Add soci standalone convert docs

Signed-off-by: Praful Gupta <prafulgupta6@gmail.com>

Author: prafgup

docs/cli-usage.md

@@ -54,7 +54,7 @@ This command creates a new SOCI-enabled image that packages the original image a
 > [!NOTE]
 > SOCI Index Manifest v2 is the recommended approach for production deployments as it provides immutable binding between the image and SOCI index, preventing runtime behavior changes.
 
-Usage: ```soci convert [flags] <source_image_ref> <dest_image_ref> ```
+Usage: ```soci convert [flags] <source> <dest> ```
 
 Flags:
 
@@ -64,6 +64,8 @@ Flags:
    - `xattr` :  When true, adds DisableXAttrs annotation to SOCI index. This annotation often helps performance at pull time.
  - ```--all-platforms``` : Convert all platforms of a multi-platform image
  - ```--platform``` : Convert only the specified platform (e.g., linux/amd64)
+ - ```--standalone``` : Run in standalone mode without a containerd runtime. Reads an OCI image layout (tar or directory) from disk and writes a converted OCI image layout without requiring a running containerd instance. See [Standalone mode](#standalone-mode) below.
+ - ```--format``` : Output format for standalone mode: ```oci-archive``` (tar, default) or ```oci-dir``` (directory). Only used with ```--standalone```.
 
 **Example:**
 ```
@@ -75,6 +77,31 @@ soci convert public.ecr.aws/soci-workshop-examples/ffmpeg:latest public.ecr.aws/
 soci convert --all-platforms public.ecr.aws/soci-workshop-examples/ffmpeg:latest public.ecr.aws/soci-workshop-examples/ffmpeg:latest-soci
 ```
 
+#### Standalone mode
+
+Standalone mode enables SOCI conversion without a running containerd daemon. This is useful in CI/CD pipelines and other environments where containerd is unavailable or running it would require privileged access.
+
+In standalone mode, ```<source>``` and ```<dest>``` are file paths (not image references). The source can be an OCI image layout tar archive or directory. The output format is controlled by the ```--format``` flag.
+
+Standalone mode does not require containerd, sudo, or any other daemon. You can use tools like [skopeo](https://github.com/containers/skopeo) or [crane](https://github.com/google/go-containerregistry/blob/main/cmd/crane) to download and push images.
+
+> [!NOTE]
+> The input tar or directory must be in **OCI image layout** format. Docker-style tarballs (e.g., from `docker save` or `crane pull` without `--format oci`) are not compatible.
+
+**Tar output format workflow** (using skopeo):
+```shell
+skopeo copy docker://public.ecr.aws/soci-workshop-examples/ffmpeg:latest oci-archive:ffmpeg.tar
+soci convert --standalone ffmpeg.tar ffmpeg-soci.tar
+skopeo copy oci-archive:ffmpeg-soci.tar docker://public.ecr.aws/soci-workshop-examples/ffmpeg:latest-soci
+```
+
+**Directory output format workflow** (using skopeo):
+```shell
+skopeo copy docker://public.ecr.aws/soci-workshop-examples/ffmpeg:latest oci:ffmpeg-oci
+soci convert --standalone --format oci-dir ffmpeg-oci ffmpeg-soci-oci
+skopeo copy oci:ffmpeg-soci-oci docker://public.ecr.aws/soci-workshop-examples/ffmpeg:latest-soci
+```
+
 ### soci push
 Push SOCI artifacts to a registry by image reference (SOCI Index Manifest v1 only)
 

docs/getting-started.md

@@ -102,6 +102,9 @@ sudo soci convert docker.io/library/rabbitmq:latest $REGISTRY/rabbitmq:latest
 sudo nerdctl push $REGISTRY/rabbitmq:latest
 ```
 
+> **Note**
+> If containerd is not available (e.g., in CI/CD pipelines), you can use `soci convert --standalone` to convert OCI image layouts on disk without a running containerd instance. See the [CLI usage documentation](./cli-usage.md#standalone-mode) for details.
+
 After this step, please check your registry to confirm the image and SOCI index are present.
 You can go to your registry console or use your registry's CLI (e.g. for ECR, you
 can use `aws ecr describe-images --repository-name rabbitmq --region $AWS_REGION`).

docs/soci-index-manifest-v2.md

@@ -38,6 +38,9 @@ sudo nerdctl pull --snapshotter soci \
 
 See [the getting started guide](./getting-started.md) for more information.
 
+> **Note**
+> If containerd is not available (e.g., in CI/CD pipelines), you can use `soci convert --standalone` to convert OCI image layouts on disk without a running containerd instance. See the [CLI usage documentation](./cli-usage.md#standalone-mode) for details.
+
 ## Continuing to Use SOCI Index Manifest v1
 
 There are some use-cases where the dynamic nature of SOCI Index Manifest v1 adds significant value. For those users, SOCI Index Manifest v1 is still available in the SOCI snapshotter; however, it is disabled by default. By re-enabling it, you should be aware that adding a SOCI index to an existing image can change the runtime characteristics of the image. We strongly recommend that you migrate to SOCI-enabled images and SOCI Index Manifest V2 which immutably binds a SOCI index to a new image and allows you to manage changes to your production workloads through deployments, just like you would for any other change.