linux
• type LinuxSpec
• type Memory
• type Mount
• type Namespace
• type Network
• type Platform
• type Process
• type Resources
• type Rlimit
• type Root
• type Spec
• type User

Constants

const Version = "pre-draft"

Version is the specification version that the package types support.

Types

type BlockIO

type BlockIO struct {
	// Specifies per cgroup weight, range is from 10 to 1000
	Weight int64 `json:"blkioWeight"`
	// Weight per cgroup per device, can override BlkioWeight
	WeightDevice string `json:"blkioWeightDevice"`
	// IO read rate limit per cgroup per device, bytes per second
	ThrottleReadBpsDevice string `json:"blkioThrottleReadBpsDevice"`
	// IO write rate limit per cgroup per divice, bytes per second
	ThrottleWriteBpsDevice string `json:"blkioThrottleWriteBpsDevice"`
	// IO read rate limit per cgroup per device, IO per second
	ThrottleReadIOpsDevice string `json:"blkioThrottleReadIopsDevice"`
	// IO write rate limit per cgroup per device, IO per second
	ThrottleWriteIOpsDevice string `json:"blkioThrottleWriteIopsDevice"`
}

BlockIO for Linux cgroup 'blockio' resource management

type CPU

type CPU struct {
	// CPU shares (relative weight vs. other cgroups with cpu shares)
	Shares int64 `json:"shares"`
	// CPU hardcap limit (in usecs). Allowed cpu time in a given period
	Quota int64 `json:"quota"`
	// CPU period to be used for hardcapping (in usecs). 0 to use system default
	Period int64 `json:"period"`
	// How many time CPU will use in realtime scheduling (in usecs)
	RealtimeRuntime int64 `json:"realtimeRuntime"`
	// CPU period to be used for realtime scheduling (in usecs)
	RealtimePeriod int64 `json:"realtimePeriod"`
	// CPU to use within the cpuset
	Cpus string `json:"cpus"`
	// MEM to use within the cpuset
	Mems string `json:"mems"`
}

CPU for Linux cgroup 'cpu' resource management

type Hook

type Hook struct {
	Path string   `json:"path"`
	Args []string `json:"args"`
	Env  []string `json:"env"`
}

Hook specifies a command that is run at a particular event in the lifecycle of a container.

type Hooks

type Hooks struct {
	// Prestart is a list of hooks to be run before the container process is executed.
	// On Linux, they are run after the container namespaces are created.
	Prestart []Hook `json:"prestart"`
	// Poststop is a list of hooks to be run after the container process exits.
	Poststop []Hook `json:"poststop"`
}

type HugepageLimit

type HugepageLimit struct {
	Pagesize string `json:"pageSize"`
	Limit    int    `json:"limit"`
}

HugepageLimit structure corresponds to limiting kernel hugepages

type IDMapping

type IDMapping struct {
	// HostID is the UID/GID of the host user or group
	HostID int32 `json:"hostID"`
	// ContainerID is the UID/GID of the container's user or group
	ContainerID int32 `json:"containerID"`
	// Size is the length of the range of IDs mapped between the two namespaces
	Size int32 `json:"size"`
}

IDMapping specifies UID/GID mappings

type InterfacePriority

type InterfacePriority struct {
	// Name is the name of the network interface
	Name string `json:"name"`
	// Priority for the interface
	Priority int64 `json:"priority"`
}

InterfacePriority for network interfaces

type Linux

type Linux struct {
	// UIDMapping specifies user mappings for supporting user namespaces on Linux
	UIDMappings []IDMapping `json:"uidMappings"`
	// GIDMapping specifies group mappings for supporting user namespaces on Linux
	GIDMappings []IDMapping `json:"gidMappings"`
	// Rlimits specifies rlimit options to apply to the container's process
	Rlimits []Rlimit `json:"rlimits"`
	// Sysctl are a set of key value pairs that are set for the container on start
	Sysctl map[string]string `json:"sysctl"`
	// Resources contain cgroup information for handling resource constraints
	// for the container
	Resources Resources `json:"resources"`
	// Namespaces contains the namespaces that are created and/or joined by the container
	Namespaces []Namespace `json:"namespaces"`
	// Capabilities are Linux capabilities that are kept for the container
	Capabilities []string `json:"capabilities"`
	// Devices are a list of device nodes that are created and enabled for the container
	Devices []string `json:"devices"`
	// RootfsPropagation is the rootfs mount propagation mode for the container
	RootfsPropagation string `json:"rootfsPropagation"`
}

Linux contains platform specific configuration for Linux based containers

type LinuxSpec

type LinuxSpec struct {
	Spec
	// Linux is platform specific configuration for Linux based containers
	Linux Linux `json:"linux"`
}

LinuxSpec is the full specification for Linux containers

type Memory

type Memory struct {
	// Memory limit (in bytes)
	Limit int64 `json:"limit"`
	// Memory reservation or soft_limit (in bytes)
	Reservation int64 `json:"reservation"`
	// Total memory usage (memory + swap); set `-1' to disable swap
	Swap int64 `json:"swap"`
	// Kernel memory limit (in bytes)
	Kernel int64 `json:"kernel"`
	// How aggressive the kernel will swap memory pages. Range from 0 to 100. Set -1 to use system default
	Swappiness int64 `json:"swappiness"`
}

Memory for Linux cgroup 'memory' resource management

type Mount

type Mount struct {
	// Type specifies the mount kind.
	Type string `json:"type"`
	// Source specifies the source path of the mount.  In the case of bind mounts on
	// linux based systems this would be the file on the host.
	Source string `json:"source"`
	// Destination is the path where the mount will be placed relative to the container's root.
	Destination string `json:"destination"`
	// Options are fstab style mount options.
	Options string `json:"options"`
}

Mount specifies a mount for a container.

type Namespace

type Namespace struct {
	// Type is the type of Linux namespace
	Type string `json:"type"`
	// Path is a path to an existing namespace persisted on disk that can be joined
	// and is of the same type
	Path string `json:"path"`
}

Namespace is the configuration for a Linux namespace

type Network

type Network struct {
	// Set class identifier for container's network packets
	ClassID string `json:"classId"`
	// Set priority of network traffic for container
	Priorities []InterfacePriority `json:"priorities"`
}

Network identification and priority configuration

type Platform

type Platform struct {
	// OS is the operating system.
	OS string `json:"os"`
	// Arch is the architecture
	Arch string `json:"arch"`
}

Platform specifies OS and arch information for the host system that the container is created for.

type Process

type Process struct {
	// Terminal creates an interactive terminal for the container.
	Terminal bool `json:"terminal"`
	// User specifies user information for the process.
	User User `json:"user"`
	// Args specifies the binary and arguments for the application to execute.
	Args []string `json:"args"`
	// Env populates the process environment for the process.
	Env []string `json:"env"`
	// Cwd is the current working directory for the process and must be
	// relative to the container's root.
	Cwd string `json:"cwd"`
}

Process contains information to start a specific application inside the container.

type Resources

type Resources struct {
	// DisableOOMKiller disables the OOM killer for out of memory conditions
	DisableOOMKiller bool `json:"disableOOMKiller"`
	// Memory restriction configuration
	Memory Memory `json:"memory"`
	// CPU resource restriction configuration
	CPU CPU `json:"cpu"`
	// BlockIO restriction configuration
	BlockIO BlockIO `json:"blockIO"`
	// Hugetlb limit (in bytes)
	HugepageLimits []HugepageLimit `json:"hugepageLimits"`
	// Network restriction configuration
	Network Network `json:"network"`
}

Resources has container runtime resource constraints

type Rlimit

type Rlimit struct {
	// Type of the rlimit to set
	Type int `json:"type"`
	// Hard is the hard limit for the specified type
	Hard uint64 `json:"hard"`
	// Soft is the soft limit for the specified type
	Soft uint64 `json:"soft"`
}

Rlimit type and restrictions

type Root

type Root struct {
	// Path is the absolute path to the container's root filesystem.
	Path string `json:"path"`
	// Readonly makes the root filesystem for the container readonly before the process is executed.
	Readonly bool `json:"readonly"`
}

Root contains information about the container's root filesystem on the host.

type Spec

type Spec struct {
	// Version is the version of the specification that is supported.
	Version string `json:"version"`
	// Platform is the host information for OS and Arch.
	Platform Platform `json:"platform"`
	// Process is the container's main process.
	Process Process `json:"process"`
	// Root is the root information for the container's filesystem.
	Root Root `json:"root"`
	// Hostname is the container's host name.
	Hostname string `json:"hostname"`
	// Mounts profile configuration for adding mounts to the container's filesystem.
	Mounts []Mount `json:"mounts"`
	// Hooks are the commands run at various lifecycle events of the container.
	Hooks Hooks `json:"hooks"`
}

Spec is the base configuration for the container. It specifies platform independent configuration.

type User

type User struct {
	// Uid is the user id
	UID int32 `json:"uid"`
	// Gid is the group id
	GID int32 `json:"gid"`
	// AdditionalGids are additional group ids set for the container's process
	AdditionalGids []int32 `json:"additionalGids"`
}

User specifies Linux specific user and group information for the container's main process