Images and Layers
Naming scheme
Format: <registry>/<repository>:<tag>
<repository> describes purpose
<tag> describes variant or version
<repository>:<tag> is called an image
Docker Hub
On Docker Hub: <repository>:<tag>
Official image: alpine:stable
Community image: nicholasdille/insulatr
Images and layers
Images consist of layers
Layers improve download performance
Layers enable reusability
Image Manifest
Lists layers in the image
Layers are referenced as blobs
References are SHA256 hashed: sha256:...
Image configuration
Contains command used to create layers
Stored as blob
Demo: Layers 020_advanced/030_layers
Upload image to local registry
Build and push image:
docker run -d -p 127.0.0.1:5000:5000 registry:2
docker build --tag localhost:5000/hello-world-java .
docker push localhost:5000/hello-world-java
Check layers:
docker history localhost:5000/hello-world-java
Analyze layers:
dive hello-world-java
https://github.com/wagoodman/dive
Demo: Image Manifest 020_advanced/030_layers
Fetch image manifest:
curl http://localhost:5000/v2/hello-world-java/manifests/latest \
--silent \
--header "Accept: application/vnd.docker.distribution.manifest.v2+json" \
| jq
Demo: Image Configuration 020_advanced/030_layers
Fetch image configuration:
DIGEST=$(
curl http://localhost:5000/v2/hello-world-java/manifests/latest \
--silent \
--header "Accept: application/vnd.docker.distribution.manifest.v2+json" \
| jq --raw-output '.config.digest'
)
curl http://localhost:5000/v2/hello-world-java/blobs/${DIGEST} \
--silent \
--header "Accept: application/vnd.docker.container.image.v1+json" \
| jq
Demo: Download image layer 020_advanced/030_layers
Fetch digest of last layer:
DIGEST=$(
curl http://localhost:5000/v2/hello-world-java/manifests/latest \
--silent \
--header "Accept: application/vnd.docker.distribution.manifest.v2+json" \
| jq --raw-output '.layers[-1].digest'
)
View layer tarball:
curl http://localhost:5000/v2/hello-world-java/blobs/${DIGEST} \
--silent \
--header "Accept: application/vnd.docker.image.rootfs.diff.tar.gzip" \
| tar -tvz
Demo: Verifying a layer 020_advanced/030_layers
Verifying a layer digest:
curl http://localhost:5000/v2/hello-world-java/blobs/${DIGEST} \
--silent \
--header "Accept: application/vnd.docker.image.rootfs.diff.tar.gzip" \
| sha256sum
Calculating a layer’s length:
curl http://localhost:5000/v2/hello-world-java/blobs/${DIGEST} \
--silent \
--header "Accept: application/vnd.docker.image.rootfs.diff.tar.gzip" \
| wc -c
Registries
REST API and Image Manifest Specification v2.2
No UI
Manage images, layers, configurations
Upload, list, update, delete
Usage
Registries are accessed using HTTPS
Insecure registries must be defined expicitly
Accepted insecure registry: 127.0.0.1/8
Demo: Registries 020_advanced/030_layers
Tagging images remotely
Download existing manifest:
MANIFEST=$(
curl http://localhost:5000/v2/hello-world-java/manifests/latest \
--silent \
--header "Accept: application/vnd.docker.distribution.manifest.v2+json"
)
Upload manifest to new path:
curl http://localhost:5000/v2/hello-world-java/manifests/new \
--request PUT \
--header "Content-Type: application/vnd.docker.distribution.manifest.v2+json" \
--data "${MANIFEST}"