Write more env vars to lib file and give a better description of why we source the lib file

Author: triarius

packer/linux/conf/bin/bk-configure-docker.sh

@@ -26,9 +26,12 @@ trap '[[ $? = 0 ]] && on_exit' EXIT
 exec > >(tee -a /var/log/elastic-stack.log | logger -t user-data -s 2>/dev/console) 2>&1
 
 
-echo Reading variables from AMI creation...
+echo Sourcing /usr/local/lib/bk-configure-docker.sh...
+echo This file is written by the scripts in packer/scripts.
+echo Note that the path is /usr/local/lib, not /usr/local/bin.
+echo Contents of /usr/local/lib/bk-configure-docker.sh:
 # shellcheck disable=SC1091
-source /usr/local/lib/bk-configure-docker.sh
+tee /dev/stderr < /usr/local/lib/bk-configure-docker.sh | source /dev/stdin
 
 if [[ "${DOCKER_USERNS_REMAP:-false}" == "true" ]]; then
   echo Configuring user namespace remapping...

packer/linux/scripts/install-docker.sh

@@ -47,11 +47,22 @@ sudo cp /tmp/conf/bin/docker-compose /usr/local/bin/docker-compose
 sudo chmod +x /usr/local/bin/docker-compose
 docker-compose version
 
+# Writing QEMU container version info to /usr/local/lib/bk-configure-docker.sh.
+# We only pull this image when we build the AMI. It will be run in
+# /usr/local/bin/bk-configure-docker.sh, but it needs to know the image digest
+# to make sure it does not pull in another image instead.
+# NOTE: the executable file is in /usr/local/bin and it sources as file of the
+# same name in /usr/local/lib. These are not the same file.
 # See https://docs.docker.com/build/building/multi-platform/
+
+echo Contents of /usr/local/lib/bk-configure-docker.sh:
+cat <<'EOF' | sudo tee -a /usr/local/lib/bk-configure-docker.sh
 QEMU_BINFMT_VERSION=7.0.0-28
 QEMU_BINFMT_DIGEST=sha256:66e11bea77a5ea9d6f0fe79b57cd2b189b5d15b93a2bdb925be22949232e4e55
 QEMU_BINFMT_TAG="qemu-v${QEMU_BINFMT_VERSION}@${QEMU_BINFMT_DIGEST}"
+EOF
+# shellcheck disable=SC1091
+source /usr/local/lib/bk-configure-docker.sh
 sudo mkdir -p /usr/local/lib
-echo "QEMU_BINFMT_TAG=\"$QEMU_BINFMT_TAG\"" | sudo tee -a /usr/local/lib/bk-configure-docker.sh
 echo Pulling qemu binfmt for multiarch...
 sudo docker pull "tonistiigi/binfmt:${QEMU_BINFMT_TAG}"