Default checkpoint location problematic when using docker 
The default behavior of ModelCheckpoint is to use os.getcwd(). Outside my docker container, this ended up being the same directory where my tensorboard logs were saved (e.g. /my/dir/tb_logs/default/version_0/checkpoints/).  But inside the docker container, it saved to the internal working directory (e.g. /home/default/version_0/checkpoints/). Since this location disappeared along with the container, the checkpoint was gone, and there was no warning raised to explain why.
Requiring a checkpoint directory isn't desirable, but I'd like to help others avoid this grief in the future. Is there a better way to infer a default location than os.getcwd()? Something as simple as a print statement with the checkpoint location would have saved me a lot of time troubleshooting.