Warning: External references from destroy provisioners are deprecated

[ximon18]

Warning: External references from destroy provisioners are deprecated

  on ../lib/docker/main.tf line 99, in resource "null_resource" "setup_docker":
  99:     environment = merge(local.docker_env_vars, local.krill_env_vars)

Destroy-time provisioners and their connection configurations may only
reference attributes of the related resource, via 'self', 'count.index', or
'each.key'.

References to other resources during the destroy phase can cause dependency
cycles and interact poorly with create_before_destroy.

(and 4 more similar warnings elsewhere)

Caused by this fragment from the Terraform 0.12.18 release notes:

Inside provisioner blocks that have when = destroy set, and inside any connection blocks that are used by such provisioner blocks, it is now deprecated to refer to any objects other than self, count, and each.