At first set up three nodes, for example using docker:

sudo docker run -ti --name odl1 opendaylight/odl

and so on. Then at first use the ./bin/configure_cluster.sh script with the proper ip's to create a cluster and then start ODL on each node with ./bin/start and open a karaf shell later on doing ./bin/client.

At the shell do the following:

feature:install odl-restconf-all odl-l2switch-all odl-dlux-core

Then try to connect with Mininet to the controller after some time and this should work:

sudo mn --controller=remote,ip=172.17.0.2 --topo=linear,2 --switch=ovsk

However, unlike in the single controller case pingall will fail. As nodes are visible in the dlux interface, the problem must be that there aren't any flows being installed.

Link to related email-thread: https://lists.opendaylight.org/pipermail/opendaylight-users/2017-April/000750.html