Big-IP and ADFS Part 5 – “Working with ADFS 3.0 and SNI”
Can you believe it? It’s true, it’s true! There’s a part 5. What can I say? Times change; people change; software changes. Active Directory Federation Services, (ADFS) is no exception. While the BIG-IP with SAML 2.0 can alleviate the need for and ADFS infrastructure in many use cases, there are still organizations that need/want to continue utilizing ADFS. Fortunately, regardless of which way you go, F5 can help. So, in the spirit of free will, collaboration, and serving the greater good, (too much?), let’s talk about load balancing ADFS 3.0 with the BIG-IP.
As you may, or may not, recall the previous posts around BIG-IP and ADFS revolved around load balancing ADFS 2.0 and ADFS Proxy, replacing the ADFS Proxy with Access Policy Manager, and replacing the entire ADFS infrastructure with APM and SAML. The good news is that these posts are still relevant with regards to ADFS 3.0 and the ADFS proxy replacement, (WAP); well for the most part anyway.
ADFS and SNI
While there are numerous differences between ADFS 3.0 and previous versions, the most significant change with respect to providing HA and scalability for the ADFS 3.0 infrastructure is its use of Server Name Indication, (SNI). To Successfully integrate a load balancing solution, ( including full reverse proxy), into the ADFS environment the device must support SNI. The load balancing device must be able to present the server name to the backend host as part of the initial Client Hello. Fortunately, the BIG-IP, (ver. 11.1.0 and later) supports this TLS protocol extension.
The rest of this post will provide guidance on enabling SNI support for ADFS 3.0 integration. For overall guidance refer to parts one thru three of this series as well as the recently published ADFS 2.0 Deployment Guide.
SNI and the Server Profile
The BIG-IP provides a virtual server, (listener), that receives client SSL connections and subsequently intelligently passes traffic into a pool of ADFS/WAP servers. Depending upon the organization’s infrastructure and security requirements, the BIG-IP can simply receive encrypted client connections and pass them through to the backend ADFS farm, (aka SSL tunneling). However, the preferred method, (SSL bridging), receives encrypted clients connections; terminates and decrypts the traffic. The traffic is then re-encrypted and sent to the backend application servers. This method adds an additional layer of security since external traffic never directly connects to the internal domain-joined machines as well affording the ability to perform additional deep packet inspection.
SSL bridging back to the ADFS farm requires associating a server SSL profile to the virtual server. Enabling SNI is simply a matter of specifying the server name on the associated server SSL profile, (see below).
1. Navigate to the appropriate profile;
2. Select ‘Advanced’ configuration and enter the FQDN of the backend ADFS service hostname. The hostname will now be provided during the TLS negotiation. In the example below, the server name is ‘fs.f5demo.net’, (refer to the highlighted field). Like I said, simple!
Health Monitoring and SNI
Effectively monitoring the backend ADFS/WAP farm members is a little trickier but very doable. Since the built-in HTTP monitors do not provide the server name as part of the TLS negotiation, using them will result in the being backend servers being incorrectly marked as down, (not good).
You could simply use a non-HTTP monitor, (ICMP being the most common), but that doesn’t provide a reasonable guarantee that the actual ADFS service is functioning. Better than that, what we can do is create an external custom SNI enabled monitor that validates the service metadata and associate it to the pool. It’s as easy as 1,2,3,…..um.. 4,5,6.
1. Download the script: http://www.f5.com/pdf/deployment-guides/sni-eav.zip
2. Upload the previously downloaded file into the BIG-IP via the web interface. Navigate to ‘System’ –> ‘External Monitor Program List’ –> ‘Import’;
IMPORTANT!!!
If ADFS proxy server is configured to accept SSL/TLS connections only using TLSv1.1 or better , the monitor will not work.
If have come up with this one-liner to replace the “curl” based command in the script. Thanks to Jerry Tower for helping fix the actual HTTP request as well as testing the script.
(echo -e "GET $URI HTTP/1.1\r\nHost: $HOST\r\nConnection: Close\r\n\r\n"; sleep 2) | openssl s_client –quiet –servername $HOST -connect $NODE:$PORT 2> /dev/null| grep -i "$RECV" 2>&1> /dev/null
The script line that this one-liner should replace is the following:
curl-apd -k -v -i --resolve $HOST:$PORT:$NODE https://$HOST$URI | grep -i "${RECV}" 2>&1 > /dev/null
3. Browse to and select the file. Provide a name for the file and select ‘Import’;
4. Create a new external monitor utilizing the associate external file. Navigate to ‘Local Traffic’ –> ‘+’ sign;
5. Provide a name and select ‘External’ for the type. Select the previously created external program. The script provided requires three, (3) variables entered as name/value pairs. The variables are listed below. Select ‘Finished’;
|
Name | Value |
| RECV | HTTP/1.1 200 |
| URI | /FederationMetadata/2007-06/FederationMetadata.xml |
| HOST |
6. Associate the newly created monitor to the ADFS pool and/or the WAP pool. Select ‘Local Traffic’ –> ‘Pools’ –> ‘Pool List’. Move the monitor into the active pane and select ‘Update’.
Additional Links:
Big-IP and ADFS Part 1 – “Load balancing the ADFS Farm”
Big-IP and ADFS Part 2 – “APM–An Alternative to the ADFS Proxy”
Big-IP and ADFS Part 3 – “ADFS, APM, and the Office 365 Thick Clients”
Big-IP and ADFS Part 4 – “What about Single Sign-Out?”
BIG-IP Access Policy Manager (APM) Wiki Home - DevCentral Wiki
Published May 30, 2014
Version 1.0
Greg_Coward
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rmd1023Nimbostratus
I ended up making things work with a slight variant of a script linked from this article - for some reason the HOST, RECV, and URI variable definitions early in the script weren't working, which made everything go pear-shaped, so I hardcoded them in. This means I'll have to write a separate script for each different federated server I set up since the hostname (here, "fedserver.example.com") will be different for each external script. The node and port are correctly passed to the script by the monitor itself, so we don't have to write a separate script for each node or anything wacky like that. Uploaded the script through "System->File Management->External Monitor Program File List" and was able to use it in a new external monitor.
Here's my edited script:
!/bin/sh These arguments supplied automatically for all external monitors: $1 = IP (nnn.nnn.nnn.nnn notation) $2 = port (decimal, host byte order) This script expects the following Name/Value pairs: HOST = fedserver.example.com. URI = /FederationMetadata/2007-06/FederationMetadata.xml RECV = HTTP/1.1 200 Remove IPv6/IPv4 compatibility prefix (LTM passes addresses in IPv6 format) NODE=`echo ${1} | sed 's/::ffff://'` if [[ $NODE =~ ^[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}$ ]]; then NODE=${NODE} else NODE=[${NODE}] fi PORT=${2} PIDFILE="/var/run/`basename ${0}`.sni_monitor_fedserver.example.com_${PORT}_${NODE}.pid" if [ -f $PIDFILE ] then echo "EAV exceeded runtime needed to kill fedserver.example.com:${PORT}:${NODE}" | logger -p local0.error kill -9 `cat $PIDFILE` > /dev/null 2>&1 fi echo "$$" > $PIDFILE curl-apd -k -v -i --resolve fedserver.example.com:$PORT:$NODE https://fedserver.example.com/FederationMetadata/2007-06/FederationMetadata.xml| grep -i "HTTP/1.1 200" 2>&1 > /dev/null STATUS=$? rm -f $PIDFILE if [ $STATUS -eq 0 ] then echo "UP" fi exit
dav_103788I could make it work on BIG-IP 11.5.3 Build 2.0.196 Hotfix HF2. Don't know why but, as soon as the script is updated through the GUI ( with or without modification ), the script appears in the directory /tmp and the check is OK, before ( just after uploading the script and creating the monitor ) I could not find it on the disk and the check was KO.
I have also tested with or without the "()", it works in both cases.
MS_273769I removed the () before the echo and it worked for me.
echo -e "GET $URI HTTP/1.1\r\nHost: $HOST\r\nConnection: Close\r\n\r\n"; sleep 2 | openssl s_client –quiet –servername $HOST -connect $NODE:$PORT 2> /dev/null| grep -i "$RECV" 2>&1> /dev/null- ReneeIs there a reason to use /FederationMetadata/2007-06/FederationMetadata.xml as the URI value vs /adfs/fs/federationserverservice.asmx which is what is in the deployment guide? Both seem to work fine. Thanks
JohnNordien_178Hello, Thank you for writing this servies of articles! I have some questions regarding this article, and the series in general. 1. Under Step 2 of section "SNI and the Server Profile" is the picture of SCVMM really the correct picture? 2. I am still confused about the Health Monitoring script. Is the command on line 31 "curl-apd -k -v ..." or is it "curl -apd -k -v ..."? 3. A colleague of mine has recently returned from a Microsoft Technical course on ADFS 3 on Server 2012 R2 and he now wants to deploy 2 Microsoft WAP serversin our DMZ and relegate our DMZ F5 HA pair to a simple load balancing function. I am having a hard time trying to rationalize how MS WAP has capabilities that F5 cannot handle. Is there any valid reason that this must be deployed this way?- Jason_AdamsWithout running curl with the "-q" option, the STATUS section is moot. Change: curl-apd -k -v --resolve $SNI:$PORT:$NODE https://$SNI$URI 2>&1 > /dev/null | grep -i "${RECV}" TO: curl-apd -k -v --resolve $SNI:$PORT:$NODE https://$SNI$URI 2>&1 > /dev/null | grep -i -q "${RECV}"
- ustoun_185737btw, it looks like it should NOT be a 'space' in command 'curl -apd as stated by 'Dragan' it's 'curl-apd' as the command and and 'curl -apd' as the parameters to 'curl' command
- Chainsaw_9167Another possibility perhaps. Do you really need an external monitor? Never use an external monitor when a built-in one will work as well. Forking a shell and running even the simplest shell script takes a significant amount of system resources, so external monitors should be avoided whenever possible. If possible, have the server administrator script execution of the required transaction on the server itself (or locate/author an alternative script on the server) that reliably reflects its availability. Then, instead of an external monitor, you can define a built-in monitor that requests that dynamic script from the server, and let the server run the script locally and report results. For example, the simple request/response HTTP transaction in the sample script below would be much better implemented using the built in basic HTTP monitor. We can use the built in monitors until F5 add SNI capability without the performance hit. see links below There is another alternative. http://blogs.technet.com/b/applicationproxyblog/archive/2014/06/19/how-to-support-non-sni-capable-clients-with-web-application-proxy-and-ad-fs-2012-r2.aspx A very useful tool for manipulating http.sys http://www.codeproject.com/Articles/437733/Demystify-http-sys-with-HttpSysManager Hope this provides another perspective.
Victor_12567where are the instructions for OS version 10.2.4?- the --resolve option in the script is only available in curl starting version 7.21.3. TMOS 11.5.1 hf4 is using 7.19.7 and does not have this option..... On what version of TMOS has this been tested???
