ARG commands - clustering

Hello,

I have been trying to enable clustering through compose file with no joy.

Could someone shed some light to the secret sauce?

splunkmaster:
   restart: always
   build: ./splunkmaster
   hostname: splunkmaster
   # image: splunk/splunk:6.5.3
   environment:
     SPLUNK_START_ARGS: --accept-license --answer-yes
     SPLUNK_ENABLE_LISTEN: 9997
     SPLUNK_CMD_1: splunk edit cluster-config -mode master -replication_factor 3 -search_factor 2 -secret newsecret123456 -cluster_label cluster1 auth admin:changeme
     SPLUNK_CMD_2: splunk restart