Quick Demo Video Of Site Failover With KEMP Loadmaster Global Balancing


Here’s a quick video that demonstrates how you can achieve site failover with via the KEMP Loadmaster Global Balancing feature. As long as you know what this can do for you and realize that it about site failover and high availability and not continuous availability without a second of service interruption you can deliver nice results with this technology across city campuses or between cities.

In our scenario we normally connect to the primary data center (weighted round robin) and fail over to the DRC when the primary site fails for some reason.

It’s very busy at the moment but I hope to address this topic a bit more in detail in the future. All of this runs virtualized on Hyper-V and performs just fine.

Windows NLB On Windows Server 2012 R2 Hyper-V: A Personal Preferred Configuration Using IGMP With Multicast


To know and see the issues we are dealing with in this demo, you need to read this blog post first: Windows NLB Nodes “Misconfigured” after Simultaneous Live Migration on Windows Server 2012 (R2).

We were dealing with some issues on on several WNLB clusters running on a Windows Server 2012 R2 Hyper-V cluster after a migration from an older cluster. So go read that and come back Smile.

Are you back? Good.

Let’s look at the situation we’ll use to show case one possible solution to the issues. If you have  a 2 node Hyper-V cluster, are using NIC Teaming for the switch and depending on how teaming is set up you’ll might run into these issues. Here we’ll use a single switch to mimic a stacked one (the model available to me is non stackable and I have only one anyway).

  • Make sure you enable MAC Spoofing on the appropriate vNIC or vNICs in the advanced settings

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  • Note that there is no need to use a static MAC address or copy your VIP mac into the settings of your VM  with Windows Server 2012 (R2) Hyper-V
  • Set up WNLB with IGMP multicast as option. While chancing this there will be some advice warnings thrown at you Smile

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I’m not going in to the fact that since W2K8 the network default configurations are all about security. You might have to do some configuration work to get the network flow to do what it needs to do. Lots on this  weak host/strong host model behavior on the internet . Even wild messy ramblings by myself here.

On to the switch itself!

Why IGMP multicast? Unicast isn’t the best option and multicast might not cut it or be the best option for your environment and IGMP is less talked about yet it’s a nice solution with Windows NLB, bar replacing into with a hardware load balancer. For this demo I have a DELL PowerConnect 5424 at my disposal. Great little switch, many of them are still serving us well after 6 years on the job.

What MAC address do I feed my switch configurations?

Ah! You are a smart cookie, aren’t you. A mere ipconfig reveals only the unicast MAC address of the NIC. The GUI on WNLB shows you the MAC address of the VIP. Is that the correct one for my chosen option, unicast, multicast or IGMP multicast?  No worries, the GUI indeed shows the one you need based on the WNLB option you configure. Also, take a peak at nlb.exe /? and you’ll find a very useful option called ip2mac.

Let’s run that against our VIP:

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And compare it to what we see in the GUI, you’ll notice that show the MAC to use with IGMP multicast as well.

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You might want to get the MAC address before you configure WNLB from unicast to IGMP multicast. That’s where the ip2mac option comes in handy.

Configuring your switch(es)

We have a multicast IP address that we’ll convert into the one we need to use. Most switches like the PowerConnect 5424 in the example will do that for you by the way.

I’m not letting the joining of the members to the Bridge Multicast Group happen automatically so I need to configure this. I actually have to VLANs, each Hyper-V host has 2 LACP NIC team with Dynamic load balancing connected to an LACP LAGs on this switch (it’s a demo, yes, I know no switch redundancy).  I have tow as some WNLB nodes have multiple clusters and some of these are on another VLAN.

I create a Bridge Multicast Group. For this I need the VLAN, the IGMP multicast MAC address and cluster IP address

When I specify the IGMP multicast MAC I take care to format it correctly with “:” instead of “–“ or similar.

You can type in the VIP IP address or convert is per this KB yourself. If you don’t the switch will sort you out.

The address range of the multicast group that is used is 239.255.x.y, where x.y corresponds to the last two octets of the Network Load Balancing virtual IP address.

For us this means that our VIP of 172.31.3.232 becomes 239.255.3.232. The switch handles typing in either the VIP or the converted VIP equally well.

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This is what is looks like, here there are two WNLB clusters in ICMP multicast mode configured. There are more on the other VLAN.

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We leave Bridge Multicast Forwarding here for what it is, no need in this small setup. Same for IGMP Snooping. It’s enable globally and we’ve set the members statically.

We make unregistered multicast is set to forwarding (default).

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Basically, we’re good to go now. Looking at the counters of the interfaces & LAGs you should see that the multicast traffic is targeted at the members of the LAGs/LAGs and not all interfaces of the switch. The difference should be clear when you compare the counters adding up before and after you configured IGMP.

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The Results

No over the top switch flooding, I can simultaneously live migrate multiple WLNB nodes and have them land on the same switch without duplicate IP address warning. Will this work for you. I don’t know. There are some many permutations that I can’t tell you what you should do in your particular situation to make it work well. I’ll just quote myself from my previous blog post on this subject:

“"If you insist you want my support on this I’ll charge a least a thousand Euro per hour, effort based only. Really. And chances are I’ll spend 10 hours on it for you. Which means you could have bought 2 (redundancy) KEMP hardware NLB appliances and still have money left to fly business class to the USA and tour some national parks. Get the message?”

But you have seen some examples on how to address issues & get a decent configuration to keep WNLB humming along for a few more years. I really hope it helps out some of you struggling with it.

Wait, you forgot the duplicate IP Address Warning!

No, I didn’t. We’ll address that here. There are some causes for this:

  • There is a duplicate IP address. If so, you need to address this.
  • A duplicate IP address warning is to be expected when you switch between unicast and multicast NLB cluster modes (http://support.microsoft.com/kb/264645). Follow the advice in the KB article and clearing the ARP tables on the switches can help and you should get rid of it, it’s transient.
  • There are other cause that are described here Troubleshooting Network Load Balancing Clusters. All come down to the fact that somehow you’re getting multiple MAC address associated with the same IP address. One possible cause can be that you migrated form an old cluster to a new cluster, meaning that the pool of dynamic IP addresses is different and hence the generated VIP MAC … aha!
  • Another reason, and again associated multiple MAC address associated with the same IP address is that you have an old static ARP entry for that IP address somewhere on your switches. Do some house cleaning.
  • If all the above is perfectly fine and you’re certain this is due to some Hyper-V live migration, vSwitch, firmware, driver bug you can get rid of the warning by disabling ARP checks on the cluster members. Under HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters, create a DWORD value with as name “ArpRetryCount” and set the value to 0. Reboot the server for this to take effect. In general this is not a great idea to do. But if you manage your IP addresses well and are sure no static entries are set on the switch it can help avoid this issue. But please, don’t just disable “ArpRetryCount” and ignore the root causes.

Conclusion

You can still get WNLB to work for you properly, even today in 2014. But it’s time to start saying goodbye to Windows NLB. The way the advanced networking features are moving towards layer 3 means that “useful hacks” like MAC spoofing for Windows NLB are going no longer going to work.  But until you have implement hardware load balancing I hope this blog has given you some ideas & tips to keep Windows NLB running smoothly for now. I’ve done quite few and while it takes some detective work & testing, so far I have come out victorious. Eat that Windows NLB! I have always enjoyed making it work where people said it couldn’t be done. But with the growing important of network virtualization and layer 3 in our networks, this nice hack, has had it’s time.

For some reasons developers like Windows NLB as  “it’s easy and they are in control as it runs on their servers”. Well … as you have seen nothing comes free and perhaps our time is better spend in some advanced health checking and failover in hardware load balancing. DevOps anyone?

Windows NLB Nodes Misconfigured after Simultaneous Live Migration on Windows Server 2012 (R2)


Here’s the deal. While Windows NLB on Hyper-V guests might seem to work OK you can run into issues. Our biggest challenge was to keep the WNLB cluster functional when all or multiple node of the cluster are live migrated simultaneously. The live migration goes blazingly fast via SMB over RDMA nut afterwards we have a node or nodes in an problematic state and clients being send to them are having connectivity issues.

After live migrating multiple or all nodes of the Windows NLB cluster simultaneously the cluster ends up in this state:

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A misconfigured interface. If you click on the error for details you’ll see

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Not good, and no we did not add those IP addresses manually or so, we let the WNLB cluster handle that as it’s supposed to do. We saw this with both fixed MAC addresses (old school WNLB configuration of early Hyper-V deployments) and with dynamic MAC addresses. On all the nodes MAC spoofing is enabled on the appropriate vNICs.

The temporary fix is rather easy. However it’s a manual intervention and as such not a good solution. Open up the properties of the offending node or nodes (for every NLB cluster that running on that node, you might have multiple).

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Click “OK” to close it …

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… and you’re back in business.

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Scripting this out somehow with nlb.exe or PowerShell after a guest gets live migrated is not the way to go either.

But that’s not all. In some case you’ll get an extra error you can ignore if it’s not due to a real duplicate IP address on your network:

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We tried rebooting the guest, dumping and recreating the WNLB cluster configuration from scratch. Clearing the switches ARP tables. Nothing gave us a solid result.

No you might say, Who live migrates multiple WNLB nodes at the same time? Well any two node Hyper-V cluster that uses Cluster Aware Updating get’s into this situation and possibly bigger clusters as well when anti affinity is not configured or chose to keep guest on line over enforcing said anti affinity, during a drain for an intervention on a cluster perhaps etc. It happens. Now whether you’ll hit this issue depends on how you configure and use your switches and what configuration of LBFO you use for the vSwitches in Hyper-V.

How do we fix this?

First we need some back ground and there is way to much for one blog actually. So many permutations of vendors, switches, configurations, firmware & drivers …

Unicast

This is the default and Thomas Shinder has an aging but  great blog post on how it works and what the challenges are here. Read it. It you least good option and if you can you shouldn’t use it. With Hyper-V we and the inner workings and challenges of a vSwitch to the mix. Basically in virtualization Unicast is the least good option. Only use it if your network team won’t do it and you can’t get to the switch yourself. Or when the switch doesn’t support mapping a unicast IP to a multicast MAC address. Some tips if you want to use it:

  1. Don’t use NIC teaming for the virtual switch.
  2. If you do use NIC teaming for the virtual switch you should (must):
    • use switch independent teaming on two different switches.
    • If you have a stack or just one switch use multicast or even better IGMP with multicast to avoid issues.

I know, don’t shout at me, teaming on the same switch, but it does happen. At least it protects against NIC issues which are more common than switch or switch port failures.

Multicast

Again, read Thomas Shinder his great blog post on how it works and what the challenges are here.

It’s an OK option but I’ll only use it if I have a switch where I can’t do IGMP and even then I do hope I can do two things:

  1. Add a static entry for the cluster IP address  / MAC address on your switch if it doesn’t support IGMP multicast:
    • arp [ip] [cluster multicast mac*] ARPA  > arp 172.31.1.232  03bf.bc1f.0164 ARPA
  2. To prevent switch flooding occurs, as with the unicast configure your switch which ports to use for multicast traffic:
    • mac-address-table static [cluster multicast mac] [vlan id] [interface]  > mac-address-table static 03bf.bc1f.0164 vlan 10 interface Gi1/0/1

The big rotten thing here is that this is great when you’re dealing with physical servers. They don’t tend to jump form switch port to switch port and switch to switch on the fly like a virtual machine live migrating. You just can’t hardcode all the vSwitch ports into the physical switches, one they move and depending on the teaming choice there are multiple ports, switches etc …it’s not allowed and not possible. So when using multicast in a Hyper-V environment stick to 1). But here’s an interesting fact. Many switches that don’t support 1) do support 2). Fun fact is that most commodity switches do seems to support IGMP … and that’s your best choice anyway! Some high end switches don’t support WNLB well but in that category a hardware load balancer shouldn’t be an issue. But let’s move on to my preferred option.

  • IGMP With Multicast (see IGMP Support for Network Load Balancing)

    This is your best option and even on older, commodity switches like a DELL PowerConnect 5424 or 5448 you can configure this. It was introduced in Windows Server 2003 (did not exist in NT4.0 or W2K). It’s my favorite (well, I’d rather use hardware load balancing) in a virtual environment. It works well with live migration, prevents switch flooding and with some ingenuity and good management we can get rid of other quirks.

    So Didier, tell us, how to we get our cookie and eat it to?

    Well, I will share the IGMP with Multicast solution with you in a next blog. Do note that as stated above there are some many permutations of Windows, teaming, WNL, switches  & firmware/drivers out there I give no support and no guarantees. Also, I want to avoid writing a  100 white paper on this subject?. If you insist you want my support on this I’ll charge at least a thousand Euro per hour, effort based only. Really. And chances are I’ll spend 10 hours on it for you. Which means you could have bought 2 (redundancy) KEMP hardware NLB appliances and still have money left to fly business class to the USA and tour some national parks. Get the message?

    But don’t be sad. In the next blog we’ll discuss some NIC teaming for the vSwitch, NLB configuration with IGMP with Multicast and show you a simple DELL PowerConnect 5424 switch example that make WNLB work on a W2K12R2 Hyper-V cluster with NIC teaming for the vSwitch and avoids following issues:

    • Messed up WNLB configuration after the simultaneous live migration of all or multiple NLB Nodes.
    • You avoid “false” duplicate IP address goof ups (at the cost of  IP address hygiene management).
    • You prevent switch port flooding.

    I’d show you on redundant Force10 S4810 but for that I need someone to ship me some of those with SFP+ modules for the lab, free of cost for me to keep Winking smile

    Conclusion

    It’s time to start saying goodbye to Windows NLB. The way the advanced networking features are moving towards layer 3 means that “useful hacks” like MAC spoofing for Windows NLB are going no longer going to work.  But until you have implement hardware load balancing I hope this blog has given you some ideas & tips to keep Windows NLB running smoothly for now. I’ve done quite few and while it takes some detective work & testing, so far I have come out victorious. Eat that Windows NLB!

  • MVP Carsten Rachfahl Visits & Interviews Me On Networking & Storage in Windows Server 2012


    Last month Carsten (MVP – Virtual Machine) & Kerstin Rachfahl (MVP – Office 365) visited me in my home town. Apart from a short visit to the historic center & a sushi diner amongst friends we also did an interview where we discussed our ongoing Windows Server 2012 Hyper-V activities. We’re trying to leverage as much of the product we can to get the best TCO & ROI and as early adopters we’ve been reaping the benefits form the day the RTM bits were available to us. So far that has been delivering great results. Funny to hear me mention the Fast Track designs as a week later we saw version 3 of those at MMS2013. The most interesting to me about those was the fact that the small & medium sizes focus on Cluster in a Box and Storage Spaces!

    While we were having fun talking about the above we also enjoyed some of the most beautiful landmarks of the City of Ghent as a back drop for the interview. It was filmed in a meeting room at AGIV, to whom I provide Infrastructure services with a great team of colleagues. Just click the picture to view the video.

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    You can also enjoy the video on Carsten’s blog http://www.hyper-v-server.de/videos/interview-mit-didier-van-hoye-ber-seinen-storage-netwerk-und-mehr/ All I need to do now is to arrange for Carsten to physically touch the Compellent storage I think.

    Learning Resources for Windows 8 Clustering, WNLB & Hyper-V 3.0


    I know a lot of you are, just like me, actively investigating Windows 8 & Hyper-V. You’re downloading the Beta, reading blog post, discussing scenarios and use cases and that’s great. You’re investing in a bright future Smile

    Here are some blog post that contain gems of information and that I’d like to bring to your attention:

    Enjoy!

    Using Host Names in IIS in Combination with a KEMP LoadMaster


    At a client the change over of a web site from old servers to new ones lead to the investigation of an issue with the hardware load balancer. Since that web site is related to an existing surveyors solutions suite that already had a KEMP LoadMaster 2200 in use the figured we’d also use it for the web site and no longer use WNLB.

    Now the original web site had multiple DNS entries and host header names defined in IIS (see Configure a Host Header for a Web Site (IIS 7)) . Host header names in IIS allow you to host multiple web sites on an IIS server using the same IP address and port. A small added security benefit is that surfing on IP address fails which means we marginally disrupt some script kiddies & get an extra security checkbox marked during an audit Winking smile.

    In our example we needed:

    Note: The real names have been changed as well as the reasons why as this has some business & historical justifications that don’t matter here.

    ntrip.surveyor.lab needs to be handled by the load balanced web servers in the solution. The http://www.surveyor.lab needs to be redirected to another web server to keep the business happy. However for political reasons we have to keep the DNS record for http://www.surveyor.lab pointing to the load balanced servers, i.e. the load master VIP.

    Now without host names IIS al worked fine until we wanted to use HTTP redirect. As the web site is the same IP address for both names we either redirected them both or none. To fix this we needed two sites in IIS. The real one hosting ntrip.surveyor.lab and a “fake” one hosting the http://www.surveyor.lab that we want to redirect. Well as both are hosted on the same IP address and port on the IIS server we need to use host names. But then the sites became unavailable.

    When checking the LoadMaster configuration, the virtual service for the web servers seemed well.

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    Is this a limitation of hardware load balancing or this specific Loadmaster? Some searching on the internet made it look like I was about the only on on the planet dealing with this issue so no help there.

    Kemp Support Rocks

    I already knew this but this experience reaffirms it. KEMP Technologies really does care about their customers and are very fast & responsive. I threw a quick question on twitter to @KempTech on Twitter and they responded very fast with some pointers. After that I replied with some more details, they offered to take it on via other means as twitter has it limits. OK, no problems. The next morning I got an e-mail from one of their engineers (Ekkehard) with more information and a request for more input from our side. I quickly made a VISIO diagram of the current and the desired situation. Based on this he let me know this should work.

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    He asked for a copy of the configuration and already pointed to the solution:

    And what exactly happens – does the RS turn “red” in the “View/Modify Services” view? That might be caused by the health check settings…
    (Remember that a 302 is considered NOT ok, so you had to enter the proper check URL and or / HTTP1.1 hostname)

    But at that moment I did not realize this yet. I saw no error or the real server turning red indicating it was down. So we went through the configuration and decided to test without forcing layer 7 to see what happened. This didn’t make a difference and it wasn’t really a solution if it had as we needed layer 7 and layer 7 transparency.

    Ekkehard also noticed my firmware was getting rather old (don’t fix what isn’t broken Smile) and suggest an upgrade (5.1-24 to 5.1.-74). So I did, reboot and tested some more settings. To make sure I didn’t miss anything I threw a network sniffer (WireShark) against the issue. And guess what?  As soon as I added a host name to the IIS web site bindings I didn’t even get any request from my client on that server anymore. So it was definitely being stopped at the Loadmaster. Without it request from a client came through perfectly.  That was not IIS doing as with a host name nothing came into the server. So why would the LoadMaster stop traffic to a real server? Because it’s down, that’s why, just like Ekkehard has indicated in one of his mails but we didn’t see it then.

    Better check again and sure enough, the health service told me the real servers are down. Hey … that’s new. Did the previous firmware not show this, or just slower? I can’t say for sure. It’s either me being to impatient, a hiccup, the firmware or premature dementia Confused smile

    Root Cause

    So what happens? The default health check uses HTTP 1.0. You can customize it with a path like  /owa or such but in essence it uses the IP address of the real server and guess what. With a Host header name in IIS that isn’t allowed other wise it can’t figure out what website you want to go to if you’re using this feature to run multiple sites on the same IP address and port. So we need to check the health based on host name. Can the LoadMaster do that for us? Yes it can!

    The fix

    You need to enable HTTP 1.1 and fill out the host name you want to use for health checking.  In our case that’s ntrip.surveyor.lab. That’s all there’s to it. Easy as can be if you know. And Ekkehard knew he indicated to this in his quoted mail above.

    HTTP1 1host

     

    Lessons Learned

    So how did I not know this? Isn’t this documented? Sure enough on page  56 of the LoadMaster manual it says the following:

    7  HTTP  The LoadMaster opens a TCP connection to the Real Server on the Service port (port80). The LoadMaster sends a HTTP/1.0 HEAD request the server, requesting the page ―/‖.  If the server sends a HTTP response with a status code of 2 (200-299, 301, 302, 401) the LoadMaster closes the connection and marks the server as active.  If the server fails to respond within the configured response time for the configured number of times or if it responds with a different status code, it is assumed dead.  HTTP 1.0 and 1.1 support available, using HTTP 1.1 allows you to check host header enabled web servers.

    Typical, you read the exact line of information you need AND understand it after having figured it out. Now linking that information (yes we always read all manuals completely Embarrassed smile) to the situation at hand isn’t always that fast a process but I got there in the end with some help from KEMP Technologies.

    One hint is perhaps to mention this is in the handy tips that pop up when you hover over a setting in the LoadMaster console. I rely on this a lot and a mention of “HTTP 1.1 allows you to check host header enabled web servers” might have helped me out. But it’s not there. A very poor excuse I know … Embarrassed smile

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    Host Header Names & HTTP redirection

    After having fix this issue I proceeded to configure HTTP redirect in IIS 7.5. For this is used two sites. One was just a fake site tied to the www.surveyors.lab hostname in IIS on port 80.

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    For this site I created a HTTP redirect to www.bussines.lab/surveyors/services. This works just fine as long as you don’t forget the http:// in the redirect URL.

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    So it has to be http://www.bussines.lab/surveyors/services or you’ll get a funky loop effect looking like this:

    http://www.surveyors.lab/www.bussines.lab/surveyors/services/www.bussines.lab/surveyors/services/www.bussines.lab/surveyors/services

    Firefox will tell you you have a loop that will never end but Internet Explorer doesn’t, it just fails. You do get that URL as a pointer to the cause of the issue. That is if you can relate it to that.

    The other was the real site  and was configured with following bindings and without redirection.

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    Don’t forget to do this on all real servers in the farm! The next thing I need to find out is how to health check two host names in the LoadMaster as I have two websites with the same IP address, port but different host names.

    Hyper-V, KEMP LoadMaster & DFS Replication Provide FTP Solutions For Surveyors Network


    Remember the blog entry about A Hardware Load Balancing Exercise With A Kemp Loadmaster 2200 KEMP Loadmaster to provide redundancy for a surveyors GPS network? Well, we got commissioned to come up with a redundant FTP solution for their needs last month and this blog is about what we came up with. The aim was to make due with what is already available.

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    FTP 7.5 in Windows 2008 R2

    We use the FTP Server available in Windows 2008 R2 which provides us with all functionality we need: User Isolation and FTP over SSL.

    The data from all the GPS stations is sent to the FTP server for safe keeping and is to be used to overcome certain issues customers might have with missing data from surveying solution. This data is not being made available to customers by default, it’s only for special cases & purposes. So we need to collect the data in its own folder named after its account so we can configure user isolation. This also prevents the GPS Stations from writing in locations where it shouldn’t.

    As every GPS Station slogs in with the “Station” account it ends up in the “Station” folder as root FTP folder and can’t read or write out of that folder. The survey solution service desk can FTP into that folder and access any data they want.

    The data that’s being provided by the software solution (LanSurvey01 and lanSurvey02) is to be sent to its own folder “Data” that is also set up with user Isolation to prevent the application from reading or writing anywhere else on the file system.

    The data from should be publicly available to the customers and for this we created a separate FTP site called “Public” that is configured for anonymous access to the same Data folder but with read permissions only. This way the customers can get all the data they need but only have read access to the required data and nothing more.

    For more information on setting up FTP 7.5 and using FTP over SSL you might take a look here http://learn.iis.net/page.aspx/304/using-ftp-over-ssl/ and read my blog on FTP over SSL Pollution of the Gene Pool a Real Life “FTP over SSL” Story

    High Availability

    In the section above we’ve taken care of the FTP needs. Now we still need redundancy. We could use Windows NLB but since this network already uses a KEMP Loadmaster due to the fact that the surveyor’s software has some limitations in its configuration capabilities that doesn’t allow Windows Network Load Balancing being used.

    We want both the GPS stations and the surveyor’s application servers to be able to send FTP data when one of the receiving FTF servers is down for some reason (updates, upgrades, maintenance or failure). What we did is set up a VIP for use with FTP on the Kemp Loadmaster. This VIP is what is used by the GPS Stations and the application to write and by the customers to read the FTP data.

    DFS-R to complete the solution

    But up until now we’ve been ignoring an issue. When using NLB to push data to hosts we need to ensure that all the data will be available on all the nodes all of the time. You could opt to only have the users access the FTP service via a NLB VIP address and push the data to both nodes without using NLB. The latter might be done at the source but then you have twice the amount of data to push out. It also means extra work to configure and maintain the solution. We could copy the data to one FTP node and copy it from there. That works but leaves you very vulnerable to a service outage when the node that gets the original copy is down. No new data will be available. Another issue is the fact that you need a rock solid way to copy the data and have it done it a timely manner, even after down time of one or more of the nodes.

    As you read above we provide a NLB VIP as a target for the surveyor’s application and the GPS Stations to send their data to. This means the data will be sent to the FTP NLB array even if one of the nodes is down for some reason. To get the data that arrives from 2 application servers and from 40 GPS Stations synchronized and up to date on both the NLB nodes we use the Data File System – Replication (DFS-R) built into Windows 2008 R2. We have no need for a DFS-Namespace here, so we only use the replication feature. This is easy and fast to set up (add the DFS service from the File Server Role) and it doesn’t require any service down time (no reboot required). The fact that both the FTP nodes are member of a Windows 2008 R2 domain does help with making this easy. To make sure we have replication in all direction we opt to set it up as a full and the replication schedule is 24/7, no days off J Since we chose to replicate the FTP root folder we have both the Data and the Stations folders covered as well as the folder structure needed to have FTP user Isolation function.

    This solution was built fast and easily using Windows 2008 R2 out of the box functionality: FTP(S) with User Isolation and DFS-R. The servers are running as hyper-V guests in a Hyper-V cluster providing high availability through Live Migration.