add make rules and docs for integ test esgz image

add rules to Makefile for converting image to esgz and pushing it to a
GHCR repository.
add documentation with examples for converting an image to esgz.

Signed-off-by: Gavin Inglis <[email protected]>

Author: ginglis13

Makefile

@@ -411,3 +411,17 @@ $(STARGZ_BIN): $(STARGZ_DIR)/go.mod tools/stargz-builder-stamp
 	--workdir /src/$(STARGZ_DIR) \
 	localhost/$(STARGZ_BUILDER_NAME):$(DOCKER_IMAGE_TAG) \
 	make
+
+##########################
+# eStargz formatted image 
+##########################
+CTR_REMOTE_BIN=$(STARGZ_DIR)/out/ctr-remote
+DEFAULT_BASE_IMAGE=public.ecr.aws/amazonlinux/amazonlinux:latest
+DEFAULT_ESGZ_IMAGE=ghcr.io/firecracker-microvm/firecracker-containerd/amazonlinux:latest-esgz
+.PHONY: esgz-test-image push-esgz-test-image
+esgz-test-image: stargz-snapshotter
+	$(CTR_REMOTE_BIN) image pull $(DEFAULT_BASE_IMAGE)
+	$(CTR_REMOTE_BIN) image optimize --oci $(DEFAULT_BASE_IMAGE) $(DEFAULT_ESGZ_IMAGE)
+
+push-esgz-test-image:
+	$(CTR_REMOTE_BIN) image push -u $(GH_USER):$(GH_PERSONAL_ACCESS_TOKEN) $(DEFAULT_ESGZ_IMAGE) $(DEFAULT_ESGZ_IMAGE)

snapshotter/demux/README.md

@@ -0,0 +1,49 @@
+# snapshotter
+
+## Building an esgz Formatted Image
+
+The demux snapshotter uses a publicly available [eStargz](https://github.com/containerd/stargz-snapshotter/blob/main/docs/estargz.md) formatted image in its integration testing pipeline. 
+This image has the reference `ghcr.io/firecracker-microvm/firecracker-containerd/amazonlinux:latest-esgz`. 
+
+### Optimize an Amazon Linux Container Image for esgz
+
+The `ctr-remote` binary is needed to optimize an image for the esgz image format. Building the stargz-snapshotter submodule provides `ctr-remote`, a `ctr` wrapper, in `_submodules/stargz-snapshotter/out/ctr-remote`.
+Refer to the [containerd stargz-snapshotter documentation on `ctr-remote`](https://github.com/containerd/stargz-snapshotter/blob/main/docs/ctr-remote.md) for additional details.
+
+The root level Makefile provides `make esgz-test-image` for pulling the latest Amazon Linux image locally and optimizing it for eStargz using `ctr-remote` into an image `ghcr.io/firecracker-microvm/firecracker-containerd/amazonlinux:latest-esgz`. 
+Code owners of `firecracker-containerd` then push the eStargz optimized image as this publicly available reference using `make push-esgz-test-image` with proper credential environment variables `GH_USER` and `GH_PERSONAL_ACCESS_TOKEN` set.
+
+### Example optimization and push to GHCR
+
+Using default base and esgz images:
+
+```bash
+$ make esgz-test-image
+$ GH_USER=xxx
+# set GH_PERSONAL_ACCESS_TOKEN with command substitution such that it does not show in shell history
+$ make \
+    GH_USER=$GH_USER \
+    GH_PERSONAL_ACCESS_TOKEN=`cat`
+    push-esgz-test-image
+# enter personal access token and CTRL^D
+```
+
+To pull, convert, and push to a repo where the user has permissions with custom base and esgz images:
+
+```bash
+$ DEFAULT_BASE_IMAGE=public.ecr.aws/amazonlinux/amazonlinux:2022
+$ DEFAULT_ESGZ_IMAGE=ghcr.io/$DESTINATION_REPO/amazonlinux:2022-esgz
+$ make \
+    DEFAULT_BASE_IMAGE=$DEFAULT_BASE_IMAGE \
+    DEFAULT_ESGZ_IMAGE=$DEFAULT_ESGZ_IMAGE \
+    esgz-test-image
+$ GH_USER=xxx
+# set GH_PERSONAL_ACCESS_TOKEN with command substitution such that it does not show in shell history
+$ make \
+    GH_USER=$GH_USER \
+    GH_PERSONAL_ACCESS_TOKEN=`cat`
+    DEFAULT_ESGZ_IMAGE=$DEFAULT_ESGZ_IMAGE \
+    push-esgz-test-image
+# enter personal access token and CTRL^D
+```
+