Thanks 
We will test and hopefully report you.
We have tried to bring up MGM with QDB backend but it looks still MGM wants Sync daemon to be running. Since we are based on Docker container for EOS components (eos-docker), when a MGM with having two different MGM nodes (such as MGM1 and MGM2 for Master/Slave) in its configuration (/etc/xrd.cf.mgm) starts, it tries to bring up Sync via systemd - systemd is not installed in the base CentOS image - and then it fails.
I am quite confused that you told Sync is only used for in-memory namespace but it seems that it involves in HA configuration between MGM Master and Slave. Would you please have a look at the log below?
Thank you.
Best regards,
Sang-Un
++++++ (c) 2015 CERN/IT-DSS MgmOfs (meta data redirector) 4.5.8
=====> mgmofs enforces SSS authentication for XROOT clients
jemalloc is loaded!
jemalloc heap profiling is disabled
=====> mgmofs.hostname: eos-mgm-01.eoscluster.sdfarm.kr
=====> mgmofs.hostpref: eos-mgm-01
=====> mgmofs.managerid: eos-mgm-01.eoscluster.sdfarm.kr:1094
=====> mgmofs.fs: /
=====> mgmofs.targetport: 1095
=====> mgmofs.instance : eostestatcf
=====> mgmofs.metalog: /var/eos/md
=====> mgmofs.txdir: /var/eos/tx
=====> mgmofs.authdir: /var/eos/auth
=====> mgmofs.reportstorepath: /var/eos/report
=====> mgmofs.cfgtype: quarkdb
=====> mgmofs.fstgw: someproxy.cern.ch:3001
=====> mgmofs.nslib : /usr/lib64/libEosNsQuarkdb.so
=====> mgmofs.qdbcluster : eos-qdb-01.eoscluster.sdfarm.kr:7777 eos-qdb-02.eoscluster.sdfarm.kr:7777 eos-qdb-03.eoscluster.sdfarm.kr:7777
=====> mgmofs.redirector : false
=====> mgmofs.broker : root://eos-mgm.eoscluster.sdfarm.kr:1097//eos/eos-mgm-01.eoscluster.sdfarm.kr/mgm
=====> mgmofs.defaultreceiverqueue : /eos/*/fst
=====> mgmofs.fs: /
=====> mgmofs.errorlog : enabled
=====> all.role: manager
=====> setting message filter: Process,AddQuota,Update,UpdateHint,Deletion,PrintOut,SharedHash,work
=====> comment log in /var/log/eos/mgm/logbook.log
=====> eosxd stacktraces log in /var/log/eos/mgm/eosxd-stacktraces.log
=====> eosxd logtraces log in /var/log/eos/mgm/eosxd-logtraces.log
=====> mgmofs.alias: eos-mgm.eoscluster.sdfarm.kr
190920 01:20:13 time=1568942413.171078 func=Configure level=NOTE logid=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx unit=mgm@eos-mgm-01.eoscluster.sdfarm.kr:1094 tid=00007f530a1f28c0 source=XrdMgmOfsConfigure:1324 tident=<single-exec> sec= uid=0 gid=0 name= geo="" MGM_HOST=eos-mgm-01.eoscluster.sdfarm.kr MGM_PORT=1094 VERSION=4.5.8 RELEASE=20190910164416gitbb18f96 KEYTABADLER=136b2796 SYMKEY=Smb4JQeUdyJPQf+C+8w47in4j8g=
190920 01:20:13 time=1568942413.171219 func=set level=INFO logid=static.............................. unit=mgm@eos-mgm-01.eoscluster.sdfarm.kr:1094 tid=00007f530a1f28c0 source=InstanceName:39 tident= sec=(null) uid=99 gid=99 name=- geo="" Setting global instance name => eostestatcf
190920 01:20:13 time=1568942413.193492 func=Init level=INFO logid=cb9bce6e-db44-11e9-801a-0242864b7d17 unit=mgm@eos-mgm-01.eoscluster.sdfarm.kr:1094 tid=00007f530a1f28c0 source=Master:82 tident=<service> sec= uid=0 gid=0 name= geo="" systemd found on the machine = 0
190920 01:20:13 time=1568942413.324585 func=Init level=CRIT logid=cb9bce6e-db44-11e9-801a-0242864b7d17 unit=mgm@eos-mgm-01.eoscluster.sdfarm.kr:1094 tid=00007f530a1f28c0 source=Master:178 tident=<service> sec= uid=0 gid=0 name= geo="" failed to start sync service
190920 01:20:13 251 XrootdConfig: Unable to create file system object via libXrdEosMgm.so
190920 01:20:13 251 XrootdConfig: Unable to load file system.
------ xrootd protocol initialization failed.
190920 01:20:13 251 XrdProtocol: Protocol xrootd could not be loaded
190920 01:20:13 251 XrdConfig: Unable to create home directory //mgm; permission denied
------ xrootd mgm@eos-mgm-01.eoscluster.sdfarm.kr:-1 initialization failed.