external monitor GTM
We are using an external monitor on our F5 GTM (version 12.1.2) for sending curl statements to an openshift platform (https call constructed with DNS name & uri). Up till now this seemed to be working. But now for some applications hosted on this openshift platform , we are seeing strange behavior , when testing in CLI with curl statement like "curl -skv https://<application-name>/probe/liveness" --> 2 out of 3 requests are coming back with "HTTP /1.1 200 ok" which is the expected answer --> 1 out of 3 requests is coming back with 'HTTP /1.0 503 " We also have some LTM units in same network & when doing the same request from LTM , we always get the "HTTP /1.1 200 ok" . So the behavior seems only to be present on GTM , not LTM units. When diving into SSL answers which are failing we mainly notice : * server is presenting different certificates (failing call is using different certificate than the ones that are working) * failing calls we see answer coming back in http /1.0 and giving a 503 response (rather than answering in 1.1 My main problem is that we are only seeing this kind of behavior on GTM . We never have this behavior on LTM units & even tested from other stations .bit here we are always getting the correct answer .F5 DNS/GTM External Monitor(EAV) with SNI support and response code check
I have used this monitor for XC Distributed Cloud as the HTTP LB share by default the same tenant IP address and SNI support is needed. You can order dedicated public IP addresses for each HTTP LB and enable "Default Load Balancer" ( https://my.f5.com/manage/s/article/K000152902 ) option but it will cost you extra 😉 The script is a modified version of External https health monitor for SNI-enabled pool as to handle response codes and to set the SNI globally for the entire pool and it's members. If you are uploading from Windows machine see External monitor fails to run as you could hit the bug. This could be needed for F5 DNS/GTM below 16.1 that do not support SNI in HTTPS monitors. The only mandatory variable is "SNI" that should be set in the external monitor config that references this uploaded bash script. The "URI" variable by default is set to "/" and "$2" variable by default is empty or 443, the default expected response code 200. #!/bin/sh # External monitoring script for checking HTTP status code # $1 = IP (::ffff:nnn.nnn.nnn.nnn notation or hostname) # $2 = port (optional; defaults to 443 if not provided) # Default SNI to IP if not explicitly provided node_ip=$(echo "$1" | sed 's/::ffff://') # Remove IPv6 compatibility prefix SNI=${SNI:-"$node_ip"} # Assign sanitized IP to SNI # Default variables MON_NAME=${MON_NAME:-"MyExtMon$$"} pidfile="/var/run/$MON_NAME.$1..$2.pid" # PID file path DEBUG=${DEBUG:-0} # Enable debugging if set to 1 EXPECTED_STATUS=${EXPECTED_STATUS:-200} # Default HTTP status code to 200 URI=${URI:-"/"} # Default URI DEFAULT_PORT=443 # Default port (used if $2 is unset) # Set port to default if $2 is not provided if [ -z "${2}" ]; then PORT=${DEFAULT_PORT} else PORT=${2} fi # Kill old process if pidfile exists if [ -f "$pidfile" ]; then kill -9 -$(cat "$pidfile") > /dev/null 2>&1 fi echo "$$" > "$pidfile" # Perform the HTTP(S) request via single curl (fetch status code only) status_code=$(curl -s -o /dev/null -w '%{http_code}' --connect-timeout 5 --resolve "${SNI}:${PORT}:${node_ip}" "https://${SNI}:${PORT}${URI}") # Cleanup rm -f "$pidfile" > /dev/null 2>&1 # Output server status based on HTTP status code match if [ "$status_code" -eq "$EXPECTED_STATUS" ]; then echo "up" else echo "down" fi # Debugging if [ "$DEBUG" -eq 1 ]; then echo "Debugging on..." echo "SNI=${SNI}" echo "URI=${URI}" echo "IP=${node_ip}" echo "PORT=${PORT}" echo "MON_NAME=${MON_NAME}" echo "STATUS_CODE=${status_code}" echo "EXPECTED_STATUS=${EXPECTED_STATUS}" echo "curl -s -o /dev/null -w '%{http_code}' --connect-timeout 5 --resolve ${SNI}:${PORT}:${node_ip} https://${SNI}:${PORT}${URI}" fi
