containerd/images/image.go

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package images
cmd/dist, cmd/ctr: end to end image pull With this changeset, we now have a proof of concept of end to end pull. Up to this point, the relationship between subsystems has been somewhat theoretical. We now leverage fetching, the snapshot drivers, the rootfs service, image metadata and the execution service, validating the proposed model for containerd. There are a few caveats, including the need to move some of the access into GRPC services, but the basic components are there. The first command we will cover here is `dist pull`. This is the analog of `docker pull` and `git pull`. It performs a full resource fetch for an image and unpacks the root filesystem into the snapshot drivers. An example follows: ``` console $ sudo ./bin/dist pull docker.io/library/redis:latest docker.io/library/redis:latest: resolved |++++++++++++++++++++++++++++++++++++++| manifest-sha256:4c8fb09e8d634ab823b1c125e64f0e1ceaf216025aa38283ea1b42997f1e8059: done |++++++++++++++++++++++++++++++++++++++| layer-sha256:3b281f2bcae3b25c701d53a219924fffe79bdb74385340b73a539ed4020999c4: done |++++++++++++++++++++++++++++++++++++++| config-sha256:e4a35914679d05d25e2fccfd310fde1aa59ffbbf1b0b9d36f7b03db5ca0311b0: done |++++++++++++++++++++++++++++++++++++++| layer-sha256:4b7726832aec75f0a742266c7190c4d2217492722dfd603406208eaa902648d8: done |++++++++++++++++++++++++++++++++++++++| layer-sha256:338a7133395941c85087522582af182d2f6477dbf54ba769cb24ec4fd91d728f: done |++++++++++++++++++++++++++++++++++++++| layer-sha256:83f12ff60ff1132d1e59845e26c41968406b4176c1a85a50506c954696b21570: done |++++++++++++++++++++++++++++++++++++++| layer-sha256:693502eb7dfbc6b94964ae66ebc72d3e32facd981c72995b09794f1e87bac184: done |++++++++++++++++++++++++++++++++++++++| layer-sha256:622732cddc347afc9360b4b04b46c6f758191a1dc73d007f95548658847ee67e: done |++++++++++++++++++++++++++++++++++++++| layer-sha256:19a7e34366a6f558336c364693df538c38307484b729a36fede76432789f084f: done |++++++++++++++++++++++++++++++++++++++| elapsed: 1.6 s total: 0.0 B (0.0 B/s) INFO[0001] unpacking rootfs ``` Note that we haven't integrated rootfs unpacking into the status output, but we pretty much have what is in docker today (:P). We can see the result of our pull with the following: ```console $ sudo ./bin/dist images REF TYPE DIGEST SIZE docker.io/library/redis:latest application/vnd.docker.distribution.manifest.v2+json sha256:4c8fb09e8d634ab823b1c125e64f0e1ceaf216025aa38283ea1b42997f1e8059 1.8 kB ``` The above shows that we have an image called "docker.io/library/redis:latest" mapped to the given digest marked with a specific format. We get the size of the manifest right now, not the full image, but we can add more as we need it. For the most part, this is all that is needed, but a few tweaks to the model for naming may need to be added. Specifically, we may want to index under a few different names, including those qualified by hash or matched by tag versions. We can do more work in this area as we develop the metadata store. The name shown above can then be used to run the actual container image. We can do this with the following command: ```console $ sudo ./bin/ctr run --id foo docker.io/library/redis:latest /usr/local/bin/redis-server 1:C 17 Mar 17:20:25.316 # Warning: no config file specified, using the default config. In order to specify a config file use /usr/local/bin/redis-server /path/to/redis.conf 1:M 17 Mar 17:20:25.317 * Increased maximum number of open files to 10032 (it was originally set to 1024). _._ _.-``__ ''-._ _.-`` `. `_. ''-._ Redis 3.2.8 (00000000/0) 64 bit .-`` .-```. ```\/ _.,_ ''-._ ( ' , .-` | `, ) Running in standalone mode |`-._`-...-` __...-.``-._|'` _.-'| Port: 6379 | `-._ `._ / _.-' | PID: 1 `-._ `-._ `-./ _.-' _.-' |`-._`-._ `-.__.-' _.-'_.-'| | `-._`-._ _.-'_.-' | http://redis.io `-._ `-._`-.__.-'_.-' _.-' |`-._`-._ `-.__.-' _.-'_.-'| | `-._`-._ _.-'_.-' | `-._ `-._`-.__.-'_.-' _.-' `-._ `-.__.-' _.-' `-._ _.-' `-.__.-' 1:M 17 Mar 17:20:25.326 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128. 1:M 17 Mar 17:20:25.326 # Server started, Redis version 3.2.8 1:M 17 Mar 17:20:25.326 # WARNING overcommit_memory is set to 0! Background save may fail under low memory condition. To fix this issue add 'vm.overcommit_memory = 1' to /etc/sysctl.conf and then reboot or run the command 'sysctl vm.overcommit_memory=1' for this to take effect. 1:M 17 Mar 17:20:25.326 # WARNING you have Transparent Huge Pages (THP) support enabled in your kernel. This will create latency and memory usage issues with Redis. To fix this issue run the command 'echo never > /sys/kernel/mm/transparent_hugepage/enabled' as root, and add it to your /etc/rc.local in order to retain the setting after a reboot. Redis must be restarted after THP is disabled. 1:M 17 Mar 17:20:25.326 * The server is now ready to accept connections on port 6379 ``` Wow! So, now we are running `redis`! There are still a few things to work out. Notice that we have to specify the command as part of the arguments to `ctr run`. This is because are not yet reading the image config and converting it to an OCI runtime config. With the base laid in this PR, adding such functionality should be straightforward. While this is a _little_ messy, this is great progress. It should be easy sailing from here. Signed-off-by: Stephen J Day <stephen.day@docker.com>
2017-03-18 00:00:52 +00:00
import (
"context"
"encoding/json"
"errors"
"io/ioutil"
"github.com/docker/containerd/content"
"github.com/docker/containerd/log"
digest "github.com/opencontainers/go-digest"
ocispec "github.com/opencontainers/image-spec/specs-go/v1"
)
// Image provides the model for how containerd views container images.
type Image struct {
Name string
Descriptor ocispec.Descriptor
}
// TODO(stevvooe): Many of these functions make strong platform assumptions,
// which are untrue in a lot of cases. More refactoring must be done here to
// make this work in all cases.
// Config resolves the image configuration descriptor.
//
// The caller can then use the descriptor to resolve and process the
// configuration of the image.
func (image *Image) Config(ctx context.Context, provider content.Provider) (ocispec.Descriptor, error) {
var configDesc ocispec.Descriptor
return configDesc, Walk(ctx, HandlerFunc(func(ctx context.Context, desc ocispec.Descriptor) ([]ocispec.Descriptor, error) {
switch image.Descriptor.MediaType {
case MediaTypeDockerSchema2Manifest, ocispec.MediaTypeImageManifest:
rc, err := provider.Reader(ctx, image.Descriptor.Digest)
if err != nil {
return nil, err
}
defer rc.Close()
p, err := ioutil.ReadAll(rc)
if err != nil {
return nil, err
}
var manifest ocispec.Manifest
if err := json.Unmarshal(p, &manifest); err != nil {
return nil, err
}
configDesc = manifest.Config
return nil, nil
default:
return nil, errors.New("could not resolve config")
}
}), image.Descriptor)
}
// RootFS returns the unpacked diffids that make up and images rootfs.
//
// These are used to verify that a set of layers unpacked to the expected
// values.
func (image *Image) RootFS(ctx context.Context, provider content.Provider) ([]digest.Digest, error) {
desc, err := image.Config(ctx, provider)
if err != nil {
return nil, err
}
p, err := content.ReadBlob(ctx, provider, desc.Digest)
if err != nil {
log.G(ctx).Fatal(err)
}
var config ocispec.Image
if err := json.Unmarshal(p, &config); err != nil {
log.G(ctx).Fatal(err)
}
// TODO(stevvooe): Remove this bit when OCI structure uses correct type for
// rootfs.DiffIDs.
var diffIDs []digest.Digest
for _, diffID := range config.RootFS.DiffIDs {
diffIDs = append(diffIDs, digest.Digest(diffID))
}
return diffIDs, nil
}