By default clustering is disabled, however when a freshly installed instance starts up, it tries to discover potential clustering partners via multicast none the less. This is evident with Ubuntu when "ufw" is active, which blocks multicast by default:
May 12 23:11:46 pheme kernel: [549586.656109] [UFW BLOCK] IN=eth1 OUT= MAC=01:00:5e:00:00:01:fe:54:00:24:07:4d:08:00 SRC=0.0.0.0 DST=188.8.131.52 LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 DF PROTO=2
May 12 23:11:46 pheme kernel: [549586.656131] [UFW BLOCK] IN=eth0 OUT= MAC=01:00:5e:00:00:01:00:24:21:ef:35:90:08:00 SRC=0.0.0.0 DST=184.108.40.206 LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 DF PROTO=2
When clustering is disabled, as it is by default, we should not try to do any kind of discovery either.