Requests send with uac module's functions like uac_req_send() and remote registrations use the TM module, but don't actually do (DNS) failover when a destination is unreachable or sends a 503.

In the tm's uac.c, t_uac_prepare() function, i can already see that the dns handle is stored in a throwaway variable instead of in the transaction, but fixing the issue isn't as simple as just storing it in the transaction (print_uac_request_from_buf() needs a uas in the transaction).

Due to github not supporting attachments to issues, the sample config and debug log are inline.... :(

$ host -t SRV _sip._udp.failover.test.speakup.nl _sip._udp.failover.test.speakup.nl has SRV record 10 0 1111 try1.test.speakup.nl. _sip._udp.failover.test.speakup.nl has SRV record 100 0 2222 try2.test.speakup.nl.

Jun 15 10:00:03 rio UACFailover[18178]: INFO: <script>: Sending OPTIONS request to sip:failover.test.speakup.nl Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: tm [uac.c:249]: t_uac_prepare(): DEBUG:tm:t_uac: next_hop=<sip:failover.test.speakup.nl> Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [dns_cache.c:537]: _dns_hash_find(): (_sip._udp.failover.test.speakup.nl(34), 33), h=825 Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [resolve.c:937]: get_record(): skipping 8 NS (p=0x9ea284, end=0x9ea3e9) Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [resolve.c:952]: get_record(): parsing 9 ARs (p=0x9ea335, end=0x9ea3e9) Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [dns_cache.c:1741]: dns_get_related(): (0x7f225233eb38 (_sip._udp.failover.test.speakup.nl, 33), 33, *0x7f2257baf2b8) (0) Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [dns_cache.c:840]: dns_cache_add_unsafe(): adding _sip._udp.failover.test.speakup.nl(34) 33 (flags=0) at 825 Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [dns_cache.c:840]: dns_cache_add_unsafe(): adding try1.test.speakup.nl(20) 1 (flags=0) at 310 Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [dns_cache.c:840]: dns_cache_add_unsafe(): adding try2.test.speakup.nl(20) 1 (flags=0) at 307 Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [dns_cache.c:2336]: dns_srv_get_nxt_rr(): (0x7f225233eb38, 0, 0, 1597643831): selected 0/1 in grp. 0 (rand_w=0, rr=0x7f225233eba0 rd=0x7f225233ebb8 p=10 w=0 rsum=0) Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [dns_cache.c:537]: _dns_hash_find(): (try1.test.speakup.nl(20), 1), h=310 Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [dns_cache.c:2926]: dns_a_resolve(): (try1.test.speakup.nl, 0) returning 0 Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [dns_cache.c:3169]: dns_srv_resolve_ip(): ("_sip._udp.failover.test.speakup.nl", 0, 0), ret=0, ip=192.168.1.245 Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [dns_cache.c:3260]: dns_srv_sip_resolve(): (failover.test.speakup.nl, 0, 0), srv0, ret=0 Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: tm [uac.c:150]: dlg2hash(): DEBUG: dlg2hash: 54501 Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: tm [uac.c:351]: t_uac_prepare(): executing event_route[tm:local-request] Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [parser/msg_parser.c:606]: parse_msg(): SIP Request: Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [parser/msg_parser.c:608]: parse_msg(): method: <OPTIONS> Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [parser/msg_parser.c:610]: parse_msg(): uri: <sip:failover.test.speakup.nl> Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [parser/msg_parser.c:612]: parse_msg(): version: <SIP/2.0> Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [parser/parse_via.c:1254]: parse_via_param(): Found param type 232, <branch> = <z9hG4bK5e4d.47adbbf5000000000000000000000000.0>; state=16 Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [parser/parse_via.c:2642]: parse_via(): end of header reached, state=5 Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [parser/msg_parser.c:496]: parse_headers(): parse_headers: Via found, flags=2 Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [parser/msg_parser.c:498]: parse_headers(): parse_headers: this is the first via Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [parser/parse_addr_spec.c:894]: parse_addr_spec(): end of header reached, state=10 Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [parser/msg_parser.c:173]: get_hdr_field(): DEBUG: get_hdr_field: <To> [22]; uri=[sip:to.example.com] Jun 15 10:00:03 rio UACFailover[18178]: [97B blob data] Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [parser/msg_parser.c:153]: get_hdr_field(): get_hdr_field: cseq <CSeq>: <10> <OPTIONS> Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: pv [pv_core.c:376]: pv_get_xto_attr(): no Tag parameter Jun 15 10:00:03 rio UACFailover[18178]: INFO: <script>: [udp:172.28.4.128:6789] [10 OPTIONS] Request (cid: 6cd531e47cc63e20-18178@172.28.4.128 Branch: -1 ToTag: <null> len:382) To <sip:failover.test.speakup.nl> via <sip:failover.test.speakup.nl> Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [usr_avp.c:631]: destroy_avp_list(): destroying list (nil) Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [usr_avp.c:631]: destroy_avp_list(): destroying list (nil) Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [usr_avp.c:631]: destroy_avp_list(): destroying list (nil) Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [usr_avp.c:631]: destroy_avp_list(): destroying list (nil) Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [usr_avp.c:631]: destroy_avp_list(): destroying list (nil) Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [usr_avp.c:631]: destroy_avp_list(): destroying list (nil) Jun 15 10:00:03 rio UACFailover[18178]: DEBUG: <core> [xavp.c:446]: xavp_destroy_list(): destroying xavp list (nil) Jun 15 10:00:05 rio UACFailover[18176]: DEBUG: tm [t_reply.c:1230]: t_should_relay_response(): ->>>>>>>>> T_code=0, new_code=408 Jun 15 10:00:05 rio UACFailover[18176]: WARNING: tm [t_reply.c:957]: run_failure_handlers(): Warning: run_failure_handlers: no UAC support (1, 0) Jun 15 10:00:05 rio UACFailover[18176]: DEBUG: tm [t_reply.c:2016]: local_reply(): DEBUG: local_reply: branch=0, save=0, winner=0 Jun 15 10:00:05 rio UACFailover[18176]: DEBUG: tm [t_reply.c:2053]: local_reply(): DEBUG: local transaction completed

#------------------
# Flags
#------------------

debug=3
memdbg=5
mem_summary=5

#fork=no    # This option should not be present to enable forking but disable daemonize, also -D commandline parameter is needed
log_stderror=no
sip_warning=no

listen=172.28.4.128
port=6789
children=2
shm_mem_size=64

log_name="UACFailover"

check_via=no    # (cmd. line: -v)
dns=no          # (cmd. line: -r)
rev_dns=no      # (cmd. line: -R)
dns_use_search_list=no
use_dns_failover=yes
dns_srv_lb=yes
disable_tcp=yes

mpath="/usr/lib/x86_64-linux-gnu/kamailio/modules/"

loadmodule "pv.so"
loadmodule "tm.so"
loadmodule "tmx.so"
loadmodule "sl.so"
loadmodule "xlog.so"
loadmodule "rr.so"
loadmodule "uac.so"
loadmodule "rtimer.so"


# -----------------------------------------------------------------
# Module settings
# -----------------------------------------------------------------

modparam("pv", "varset", "server=s:LOGNAME")

modparam("tm", "auto_inv_100", 0)
# Time until provisional response (eg "100 Trying") is received
modparam("tm", "fr_timer", 2000)
# Time to await final response on INVITE per branch (eg per branch ring time)
modparam("tm", "fr_inv_timer", 10000)
# Time to await final response on INVITE (eg ring time)
modparam("tm", "max_inv_lifetime", 20000)
modparam("tm", "restart_fr_on_each_reply", 0)
modparam("tm", "failure_reply_mode", 3)

modparam("rtimer", "timer", "name=uac;interval=10;mode=1;")
modparam("rtimer", "exec", "timer=uac;route=TIMER")


route {
    xlog("L_NOTICE", "[$pr:$si:$sp] [$cs $rm] Request. (cid: $ci  <$fu> => <$ru>  len: $ml)");

    drop();
}


event_route[tm:local-request] {
    xlog("L_INFO", "  [$pr:$si:$sp] [$cs $rm] Request (cid: $ci  Branch: $T_branch_idx  ToTag: $tt  len:$ml) To <$ru> via <$du>");
}


onreply_route {
    xlog("L_INFO", "  [$pr:$si:$sp] [$cs $rm] Reply (cid: $ci  Branch: $T_branch_idx  Status: $rs $rr  ToTag: $tt  len:$ml)");
}


route[TIMER] {
    if not $var(done) == 1 {
        $var(done) = 1;
        $uac_req(method) = "OPTIONS";
        $uac_req(ruri) = "sip:failover.test.speakup.nl";
        $uac_req(furi) = "sip:from.example.com";
        $uac_req(turi) = "sip:to.example.com";
        xlog("L_INFO", "Sending $uac_req(method) request to $uac_req(ruri)");
        uac_req_send();
    }
}