Hello,
with regard to the external etcd, it looks like you’ve hitting a deficiency in the wrapper script logic used in the docker image to deal with the init.
The script currently uses SENSU_HOSTNAME
for the for the init wait loop, which is probably inappropriate for the external etcd service in your configuration. You’ll probably need a custom docker image until we can get this sorted out in the official images.
Here’s a post from earlier this month where I walk through how I make custom changes to the entrypoint. Hopeful this will get you unstuck for now.