New findings. Here is my syslog in host machine.
Aug 7 16:23:20 raspberrypi dhcpcd[406]: veth2ee779b: adding default route
Aug 7 16:23:20 raspberrypi dhcpcd[406]: wlan0: deleting route to [192.168.1.0/24]
Aug 7 16:23:20 raspberrypi dhcpcd[406]: wlan0: deleting default route via [192.168.1.1]
Aug 7 16:23:20 raspberrypi dhcpcd[406]: eth0: received approval for [192.168.1.11]
Aug 7 16:23:20 raspberrypi dhcpcd[406]: eth0: adding route to [192.168.1.0/24]
Aug 7 16:23:20 raspberrypi dhcpcd[406]: eth0: adding default route via [192.168.1.1]
Aug 7 16:23:20 raspberrypi dhcpcd[406]: veth2ee779b: deleting default route
Aug 7 16:23:20 raspberrypi dhcpcd[406]: wlan0: received approval for [192.168.1.11]
Aug 7 16:23:20 raspberrypi dhcpcd[406]: wlan0: adding route to [192.168.1.0/24]
Aug 7 16:23:20 raspberrypi dhcpcd[406]: wlan0: adding default route via [192.168.1.1]
Aug 7 16:23:21 raspberrypi dhcpcd[406]: eth0: pid 406 deleted route to [192.168.1.0/24]
Aug 7 16:23:21 raspberrypi dhcpcd[406]: eth0: adding route to [192.168.1.0/24]
Aug 7 16:23:21 raspberrypi dhcpcd[406]: eth0: pid 406 deleted default route via [192.168.1.1]
Aug 7 16:23:21 raspberrypi dhcpcd[406]: wlan0: pid 406 deleted route to [192.168.1.0/24]
Aug 7 16:23:21 raspberrypi dhcpcd[406]: eth0: adding default route via [192.168.1.1])
Aug 7 16:23:21 raspberrypi dhcpcd[406]: wlan0: adding route to [192.168.1.0/24]
Aug 7 16:23:21 raspberrypi dhcpcd[406]: wlan0: pid 406 deleted default route via [192.168.1.1]
Aug 7 16:23:21 raspberrypi dhcpcd[406]: wlan0: adding default route via [192.168.1.1]
Aug 7 16:23:21 raspberrypi dhcpcd[406]: eth0: deleting route to [192.168.1.0/24]
Aug 7 16:23:21 raspberrypi dhcpcd[406]: eth0: deleting default route via [192.168.1.1]
Default route kept changing when docker container was running. Any comments on this?