Pacemaker is an open source cluster resource manager software since 2004. IBM integrated Pacemaker with DB2 starting DB2 version 11.5.4.0. In version 11.5.4.0 Pacemaker was introduced as Technical Preview and then released for production use in 11.5.5.0. If you want to use open source Pacemaker cluster with DB2 you can use it but for Pacemaker cluster issues, you will not get support from IBM. Pacemaker can be used to automate failover in HADR env and setup mutual failover env.
Why to use DB2 Pacemaker: