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Extending containerd (KubeCon/CloudNativeCon NA 2019)

Samuel Karp
November 19, 2019
470

Extending containerd (KubeCon/CloudNativeCon NA 2019)

containerd, a graduated CNCF project, is a widely used container runtime that provides core functionality for Docker. containerd was designed to be small and simple, but also very modular and extensible. This talk covers the architecture of containerd, explains the responsibilities of each component, and dives deep into containerd’s facility for extension. We’ll cover the individual gRPC services that make up containerd and show how they can be extended with proxy plugins, Go plugins, process interfaces (OCI runtimes and process-based logging), thick client implementations, and build-your-own containerd for compiled-in extension. These extension mechanisms can be shown with simple examples and real-world use in the firecracker-containerd project.

Presented with Maksym Pavlenko

Samuel Karp

November 19, 2019
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Transcript

  1. Samuel Karp – @samuelkarp
    Maksym Pavlenko – @mak_pav
    Extending containerd

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  2. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Table of contents
    • What is containerd?
    • Core modularity
    • Extension
    • Examples!

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  3. © 2019, Amazon Web Services, Inc. or its Affiliates.
    © 2019, Amazon Web Services, Inc. or its Affiliates.
    containerd

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  4. © 2019, Amazon Web Services, Inc. or its Affiliates.
    What is containerd?

    Small and focused container
    runtime

    Build on lessons from Docker

    Strict scope to limit features

    Modular, composable pieces

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  5. © 2019, Amazon Web Services, Inc. or its Affiliates.
    The containerd stack

    gRPC API and Services

    Storage services
    – Content store
    – Snapshotters

    Runtime (runc, OCI, v2)
    gRPC Metrics
    Storage
    Content Snapshot Diff
    Metadata
    Images Containers Tasks Events
    Runtimes
    Runtimes

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  6. © 2019, Amazon Web Services, Inc. or its Affiliates.
    The containerd stack

    gRPC API and Services

    Storage services
    – Content store
    – Snapshotters

    Runtime (runc, OCI, v2)
    gRPC Metrics
    Storage
    Content Snapshot Diff
    Metadata
    Images Containers Tasks Events
    Runtimes
    Runtimes

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  7. © 2019, Amazon Web Services, Inc. or its Affiliates.
    The containerd stack

    gRPC API and Services

    Storage services
    – Content store
    – Snapshotters

    Runtime (runc, OCI, v2)
    gRPC Metrics
    Storage
    Content Snapshot Diff
    Metadata
    Images Containers Tasks Events
    Runtimes
    Runtimes

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  8. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Container image layers

    A copy-on-write view of files

    New files exist in the top layer

    Modified files are “copied up”

    Unmodified files stay in
    original layer

    Deleted files are hidden, not
    removed
    Top layer
    (read-write)
    Intermediate
    layer
    (read-only)
    Base layer
    (read-only)

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  9. © 2019, Amazon Web Services, Inc. or its Affiliates.
    The containerd stack

    gRPC API and Services

    Storage services
    – Content store
    – Snapshotters

    Runtime (runc, OCI, v2)
    gRPC Metrics
    Storage
    Content Snapshot Diff
    Metadata
    Images Containers Tasks Events
    Runtimes
    Runtimes

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  10. © 2019, Amazon Web Services, Inc. or its Affiliates.
    The containerd stack

    gRPC API and Services

    Storage services
    – Content store
    – Snapshotters

    Runtime (runc, OCI, v2)
    gRPC Metrics
    Storage
    Content Snapshot Diff
    Metadata
    Images Containers Tasks Events
    Runtimes
    Runtimes

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  11. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Core modularity

    Small, separate services

    Use services together for higher-level functionality

    Services modeled with interfaces

    Services are implemented as plugins

    Client library to tie it all together

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  12. © 2019, Amazon Web Services, Inc. or its Affiliates.
    © 2019, Amazon Web Services, Inc. or its Affiliates.
    Extension

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  13. © 2019, Amazon Web Services, Inc. or its Affiliates.
    containerd extension points

    Client library extensions

    “CLI”/executable plugins

    gRPC proxy plugins

    Go plugins

    Built-in plugins

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  14. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Client library extensions

    “Smart” client in Go provides
    interfaces

    Write your own
    implementations when you
    want something different!

    Requires that you control the
    client code

    Examples
    – Pulling images
    – I/O handling for containers

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  15. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Client library extensions – Pulling images

    Pulling images happens in the
    client library

    Network access and protocol
    support

    Default implementation is
    Docker registry

    Examples
    – Distributed/peer-to-peer
    protocol like BitTorrent
    – Other registry protocols like
    Amazon ECR
    – Maybe you want to store
    images in git-lfs?
    – Anything you can think of!

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  16. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Client library extension – default resolver
    img, err := client.Pull(
    namespaces.NamespaceFromEnv(ctx),
    "my.registry/myrepository:mytag",
    containerd.WithPullUnpack)

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  17. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Client library extension – Amazon ECR resolver
    // import "github.com/awslabs/amazon-ecr-containerd-resolver"
    resolver, _ := ecr.NewResolver()
    img, err := client.Pull(
    namespaces.NamespaceFromEnv(ctx),
    "ecr.aws/arn:aws:ecr:us-west-2:123456789012:repository/myrepository:mytag",
    containerd.WithResolver(resolver),
    containerd.WithPullUnpack)

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  18. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Client library extension – Resolver interface
    type Resolver interface {
    Resolve(ctx context.Context, ref string) (string, oci.Descriptor, error)
    Fetcher(ctx context.Context, ref string) (Fetcher, error)
    Pusher(ctx context.Context, ref string) (Pusher, error)
    }

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  19. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Client library extension – Resolver interface
    type Resolver interface {
    Resolve(ctx context.Context, ref string) (string, oci.Descriptor, error)
    Fetcher(ctx context.Context, ref string) (Fetcher, error)
    Pusher(ctx context.Context, ref string) (Pusher, error)
    }
    type Fetcher interface {
    Fetch(ctx context.Context, desc oci.Descriptor) (io.ReadCloser, error)
    }

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  20. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Client library extension – Resolver interface
    type Resolver interface {
    Resolve(ctx context.Context, ref string) (string, oci.Descriptor, error)
    Fetcher(ctx context.Context, ref string) (Fetcher, error)
    Pusher(ctx context.Context, ref string) (Pusher, error)
    }
    type Fetcher interface {
    Fetch(ctx context.Context, desc oci.Descriptor) (io.ReadCloser, error)
    }
    type Pusher interface {
    Push(ctx context.Context, desc oci.Descriptor) (content.Writer, error)
    }

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  21. © 2019, Amazon Web Services, Inc. or its Affiliates.
    “CLI”/executable plugins

    Command-line interface
    conventions

    Separate program from
    containerd

    containerd defines semantics
    for STDIO, flags, working
    directory, file names, etc

    Examples
    – Runtimes (OCI and “v2”)
    – Log forwarding
    – Stream processing/media
    transformation

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  22. © 2019, Amazon Web Services, Inc. or its Affiliates.
    “CLI”/executable plugins – Runtimes
    runc firecracker-containerd
    Default runtime
    Linux containers
    Alternative runtime
    Firecracker microVMs
    Adheres to OCI standard Adheres to containerd “v2” interface
    Specification covers:

    command-line arguments/flags

    working directory

    input files

    exit codes
    Specification covers:

    command-line arguments/flags

    working directory

    input files

    gRPC/ttrpc on a Unix domain socket

    exit codes

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  23. © 2019, Amazon Web Services, Inc. or its Affiliates.
    “CLI”/executable plugins – “v2” runtimes

    Binary prefixes with containerd-shim-foo-bar

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  24. © 2019, Amazon Web Services, Inc. or its Affiliates.
    “CLI”/executable plugins – “v2” runtimes

    Binary prefixes with containerd-shim-foo-bar

    Be located within PATH

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  25. © 2019, Amazon Web Services, Inc. or its Affiliates.
    “CLI”/executable plugins – “v2” runtimes

    Binary prefixes with containerd-shim-foo-bar

    Be located within PATH

    Define program lifecycle through start and delete arguments

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  26. © 2019, Amazon Web Services, Inc. or its Affiliates.
    “CLI”/executable plugins – “v2” runtimes
    $ containerd-shim-foo-bar start
    /path/to/socket.sock
    $ containerd-shim-foo-bar delete

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  27. © 2019, Amazon Web Services, Inc. or its Affiliates.
    “CLI”/executable plugins – “v2” runtimes

    Binary prefixes with containerd-shim-foo-bar

    Be located within PATH

    Define program lifecycle through start and delete arguments

    Implement TaskService as a ttrpc service

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  28. © 2019, Amazon Web Services, Inc. or its Affiliates.
    “CLI”/executable plugins – “v2” runtimes
    type TaskService interface {
    State(context.Context, *StateRequest) (*StateResponse, error)
    Create(context.Context, *CreateTaskRequest) (*CreateTaskResponse, error)
    Start(context.Context, *StartRequest) (*StartResponse, error)
    Delete(context.Context, *DeleteRequest) (*DeleteResponse, error)
    Pids(context.Context, *PidsRequest) (*PidsResponse, error)
    Pause(context.Context, *PauseRequest) (*types1.Empty, error)
    Resume(context.Context, *ResumeRequest) (*types1.Empty, error)
    Kill(context.Context, *KillRequest) (*types1.Empty, error)
    Exec(context.Context, *ExecProcessRequest) (*types1.Empty, error)
    Update(context.Context, *UpdateTaskRequest) (*types1.Empty, error)
    Wait(context.Context, *WaitRequest) (*WaitResponse, error)

    }

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  29. © 2019, Amazon Web Services, Inc. or its Affiliates.
    “CLI”/executable plugins – “v2” runtimes

    Binary prefixes with containerd-shim-foo-bar

    Be located within PATH

    Define program lifecycle through start and delete arguments

    Implement TaskService as a ttrpc service

    Can use containerd’s shim helpers

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  30. © 2019, Amazon Web Services, Inc. or its Affiliates.
    “CLI”/executable plugins – “v2” runtimes
    func main() {
    shim.Run("foo.bar", myShim)
    }
    func myShim(
    ctx context.Context,
    id string,
    publisher shim.Publisher,
    callback func(),
    ) (shim.Shim, error){
    // my implementation here!
    }

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  31. © 2019, Amazon Web Services, Inc. or its Affiliates.
    “CLI”/executable plugins – “v2” runtimes

    Binary prefixes with containerd-shim-foo-bar

    Be located within PATH

    Define program lifecycle through start and delete arguments

    Implement TaskService as a ttrpc service

    Can use containerd’s shim helpers

    sudo ctr run \
    --runtime foo.bar \
    docker.io/library/hello-world:latest \
    my-hello-world-container

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  32. © 2019, Amazon Web Services, Inc. or its Affiliates.
    gRPC proxy plugins

    Plugins run as separate processes

    Expose the service API over a Unix domain socket

    containerd acts as a pass-through

    Proxy plugin registered in containerd’s config file

    Snapshot and content services supported as proxy plugins

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  33. © 2019, Amazon Web Services, Inc. or its Affiliates.
    gRPC proxy plugins - Snapshotters

    Snapshotters provide image-
    and container-filesystems

    Many implement a form of
    copy-on-write

    Several built in to containerd

    Out-of-process gRPC proxy
    plugins enable new
    development

    Examples
    – Block-device snapshotters:
    devicemapper and lvm
    – Ongoing discussion about
    network-based snapshotters

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  34. © 2019, Amazon Web Services, Inc. or its Affiliates.
    gRPC proxy plugins - Snapshotters

    Implement Snapshotter as a gRPC service

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  35. © 2019, Amazon Web Services, Inc. or its Affiliates.
    gRPC proxy plugins - Snapshotters
    type Snapshotter interface {
    Stat(context.Context, string) (Info, error)
    Update(context.Context, Info, ...string) (Info, error)
    Usage(context.Context, string) (Usage, error)
    Mounts(context.Context, string) ([]mount.Mount, error)
    Prepare(context.Context, string, string, ...Opt) ([]mount.Mount, error)
    View(context.Context, string, string, ...Opt) ([]mount.Mount, error)
    Commit(context.Context, string, string, ...Opt) error
    Remove(context.Context, string) error
    Walk(context.Context, func(context.Context, Info) error) error
    Close() error
    }

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  36. © 2019, Amazon Web Services, Inc. or its Affiliates.
    gRPC proxy plugins - Snapshotters

    Implement Snapshotter as a gRPC service

    Registered in containerd configuration

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  37. © 2019, Amazon Web Services, Inc. or its Affiliates.
    gRPC proxy plugins - Snapshotters
    [proxy_plugins]
    [proxy_plugins.foo-snapshotter]
    type = "snapshot"
    Address = "/var/run/foo-snapshotter.sock"

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  38. © 2019, Amazon Web Services, Inc. or its Affiliates.
    gRPC proxy plugins - Snapshotters

    Implement Snapshotter as a gRPC service

    Registered in containerd configuration

    sudo ctr run \
    --snapshotter foo-snapshotter \
    docker.io/library/hello-world:latest \
    my-hello-world-container

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  39. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Go plugins

    Similar power/flexibility to
    built-in plugins

    Can add at runtime

    Loaded from containerd’s
    plugins folder (or configured
    folder)

    Name includes OS,
    architecture, and OS-specific
    extension:
    myplugin-linux-amd64.so

    Strongly tied to how
    containerd was built
    – OS, architecture
    – Version of Go
    – Versions of every common
    package

    You’re responsible for ensuring
    compatible build environment

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  40. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Built-in plugins

    Default plugins are (mostly!)
    built-in

    In the source tree of
    containerd

    Can’t add at runtime

    Most powerful/flexible

    Most effort required

    Examples
    – Default snapshotters
    – Default content store
    – Default diff service
    – Default image service
    – Default container service
    – CRI plugin

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  41. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Built-in plugins – Build your own

    Build in your own plugins

    ...by building your own containerd binary

    You don’t have to fork containerd!

    You solve your own build environment and distribution

    You’re responsible for keeping up to date

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  42. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Built-in plugins – Build your own

    Write your own main() function

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  43. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Built-in plugins – Build your own
    func main() {
    app := command.App()
    if err := app.Run(os.Args); err != nil {
    fmt.Fprintf(os.Stderr, "containerd: %s\n", err)
    os.Exit(1)
    }
    }

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  44. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Built-in plugins – Build your own

    Write your own main() function

    import the plugins you want

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  45. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Built-in plugins – Build your own
    import (
    // main function
    "github.com/containerd/containerd/cmd/containerd/command"
    // builtins, see
    // https://github.com/containerd/containerd/blob/master/cmd/containerd/builtins.go
    _ "github.com/containerd/containerd/diff/walking/plugin"
    _ "github.com/containerd/containerd/gc/scheduler"
    _ "github.com/containerd/containerd/runtime/restart/monitor"
    _ "github.com/containerd/containerd/services/containers"
    _ "github.com/containerd/containerd/services/content"
    _ "github.com/containerd/containerd/services/diff"
    _ "github.com/containerd/containerd/services/events"
    _ "github.com/containerd/containerd/services/healthcheck"
    _ "github.com/containerd/containerd/services/images"
    _ "github.com/containerd/containerd/services/introspection"
    _ "github.com/containerd/containerd/services/leases"
    _ "github.com/containerd/containerd/services/namespaces"

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  46. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Built-in plugins – Build your own
    _ "github.com/containerd/containerd/services/opt"
    _ "github.com/containerd/containerd/services/snapshots"
    _ "github.com/containerd/containerd/services/tasks"
    _ "github.com/containerd/containerd/services/version"
    // Linux builtins, see
    // https://github.com/containerd/containerd/blob/master/cmd/containerd/builtins_linux.go
    _ "github.com/containerd/containerd/metrics/cgroups"
    _ "github.com/containerd/containerd/runtime/v1/linux"
    _ "github.com/containerd/containerd/runtime/v2"
    _ "github.com/containerd/containerd/runtime/v2/runc/options"
    // snapshotters
    _ "github.com/containerd/containerd/snapshots/devmapper"
    _ "github.com/containerd/containerd/snapshots/overlay"
    // Your plugin!
    _ "github.com/foobar/foobar/foobar-api”
    )

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  47. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Built-in plugins – Build your own

    Write your own main() function

    import the plugins you want

    Register your plugin with init()

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  48. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Built-in plugins – Build your own
    func init() {
    plugin.Register(&plugin.Registration{
    Type: plugin.ServicePlugin,
    ID: "myPlugin.ID",
    Requires: []plugin.Type{
    plugin.MetadataPlugin,
    },
    InitFn: func(ic *plugin.InitContext) (interface{}, error) {
    // Init your plugin here
    },
    })
    }

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  49. © 2019, Amazon Web Services, Inc. or its Affiliates.
    © 2019, Amazon Web Services, Inc. or its Affiliates.
    Demo!

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  50. © 2019, Amazon Web Services, Inc. or its Affiliates.
    Demo summary

    Pull image from Amazon ECR with
    amazon-ecr-containerd-resolver client library extension

    Custom containerd binary with firecracker-control built-in plugin

    devmapper snapshotter (now embedded, former gRPC proxy plugin)

    containerd-shim-aws-firecracker runtime (executable plugin) to
    run Firecracker microVMs

    Inside VM, use containerd-shim-runc-v1 (default runtime) for runc

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  51. © 2019, Amazon Web Services, Inc. or its Affiliates.
    © 2019, Amazon Web Services, Inc. or its Affiliates.
    Q&A
    Samuel Karp and Maksym Pavlenko

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  52. © 2019, Amazon Web Services, Inc. or its Affiliates.
    A brief note before we finish —
    Session surveys provide valuable information to speakers
    Feedback that is very helpful:

    Topics you were excited to learn about

    Suggestions for improving understanding and clarity
    Feedback that is extremely unhelpful:

    Comments unrelated to talk content (please refer to the CNCF Code of Conduct)
    The “hallway track” is always open!
    Feedback and questions welcome

    [email protected] or @samuelkarp

    [email protected] or @mak_pav
    For support, use the AWS Forums or contact AWS Support

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  53. © 2019, Amazon Web Services, Inc. or its Affiliates.
    © 2019, Amazon Web Services, Inc. or its Affiliates.
    Thank you!
    Samuel Karp (@samuelkarp)
    Maksym Pavlenko (@mak_pav)

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