oras-helm-demo

Demo of using oras as a Go library to push/pull a Helm chart to/from a registry.

Setup

Start a Distribution registry server at localhost:5000 with the following command:

docker run -dp 5000:5000 --restart=always --name registry registry:2

The will run in the background. Use docker logs -f registry to see the logs and docker rm -f registry to stop.

Examples

To run examples below, clone this repo and gather required dependencies (requires Go 1.11+):

git clone git@github.com:jdolitsky/oras-helm-demo.git && cd oras-helm-demo/
GO111MODULE=on go mod vendor

Push Helm chart to registry

Souce code for push.go can be found here.

Run push.go with 2 arguments:

go run push.go mychart/ localhost:5000/mychart:latest

The first arg, mychart/, refers to a Helm chart directory path.

The second arg, localhost:5000/mychart:latest is a reference to a remote registry address.

This will push the chart as 2 separate layers with the following media types:

1. application/vnd.cncf.helm.chart.meta.v1+json (metadata)
2. application/vnd.cncf.helm.chart.content.v1+tar (package content)

By separating Chart.yaml (a.k.a the metadata) from the rest of the Helm chart, we prevent storing the same content in the registry twice for different names.

Pull Helm chart from registry

Souce code for pull.go can be found here.

Run pull.go with a single argument:

go run pull.go localhost:5000/mychart:latest

This will download and convert the stored Helm chart into a usable format, saving it to ./output/<chartname>.

The Manifest

You can use curl and jq to inspect the manifest of a Helm chart stored in a registry:

curl -s -H 'Accept: application/vnd.oci.image.manifest.v1+json' \
    http://localhost:5000/v2/mychart/manifests/latest | jq

Example manifest:

{
  "schemaVersion": 2,
  "config": {
    "mediaType": "application/vnd.oci.image.config.v1+json",
    "digest": "sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a",
    "size": 2
  },
  "layers": [
    {
      "mediaType": "application/vnd.cncf.helm.chart.meta.v1+json",
      "digest": "sha256:c356ec641a696eb5f3320bed9e8ceeb505fcc84b7ee072a85a8098fc362e13b7",
      "size": 210,
      "annotations": {
        "org.opencontainers.image.title": "meta.json"
      }
    },
    {
      "mediaType": "application/vnd.cncf.helm.chart.content.v1+tar",
      "digest": "sha256:e5e50410addbc4d1aa16100e42e4eb99f2bb4b04157de130a528e6e5d8c71774",
      "size": 431,
      "annotations": {
        "chart.name": "mychart",
        "chart.version": "2.7.1",
        "org.opencontainers.image.title": "content.tgz"
      }
    }
  ]
}