upgrade to docker 20.10.21

provision/provision-docker.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 set -euxo pipefail
 
-docker_version="${1:-20.10.16}"; shift || true
+docker_version="${1:-20.10.21}"; shift || true
 registry_proxy_domain="${1:-$(hostname --fqdn)}"; shift || true
 # NB as-of docker 19.03.8, there is still no way to specify a registry mirror credentials,
 #    as such, we cannot use our docker-group registry, instead we must use the docker-proxy