Modify j2 template files in docker-dhcp-relay. Add dhcprelayd to group dhcp-relay instead of isc-dhcp-relay-VlanXXX, which would make dhcprelayd to become critical process.
In dhcprelayd, subscribe FEATURE table to check whether dhcp_server feature is enabled.
2.1 If dhcp_server feature is disabled, means we need original dhcp_relay functionality, dhcprelayd would do nothing. Because dhcrelay/dhcpmon configuration is generated in supervisord configuration, they will automatically run.
2.2 If dhcp_server feature is enabled, dhcprelayd will stop dhcpmon/dhcrelay processes started by supervisord and subscribe dhcp_server related tables in config_db to start dhcpmon/dhcrelay processes.
2.3 While dhcprelayd running, it will regularly check feature status (by default per 5s) and would encounter below 4 state change about dhcp_server feature:
A) disabled -> enabled
In this scenario, dhcprelayd will subscribe dhcp_server related tables and stop dhcpmon/dhcrelay processes started by supervisord and start new pair of dhcpmon/dhcrelay processes. After this, dhcpmon/dhcrelay processes are totally managed by dhcprelayd.
B) enabled -> enabled
In this scenaro, dhcprelayd will monitor db changes in dhcp_server related tables to determine whether to restart dhcpmon/dhrelay processes.
C) enabled -> disabled
In this scenario, dhcprelayd would unsubscribe dhcp_server related tables and kill dhcpmon/dhcrelay processes started by itself. And then dhcprelayd will start dhcpmon/dhcrelay processes via supervisorctl.
D) disabled -> disabled
dhcprelayd will check whether dhcrelay processes running status consistent with supervisord configuration file. If they are not consistent, dhcprelayd will kill itself, then dhcp_relay container will stop because dhcprelayd is critical process.
Why I did it
Currently SONiC use the 'isc-dhcp-relay' package to allow DHCP relay functionality on IPv4 networks only.
This will allow the IPv6 functionality along the IPv4 type.
How I did it
Edit supervisord template to start DHCPv6 instances when configured to do so on Config DB.
Align cfg unit test to the new change.
Add DHCPv6 relay minigraph parsing support and a suitable t0 topology xml file for UT.
How to verify it
Configure DHCPv6 agents as described on the feature HLD: Azure/SONiC#765
Test it with real client/server with IPv6 or use the dedicated automatic test: Azure/sonic-mgmt#3565
Signed-off-by: Shlomi Bitton <shlomibi@nvidia.com>
* Split docker-dhcp-relay.supervisord.conf.j2 template into several files for easier code maintenance
