haproxy[4014]: backend activation-backend has no server available!

[kcr]

Hi Team
we need your help to resolve the issue, we are getting 503 error intermittently for our servers.

haproxy configuration:
#log 127.0.0.1 local2 debug
log 127.0.0.1:514 local0 debug
chroot /var/lib/haproxy
pidfile /var/run/haproxy.pid
maxconn 10000
user haproxy
group haproxy
daemon
debug
tune.ssl.default-dh-param 2048

turn on stats unix socket

stats socket /var/lib/haproxy/stats
default

mode http
log global
option httplog
option dontlognull
option http-server-close
option forwardfor except 127.0.0.0/8
option redispatch
retries 3
timeout http-request 30s
timeout queue 1m
timeout connect 30s
timeout client 1m
timeout server 1m
timeout http-keep-alive 30s
timeout check 30s
maxconn 10000
backend activation-backend
balance roundrobin
http-send-name-header Host
http-response add-header XX-powered-by “West-1”
server XXXXXXX.com:443 XXXXXXX.com:443 check ssl verify none

output : for haproxy -vv
HA-Proxy version 1.8.27-493ce0b 2020/11/06
Copyright 2000-2020 Willy Tarreau willy@haproxy.org

Build options :
TARGET = linux2628
CPU = generic
CC = gcc
CFLAGS = -O2 -g -fno-strict-aliasing -Wdeclaration-after-statement -fwrapv -W no-null-dereference -Wno-unused-label -Wno-stringop-overflow
OPTIONS = USE_LINUX_TPROXY=1 USE_CRYPT_H=1 USE_GETADDRINFO=1 USE_ZLIB=1 USE_RE GPARM=1 USE_OPENSSL=1 USE_LUA=1 USE_SYSTEMD=1 USE_PCRE=1

Default settings :
maxconn = 2000, bufsize = 16384, maxrewrite = 1024, maxpollevents = 200

Built with OpenSSL version : OpenSSL 1.1.1g FIPS 21 Apr 2020
Running on OpenSSL version : OpenSSL 1.1.1k FIPS 25 Mar 2021
OpenSSL library supports TLS extensions : yes
OpenSSL library supports SNI : yes
OpenSSL library supports : TLSv1.0 TLSv1.1 TLSv1.2 TLSv1.3
Built with Lua version : Lua 5.3.4
Built with transparent proxy support using: IP_TRANSPARENT IPV6_TRANSPARENT IP_F REEBIND
Encrypted password support via crypt(3): yes
Built with multi-threading support.
Built with PCRE version : 8.42 2018-03-20
Running on PCRE version : 8.42 2018-03-20
PCRE library supports JIT : no (USE_PCRE_JIT not set)
Built with zlib version : 1.2.11
Running on zlib version : 1.2.11
Compression algorithms supported : identity(“identity”), deflate(“deflate”), raw -deflate(“deflate”), gzip(“gzip”)
Built with network namespace support.

Available polling systems :
epoll : pref=300, test result OK
poll : pref=200, test result OK
select : pref=150, test result OK
Total: 3 (3 usable), will use epoll.

Available filters :
[SPOE] spoe
[COMP] compression
[TRACE] trace

errors: May 26 10:16:31 localhost haproxy[4083320]: Server xxxxx-backend/XXXXX.com:443 is DOWN, reason: Layer6 timeout, check duration: 2002ms. 0 active and 0 backup servers left. 0 sessions active, 0 requeued, 0 remaining in queue
Message from syslogd@localhost at May 30 02:32:33 …
haproxy[104161]: backend activation-backend has no server available!

any possible solutions to resolve the issue.