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containerd/cmd/dist/main.go

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cmd/dist: POC implementation of dist fetch With this changeset we introduce several new things. The first is the top-level dist command. This is a toolkit that implements various distribution primitives, such as fetching, unpacking and ingesting. The first component to this is a simple `fetch` command. It is a low-level command that takes a "remote", identified by a `locator`, and an object identifier. Keyed by the locator, this tool can identify a remote implementation to fetch the content and write it back to standard out. By allowing this to be the unit of pluggability in fetching content, we can have quite a bit of flexibility in how we retrieve images. The current `fetch` implementation provides anonymous access to docker hub images, through the namespace `docker.io`. As an example, one can fetch the manifest for `redis` with the following command: ``` $ ./dist fetch docker.io/library/redis latest mediatype:application/vnd.docker.distribution.manifest.v2+json ``` Note that we have provided a mediatype "hint", nudging the fetch implementation to grab the correct endpoint. We can hash the output of that to fetch the same content by digest: ``` $ ./dist fetch docker.io/library/redis sha256:$(./dist fetch docker.io/library/redis latest mediatype:application/vnd.docker.distribution.manifest.v2+json | shasum -a256) ``` Note that the hint is now elided, since we have affixed the content to a particular hash. If you are not yet entertained, let's bring `jq` and `xargs` into the mix for maximum fun. The following incantation fetches the same manifest and downloads all layers into the convenience of `/dev/null`: ``` $ ./dist fetch docker.io/library/redis sha256:a027a470aa2b9b41cc2539847a97b8a14794ebd0a4c7c5d64e390df6bde56c73 | jq -r '.layers[] | .digest' | xargs -n1 -P10 ./dist fetch docker.io/library/redis > /dev/null ``` This is just the beginning. We should be able to centralize configuration around fetch to implement a number of distribution methodologies that have been challenging or impossible up to this point. The `locator`, mentioned earlier, is a schemaless URL that provides a host and path that can be used to resolve the remote. By dispatching on this common identifier, we should be able to support almost any protocol and discovery mechanism imaginable. When this is more solidified, we can roll these up into higher-level operations that can be orchestrated through the `dist` tool or via GRPC. What a time to be alive! Signed-off-by: Stephen J Day <stephen.day@docker.com>
2017-01-20 03:03:44 +00:00
package main
import (
"fmt"
"os"
"github.com/Sirupsen/logrus"
"github.com/docker/containerd"
"github.com/urfave/cli"
)
func main() {
app := cli.NewApp()
app.Name = "dist"
app.Version = containerd.Version
app.Usage = `
___ __
____/ (_)____/ /_
/ __ / / ___/ __/
/ /_/ / (__ ) /_
\__,_/_/____/\__/
distribution tool
`
app.Flags = []cli.Flag{
cli.BoolFlag{
Name: "debug",
Usage: "enable debug output in logs",
},
}
app.Commands = []cli.Command{
fetchCommand,
dist: expand functionality of the dist tool With this change, we add the following commands to the dist tool: - `ingest`: verify and accept content into storage - `active`: display active ingest processes - `list`: list content in storage - `path`: provide a path to a blob by digest - `delete`: remove a piece of content from storage We demonstrate the utility with the following shell pipeline: ``` $ ./dist fetch docker.io/library/redis latest mediatype:application/vnd.docker.distribution.manifest.v2+json | \ jq -r '.layers[] | "./dist fetch docker.io/library/redis "+.digest + "| ./dist ingest --expected-digest "+.digest+" --expected-size "+(.size | tostring) +" docker.io/library/redis@"+.digest' | xargs -I{} -P10 -n1 sh -c "{}" ``` The above fetches a manifest, pipes it to jq, which assembles a shell pipeline to ingest each layer into the content store. Because the transactions are keyed by their digest, concurrent downloads and downloads of repeated content are ignored. Each process is then executed parallel using xargs. Put shortly, this is a parallel layer download. In a separate shell session, could monitor the active downloads with the following: ``` $ watch -n0.2 ./dist active ``` For now, the content is downloaded into `.content` in the current working directory. To watch the contents of this directory, you can use the following: ``` $ watch -n0.2 tree .content ``` This will help to understand what is going on internally. To get access to the layers, you can use the path command: ``` $./dist path sha256:010c454d55e53059beaba4044116ea4636f8dd8181e975d893931c7e7204fffa sha256:010c454d55e53059beaba4044116ea4636f8dd8181e975d893931c7e7204fffa /home/sjd/go/src/github.com/docker/containerd/.content/blobs/sha256/010c454d55e53059beaba4044116ea4636f8dd8181e975d893931c7e7204fffa ``` When you are done, you can clear out the content with the classic xargs pipeline: ``` $ ./dist list -q | xargs ./dist delete ``` Note that this is mostly a POC. Things like failed downloads and abandoned download cleanup aren't quite handled. We'll probably make adjustments around how content store transactions are handled to address this. From here, we'll build out full image pull and create tooling to get runtime bundles from the fetched content. Signed-off-by: Stephen J Day <stephen.day@docker.com>
2017-01-26 22:08:56 +00:00
ingestCommand,
activeCommand,
pathCommand,
deleteCommand,
listCommand,
cmd/dist: POC implementation of dist fetch With this changeset we introduce several new things. The first is the top-level dist command. This is a toolkit that implements various distribution primitives, such as fetching, unpacking and ingesting. The first component to this is a simple `fetch` command. It is a low-level command that takes a "remote", identified by a `locator`, and an object identifier. Keyed by the locator, this tool can identify a remote implementation to fetch the content and write it back to standard out. By allowing this to be the unit of pluggability in fetching content, we can have quite a bit of flexibility in how we retrieve images. The current `fetch` implementation provides anonymous access to docker hub images, through the namespace `docker.io`. As an example, one can fetch the manifest for `redis` with the following command: ``` $ ./dist fetch docker.io/library/redis latest mediatype:application/vnd.docker.distribution.manifest.v2+json ``` Note that we have provided a mediatype "hint", nudging the fetch implementation to grab the correct endpoint. We can hash the output of that to fetch the same content by digest: ``` $ ./dist fetch docker.io/library/redis sha256:$(./dist fetch docker.io/library/redis latest mediatype:application/vnd.docker.distribution.manifest.v2+json | shasum -a256) ``` Note that the hint is now elided, since we have affixed the content to a particular hash. If you are not yet entertained, let's bring `jq` and `xargs` into the mix for maximum fun. The following incantation fetches the same manifest and downloads all layers into the convenience of `/dev/null`: ``` $ ./dist fetch docker.io/library/redis sha256:a027a470aa2b9b41cc2539847a97b8a14794ebd0a4c7c5d64e390df6bde56c73 | jq -r '.layers[] | .digest' | xargs -n1 -P10 ./dist fetch docker.io/library/redis > /dev/null ``` This is just the beginning. We should be able to centralize configuration around fetch to implement a number of distribution methodologies that have been challenging or impossible up to this point. The `locator`, mentioned earlier, is a schemaless URL that provides a host and path that can be used to resolve the remote. By dispatching on this common identifier, we should be able to support almost any protocol and discovery mechanism imaginable. When this is more solidified, we can roll these up into higher-level operations that can be orchestrated through the `dist` tool or via GRPC. What a time to be alive! Signed-off-by: Stephen J Day <stephen.day@docker.com>
2017-01-20 03:03:44 +00:00
}
app.Before = func(context *cli.Context) error {
if context.GlobalBool("debug") {
logrus.SetLevel(logrus.DebugLevel)
}
return nil
}
if err := app.Run(os.Args); err != nil {
fmt.Fprintf(os.Stderr, "dist: %s\n", err)
os.Exit(1)
}
}
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