Using a BIG-IP EAV external monitor to monitor HTTP/2 h2c servers

Problem this snippet solves:


Beginning in BIG-IP 14.1.0, F5 provides full proxy (client and server side) support for the HTTP/2 protocol. HTTP/2 connections can run over HTTP without TLS in plaintext or HTTPS with TLS encryption. h2 is the protocol identifier for HTTP/2 with TLS and h2c identifies HTTP/2 without TLS.

Note: Modern browsers today do not support HTTP/2 unencrypted.

Beginning in BIG-IP 15.1.0, F5 introduces 2 new HTTP/2 monitors, http2 and http2_head_f5. They monitor HTTP/2 over TLS but do not monitor h2c. This article describes how you can use Extended Application Verification, EAV or extended monitors to monitor the h2c health of your pool members and nodes.

BIG-IP Extended monitors

The built-in BIG-IP http2 and http2_head_f5 monitors perform monitoring using HTTP/2 over TLS, while your h2c pool members, which serve content using HTTP/2 on TCP will fail both monitor health checks. Instead, you can configure external monitors to do this. External monitors let you create custom scripts that contain specific logic that is not available in built-in BIG-IP monitors to monitor the health of pool members and nodes. For a complete overview of EAV external monitors and the procedure to implement one, refer to K71282813: Overview of BIG-IP EAV external monitors.

An important component of an external monitor is the script which runs a command such as curl or netcat that interacts with the pool member. To monitor h2c service, beginning in BIG-IP 14.1.0, you can use the nghttp command. nghttp differs from curl in how it negotiates and establishes HTTP/2 in the following way:

  • Upgrade header: curl negotiates HTTP/2 by sending an Upgrade header within an HTTP/1.1 connection and switching protocols to HTTP/2. The following is an example:
# curl --http2 -Ik
HTTP/1.1 101 Switching Protocols
Upgrade: h2c
Connection: Upgrade
HTTP/2.0 200
  • Direct: nghttp negotiates HTTP/2 by sending HTTP/2 frames directly to the pool member. The following example shows nghttp sending the initial HTTP/2 SETTINGS frame right after TCP is established.
# nghttp -nv
[ 0.000] Connected
[ 0.001] send SETTINGS frame <length=12, flags=0x00, stream_id=0>

How to use this snippet:

The external monitor script

The external monitoring script in this article uses the nghttp command as follows:

nghttp -v http://${node_ip}:${2}${URI} 2> /dev/null | grep -E -i "${RECV}" > /dev/null

The server response is piped to grep the ${RECV} variable. When grep is successful, it returns exit status code 0 and the h2c service of the server is marked up.

Note: When a command in the script sends any data or output to stdout, the script exits and the external monitor marks the pool member up. For example, if you include an echo up command at the top of your script, the external monitor marks the pool member up and the rest of the code below the command does not run.

External script implementation

To implement an h2c external monitor, copy and paste the following code and follow the procedure in K71282813: Overview of BIG-IP EAV external monitors.

  • You must define the RECV string in the Variables parameter of your BIG-IP external monitor on the Configuration utility. This is because referring to the nghttp command described above in the script, when RECV is undefined, the grep command will always return status code 0, thereby erroneously marking the pool member up.
  • Optionally define the URI parameter as appropriate in your environment. For example, you can define URI as /index.html.

Code :


# (c) Copyright 1996-2006, 2010-2013 F5 Networks, Inc.
# This software is confidential and may contain trade secrets that are the
# property of F5 Networks, Inc.  No part of the software may be disclosed
# to other parties without the express written consent of F5 Networks, Inc.
# It is against the law to copy the software.  No part of the software may
# be reproduced, transmitted, or distributed in any form or by any means,
# electronic or mechanical, including photocopying, recording, or information
# storage and retrieval systems, for any purpose without the express written
# permission of F5 Networks, Inc.  Our services are only available for legal
# users of the program, for instance in the event that we extend our services
# by offering the updating of files via the Internet.
# @(#) $Id: //depot/maint/bigip16.0.0/tm_daemon/monitors/sample_monitor#1 $
# these arguments supplied automatically for all external pingers:
# $1 = IP (::ffff:nnn.nnn.nnn.nnn notation or hostname)
# $2 = port (decimal, host byte order)
# $3 and higher = additional arguments
# $MONITOR_NAME = name of the monitor
# In this sample script, $3 is the regular expression

# Name of the pidfile

# Send signal to the process group to kill our former self and any children 
# as external monitors are run with SIGHUP blocked
if [ -f $pidfile ]
   kill -9 -`cat $pidfile` > /dev/null 2>&1

echo "$$" > $pidfile

# Remove the IPv6/IPv4 compatibility prefix 
node_ip=`echo $1 | sed 's/::ffff://'`

# Using the nghttp utility to get data from the server. 
# Search the data received for the expected expression.
nghttp -v http://${node_ip}:${2}${URI} 2> /dev/null | grep -E -i "${RECV}" > /dev/null


if [ $status -eq 0 ]
# Remove the pidfile before the script echoes anything to stdout and is killed by bigd      
    rm -f $pidfile
    echo "up"

# Remove the pidfile before the script ends
rm -f $pidfile

Tested this on version:

No Version Found
Published Oct 29, 2020
Version 1.0

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