Provide dynamic configuration file to Cassandra cluster

[PXMYH]

Intent is to use docker config create to create a docker configuration and provide it to Cassandra cluster running in Docker Swarm. Steps as follows:

docker config create cassandra.yaml ./res/cassandra.yaml
docker service create --replicas 1 --name cassandra_cluster --config source=cassandra.yaml,target=/etc/cassandra/cassandra.yaml,mode=644 -d cassandra:3.11.3

However, after feeding config to cluster, getting error:

[atlantis@kali cassandra]$ docker service logs cassandra_cluster
cassandra_cluster.1.scgjmt4g17kk@kali    | chown: changing ownership of '/etc/cassandra/cassandra.yaml': Read-only file system
cassandra_cluster.1.nr7entee1ahm@kali    | chown: changing ownership of '/etc/cassandra/cassandra.yaml': Read-only file system
cassandra_cluster.1.w1h0b6lwfd0s@kali    | chown: changing ownership of '/etc/cassandra/cassandra.yaml': Read-only file system
cassandra_cluster.1.qgjzujcwsokz@kali    | chown: changing ownership of '/etc/cassandra/cassandra.yaml': Read-only file system
[atlantis@kali cassandra]$ 

Reason being Cassandra locked permission to read only and docker config can't overwrite the file.

Possible solution:
instruct Cassandra instead of looking for config in default location /etc/cassandra, it can find config under /cassandra.yaml which is default docker config loading behavior

[PXMYH]

some Github issues:
kelseyhightower/consul-on-kubernetes#28
coreos/bugs#2384

[PXMYH]

--privileged=true maybe?