While running a Sandfly start script (e.g. start_sandfly.sh, start_node.sh, etc), we have become aware of an occurrence where you may receive an error message similar to this: 

docker: Error response from daemon: driver failed programming external connectivity on endpoint sandfly-rabbit (bd09d052236de4e14c9b279dec65b8c627aeae70715b6a625f545d4530ae772c): Error starting userland proxy: listen tcp4 0.0.0.0:5673: bind: address already in use.

This is a docker-specific matter that currently seems to not be fully resolved. In the mean time, should you encounter this error, the information contained within this docker-proxy bug ticket has been found to be helpful:

https://github.com/moby/moby/issues/25981

As this is a rare and not reproduceable case, we welcome any other input or information regarding this topic.