veth interface for containers on RouterOS

add IP to DNS server

/ip dns static
add address=10.100.10.200 name=haproxy.auriel.local

reserve IP in DHCP server

/ip dhcp-server lease
add address=10.100.10.200 comment="HA-proxy container veth" dhcp-option=domain-search mac-address=00:00:00:00:00:01 server=dhcpserver_INTER

create the interface

/interface/veth
add name=veth-haproxy address=10.100.10.200/24 gateway=10.100.10.254

add the interface to the bridge

/interface bridge port
add bridge=bridge1 interface=veth-haproxy disabled=no hw=no pvid=10

And add as untagged to VLAN 10:

/interface/bridge/vlan
edit number=0 untagged

Add veth-haproxy to the list ans save with CRTL-o.