I ran into this same issue and it turned out to be the selinux was set to enforcing, and that prevented the file system writes.

The file /config/prometheus/isc_tmp_yml_file.yml seems to be a temp file that is used during the creation of a new cluster.  However, with selinux enforcing, it may be that there would be other file write issues.

To verify the issue was selinux, I used "docker exec -it <container> bash" to connect to bash on the iris container that start.sh started.  Once there I used "touch /config/prometheus/isc_tmp_yml_file.yml" to attempt to create the file and it failed.

I then exited bash and used setenforce 0 to temporarily change selinux from enforcing to premissive and retried the touch and it was successful.  At that point I was able to continue with the creation of a cluster in SAM.

I have not looked into what policies would need to be created to enable SAM to run with selinux enforcing, but that will be necessary before deploying into production unless the cluster can operate without issue after configuration, in which case, perhaps configuration can be done with selinux set to permissive and then returned to enforcing for operations.