Copy files between containers

Hello
We have a requirement to save file to a volume of a container (container-b) from another container(container-a). Currently, both the containers on the same host, I see these options
1 sftp - have a ftp server running on container-b

2 have a common volume for both container-a and container-b - this could be an issue if there is a distributed deployment in future

3 DockerClient.copyToContainer() from container-a to container-b assuming both containers are on the same host - again an issue if there is a distributed deployment in future

Currently, the best option is see is to use option #1. Sorry, this might seem like an asking-for-opinion kind of a question but want to know if there are any issue you see with the way i am approaching or have better options for this requirement