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Docker manifests: Usability across multiple architectures

While doing a cross platform framework for orchestration targeting both ARM and AMD64 devices, I have been using a functionality called docker manifests.

This allows you to have multiple images in one docker tag.

It’s currently an experimental feature right now so needs to be enabled.

Configuring Docker

Can be done by doing the following entry to your ~/.docker/config.json file

"experimental": "enabled"

Also it requires you to have an available image for each architecture so that you can annote it to the manifest.

Sample config file

Here is a sample of what the configuration should look like

{
    "auths": {
        "https://index.docker.io/v1/": {
        "auth": "Your-Authorization-Key-Here"
        }
    },
    "HttpHeaders": {
    "User-Agent": "Docker-Client/18.09.5 (linux)"
    },
    "experimental": "enabled"
}

Set up Manifests

Next step is to build, tag, and push the builds on each platform to docker hub.

Be prepared to name them by architecture so you can reference them later.

Lets create the manifest

Now we have all the names for each tags do the following command

docker -D manifest create username/repo:tagwithmanifest  username/repo:archtag1 username/repo:archtag2 username/repo:archtag3

Now we annote each manifest

We need to now add an annotation to each manifest. By default it is linux amd64 (assuming you used a 64bit linux device).

In the below example I am adding metadata to archtag2 and archtag3 with the appropriate architectures.

docker manifest annotate  username/repo:tagwithmanifest username/repo:archtag2  --os linux  --arch arm  --variant v6
docker manifest annotate  username/repo:tagwithmanifest username/repo:archtag3  --os linux  --arch arm  --variant v7

Checking the changes

Finally Check that the changes have been applied

docker manifest inspect username/repo:tagwithmanifest

Example of inspect file

An example should look like this

{
   "schemaVersion": 2,
   "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
   "manifests": [
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 950,
         "digest": "sha256:6b1c68ef1540a6d1fdeb75a48c192d6a3905f63920513b3715e474f74e630d9d",
         "platform": {
            "architecture": "amd64",
            "os": "linux"
         }
      },
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 950,
         "digest": "sha256:f55c26d0ffac307d569c055588268e27898d877a152f8f295feaa76004a94d16",
         "platform": {
            "architecture": "arm",
            "os": "linux",
            "variant": "v7"
         }
      }
   ]
}

Pushing your Manifest to dockerhub

If everything is good, you may push the manifest to dockerhub

docker manifest push username/repo:tagwithmanifest

Testing out your docker hub changes

First of all wipe down all the images using the docker images command. Then execute docker rmi against all the images.

Next pull the docker image from docker hub on each environment

docker pull username/repo:tagwithmanifest

After you have fetched the tag, you can furthermore try to run it but if it fetchable it should already work.

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Who am I?

I write codes, work on projects when inspiration strikes, I am passionate about usability / user interaction, I love new technology (right now blockchain), I travel, and I blog (ocassionally, but try to be regular)