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additional volume support in building
Signed-off-by: Avi Deitcher <avi@deitcher.net>
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Avi Deitcher
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107
docs/yaml.md
107
docs/yaml.md
@ -18,8 +18,17 @@ For private registries or private repositories on a registry credentials provide
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## Sections
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The configuration file is processed in the order `kernel`, `init`, `onboot`, `onshutdown`,
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`services`, `files`, `volumes`. Each section adds files to the root file system. Sections may be omitted.
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The configuration file is processed in the order:
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1. `kernel`
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1. `init`
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1. `volumes`
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1. `onboot`
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1. `onshutdown`
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1. `services`
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1. `files`
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Each section adds files to the root file system. Sections may be omitted.
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Each container that is specified is allocated a unique `uid` and `gid` that it may use if it
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wishes to run as an isolated user (or user namespace). Anywhere you specify a `uid` or `gid`
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@ -100,8 +109,13 @@ including those in `services`, `onboot` and `onshutdown`. The volumes are create
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chosen by linuxkit at build-time. The volumes then can be referenced by other containers and
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mounted into them.
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Volumes normally are blank directories. If an image is provided, the contents of that image
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will be used to populate the volume.
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Volumes can be in one of several formats:
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* Blank directory: This is the default, and is an empty directory that is created at build-time. It is an overlayfs mount, and can be shared among multiple containers.
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* Image laid out as filesystem: The contents of the image are used to populate the volume. Default format when an image is provided.
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* Image as OCI v1-layout: The image is used as an [OCI v1-layout](https://github.com/opencontainers/image-spec/blob/main/image-layout.md). Indicated by `format: oci`.
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Examples of each are given later in this section.
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The `volumes` section can declare a volume to be read-write or read-only. If the volume is read-write,
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a volume that is mounted into a container can be mounted read-only or read-write. If the volume is read-only,
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@ -111,7 +125,36 @@ By default, volumes are created read-write, and are mounted read-write.
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Volume names **must** be unique, and must contain only lower-case alphanumeric characters, hyphens, and
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underscores.
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Sample `volumes` section:
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#### Samples of `volumes`
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##### Empty directory
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Yaml showing both read-only and read-write:
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```yml
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volumes:
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- name: dira
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readonly: true
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- name: dirb
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readonly: true
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```
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Contents:
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```sh
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$ cd dir && ls -la
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drwxr-xr-x 19 root wheel 608 Sep 30 15:03 .
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drwxrwxrwt 130 root wheel 4160 Sep 30 15:03 ..
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```
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In the above example:
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* `dira` is empty and is read-only.
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* `volb` is empty and is read-write.
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##### Image directory
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Yaml showing both read-only and read-write:
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```yml
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volumes:
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@ -120,8 +163,7 @@ volumes:
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readonly: true
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- name: volb
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image: alpine:latest
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readonly: false
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- name: volc
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format: filesystem # optional, as this is the default format
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readonly: false
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```
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@ -129,7 +171,56 @@ In the above example:
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* `vola` is populated by the contents of `alpine:latest` and is read-only.
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* `volb` is populated by the contents of `alpine:latest` and is read-write.
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* `volc` is an empty volume and is read-write.
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Contents:
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```sh
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$ cd dir && ls -la
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drwxr-xr-x 19 root wheel 608 Sep 30 15:03 .
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drwxrwxrwt 130 root wheel 4160 Sep 30 15:03 ..
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drwxr-xr-x 84 root wheel 2688 Sep 6 14:34 bin
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drwxr-xr-x 2 root wheel 64 Sep 6 14:34 dev
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drwxr-xr-x 37 root wheel 1184 Sep 6 14:34 etc
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drwxr-xr-x 2 root wheel 64 Sep 6 14:34 home
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drwxr-xr-x 13 root wheel 416 Sep 6 14:34 lib
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drwxr-xr-x 5 root wheel 160 Sep 6 14:34 media
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drwxr-xr-x 2 root wheel 64 Sep 6 14:34 mnt
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drwxr-xr-x 2 root wheel 64 Sep 6 14:34 opt
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dr-xr-xr-x 2 root wheel 64 Sep 6 14:34 proc
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drwx------ 2 root wheel 64 Sep 6 14:34 root
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drwxr-xr-x 2 root wheel 64 Sep 6 14:34 run
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drwxr-xr-x 63 root wheel 2016 Sep 6 14:34 sbin
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drwxr-xr-x 2 root wheel 64 Sep 6 14:34 srv
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drwxr-xr-x 2 root wheel 64 Sep 6 14:34 sys
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drwxr-xr-x 2 root wheel 64 Sep 6 14:34 tmp
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drwxr-xr-x 7 root wheel 224 Sep 6 14:34 usr
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drwxr-xr-x 13 root wheel 416 Sep 6 14:34 var
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```
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##### Image OCI Layout
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Yaml showing both read-only and read-write, and both all architectures and a limited subset:
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```yml
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volumes:
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- name: volo
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image: alpine:latest
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format: oci
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readonly: true
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- name: volp
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image: alpine:latest
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readonly: false
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format: oci
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platforms:
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- linux/amd64
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```
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In the above example:
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* `volo` is populated by the contents of `alpine:latest` as an OCI v1-layout for all architectures and is read-only.
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* `volb` is populated by the contents of `alpine:latest` as an OCI v1-layout just for linux/amd64 and is read-write.
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##### Volumes in `services`
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Sample usage of volumes in `services` section:
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@ -16,6 +16,7 @@ import (
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"strings"
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"github.com/containerd/containerd/reference"
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v1 "github.com/google/go-containerregistry/pkg/v1"
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imagespec "github.com/opencontainers/image-spec/specs-go/v1"
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// drop-in 100% compatible replacement and 17% faster than compress/gzip.
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@ -284,9 +285,29 @@ func Build(m moby.Moby, w io.Writer, opts BuildOpts) error {
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lowerPath := strings.TrimPrefix(lower, "/") + "/"
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// get volume tarball from container
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switch {
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case vol.ImageRef() == nil || vol.Format == "" || vol.Format == "filesystem":
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if err := ImageTar(location, vol.ImageRef(), lowerPath, apkTar, resolvconfSymlink, opts); err != nil {
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return fmt.Errorf("failed to build volume filesystem tarball from %s: %v", vol.Name, err)
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}
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case vol.Format == "oci":
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// convert platforms into imagespec platforms
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platforms := make([]imagespec.Platform, len(vol.Platforms))
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for i, p := range vol.Platforms {
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platform, err := v1.ParsePlatform(p)
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if err != nil {
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return fmt.Errorf("failed to parse platform %s: %v", p, err)
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}
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platforms[i] = imagespec.Platform{
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Architecture: platform.Architecture,
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OS: platform.OS,
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Variant: platform.Variant,
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}
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}
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if err := ImageOCITar(location, vol.ImageRef(), lowerPath, apkTar, opts, platforms); err != nil {
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return fmt.Errorf("failed to build volume OCI v1 layout tarball from %s: %v", vol.Name, err)
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}
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}
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// make upper and merged dirs which will be used for mounting
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// no need to make lower dir, as it is made automatically by ImageTar()
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@ -43,7 +43,9 @@ var schema = `
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"properties": {
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"name": {"type": "string"},
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"image": {"type": "string"},
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"readonly": {"type": "boolean"}
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"readonly": {"type": "boolean"},
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"format": {"enum": ["oci","filesystem"]},
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"platforms": {"$ref": "#/definitions/strings"}
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}
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},
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"volumes": {
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