docs: local image registry for oci containers

docs/guide/application_container.md

@@ -31,4 +31,101 @@ $ sudo -i
 ## Sulu application container
 An example makefile to generate sulu application container tar ball can be accessed [here](https://dev.iopsys.eu/iopsys/swmodd/-/blob/devel/examples/sulu/README.md)
 
+## Local application containers with multi-arch support
+It is possible to create an multi-arch oci container and store it in Gitlab image registry, to support variety of devices and platforms.
+
+This can be done in many ways, but in this example I am using docker buildx to build multi-arch containers.
+
+### Pre-setup
+
+1. Create a access-token with read/write access to image registry in gitlab
+2. Install buildx
+
+```bash
+export BUILDX_VERSION="v0.10.4"
+export BUILDX_ARCH="linux-amd64"
+wget -O /usr/bin/docker-buildx https://github.com/docker/buildx/releases/download/${BUILDX_VERSION}/buildx-${BUILDX_VERSION}.${BUILDX_ARCH}
+```
+
+### Build
+To build a multi-arch oci container and push to Gitlab image registry, run following commands, sulu example container used in this example:
+
+```bash
+$ docker-buildx create --use
+$ cd examples/sulu
+$ make extract
+$ docker-buildx build --provenance=false --platform linux/386,linux/amd64,linux/arm/v6,linux/arm/v7,linux/arm64/v8 --tag dev.iopsys.eu:5050/lcm/swmodd/sulu:v2.1.2 --push .
+```
+
+Above commands creates sulu multi-arch containers and push it to Gitlab [image registry](https://dev.iopsys.eu/lcm/swmodd/container_registry/).
+
+### Verify
+Image details can be verified with docker manifest command:
+
+```bash
+vdutta@SW019:~$ docker manifest inspect dev.iopsys.eu:5050/lcm/swmodd/sulu
+{
+   "schemaVersion": 2,
+   "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
+   "manifests": [
+      {
+         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
+         "size": 1871,
+         "digest": "sha256:5d362624ae3d27ecea7486a6b8f6a103b7d52543574baa483dd9034402727eb5",
+         "platform": {
+            "architecture": "386",
+            "os": "linux"
+         }
+      },
+      {
+         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
+         "size": 1871,
+         "digest": "sha256:db776d064d0763874bca5f8c4a5f396e339a901350cbcc8714c5e19c3adcefc9",
+         "platform": {
+            "architecture": "amd64",
+            "os": "linux"
+         }
+      },
+      {
+         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
+         "size": 1871,
+         "digest": "sha256:0323e482ca40f631a46993736b65459554149ac1586f04042cf61e738236bc64",
+         "platform": {
+            "architecture": "arm",
+            "os": "linux",
+            "variant": "v5"
+         }
+      },
+      {
+         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
+         "size": 1871,
+         "digest": "sha256:63d6bcea175828b4a8034b874948e774e40eea8f71657c6e0d7a4d5881662db8",
+         "platform": {
+            "architecture": "arm",
+            "os": "linux",
+            "variant": "v6"
+         }
+      },
+      {
+         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
+         "size": 1871,
+         "digest": "sha256:29152f374de66400c489413c2fcddfd26b8edad4c048efea57b0c17f07aa05ed",
+         "platform": {
+            "architecture": "arm",
+            "os": "linux",
+            "variant": "v7"
+         }
+      }
+   ]
+}
+vdutta@SW019:~$
+```
+
+Above output provides the sha1 hash per architechture, to use a specific image in device, it can be used with its sha checksum hash, like below
+
+```bash
+obuspa -c operate "Device.SoftwareModules.InstallDU(URL=docker://dev.iopsys.eu:5050/lcm/swmodd/sulu@sha256:0323e482ca40f631a46993736b65459554149ac1586f04042cf61e738236bc64)"
+```
+
+This installs sulu for arm/v5 arch.