keepalived -v

Keepalived v2.0.6 (02/03,2019), git commit +

Copyright(C) 2001-2019 Alexandre Cassen, [email protected]

Built with kernel headers for Linux 4.19.25
Running on Linux 4.19.25-vhulk1902.3.1.h113.aarch64 #1 SMP Tue Feb 12 00:00:00 UTC 2019

configure options:

Config options: LVS VRRP VRRP_AUTH OLD_CHKSUM_COMPAT FIB_ROUTING

System options: PIPE2 SIGNALFD INOTIFY_INIT1 VSYSLOG IPV4_DEVCONF LIBNL3 RTA_ENCAP RTA_EXPIRES RTA_NEWDST RTA_PREF FRA_SUPPRESS_PREFIXLEN FRA_SUPPRESS_IFGROUP FRA_TUN_ID RTAX_CC_ALGO RTAX_QUICKACK RTEXT_FILTER_SKIP_STATS FRA_L3MDEV FRA_UID_RANGE RTAX_FASTOPEN_NO_COOKIE RTA_VIA FRA_OIFNAME FRA_PROTOCOL FRA_IP_PROTO FRA_SPORT_RANGE FRA_DPORT_RANGE IFA_FLAGS IP_MULTICAST_ALL LWTUNNEL_ENCAP_MPLS LWTUNNEL_ENCAP_ILA LIBIPTC_LINUX_NET_IF_H_COLLISION LIBIPVS_NETLINK IPVS_DEST_ATTR_ADDR_FAMILY IPVS_SYNCD_ATTRIBUTES IPVS_64BIT_STATS VRRP_VMAC SOCK_NONBLOCK SOCK_CLOEXEC O_PATH GLOB_BRACE INET6_ADDR_GEN_MODE SO_MARK SCHED_RT SCHED_RESET_ON_FORK

old config:

! Configuration File for keepalived
  
virtual_server 22.22.91.58 5001 {
    delay_loop 6
    lb_algo rr
    lb_kind DR
    protocol TCP
    alpha

    real_server 9.82.250.109 5001 {
        weight 1
        TCP_CHECK {
            connect_port 23
            connect_timeout 15
            retry 3
            delay_before_retry 3
        }
    }
}

new config:

! Configuration File for keepalived
  
virtual_server 22.22.91.58 5001 {
    delay_loop 6
    lb_algo rr
    lb_kind DR
    protocol TCP
    alpha

    real_server 9.82.250.109 5001 {
        weight 1
        TCP_CHECK {
            connect_port 22
            connect_timeout 15
            retry 3
            delay_before_retry 3
        }
    }
}

step 1: start keepalived with old config, 23 port is unreachable
step 2: just for a while and then modify the config to the new one and reload
step 3: observe the log and you will see the success log but lack of Adding service [9.82.250.109]:tcp:5001 to VS [22.22.91.58]:tcp:5001

the reason is the new checker's state is is_up, so it can not update it's state properly