Click here to close now.

Welcome!

AJAX & REA Authors: XebiaLabs Blog, Carmen Gonzalez, Jackie Kahle, Elizabeth White, Cloud Best Practices Network

Blog Feed Post

Lync 2013 High Availability deep dive: Architecture

With the release of Lync 2013 the story of high availability has changed significantly. Since these changes contain some new technologies I think it would be best to break this article out into multiple parts. For this first part, we will discuss the Architecture and that will be followed by the end user experience. There is a lot to discuss so let's get started.

Windows Fabric

One of the major changes is how Lync provides highly available services with a pool. In Lync 2010 this responsibility was handled by Cluster Manager. With Lync 2013 we now leverage the Windows Fabric to provide high availability to these services. The Windows Fabric services allows Lync to increase our scale for both On-Premise and Online deployments. Windows Fabric will handle the following:

  • Election of Primary, Secondary, and Backup Secondary replica
  • Failover Management including Fast Failover with full service
  • Replication between primary and secondary replicas
  • Manages and Monitors which servers are functional and participating in pool operations
  • Services for MCU Factory, Conference Directory, Routing Group, LYSS
  • Load Balancing within a pool

Data Replication within the Pool

  1. Persistent User Data – synchronous replication to all replicas
    1. Presence, Contacts and Groups, and User Voice settings
    2. Minimal Conference data including the Active Conference Roster and MCUs
    3. Transient User Data – not replicated across all replicas
      1. Presence changes due to user activity including Calendar, Inactivity, and Phone Calls.

The fabric will also lazily write this data to the backend end databases. Doing this lazily means when there are free cycles we will use them to replicate this data instead of impacting the server when its busy doing other replication to front ends. The backend data can be used for both rehydration of front end servers (restarts) and disaster recovery (pool failovers and failbacks).

The following ports must be opened between the Lync front end servers within a pool for the fabric replication process to be successful.

  • Federation (TCP/5090) - Windows Fabric ring communication.
  • Lease Agent (TCP/5091)
  • Client Connection (TCP/5092) - These are not user clients but Lync Services that register to Windows Fabric.
  • Runtime Service (TCP/5093)
  • Replication (TCP/5094)

 

Quorum

In order to function the Windows Fabric needs to achieve a status of Quorum. This means a certain number of servers (Voters) must be able to communicate with each other to ensure that the pool is capable of maintaining consistency (Quorum). There are 2 different pool states in which we must maintain\achieve quorum which differ in how many voters must be available.

  1. Cold Pool Startup\Quorum Lost – when a pool is first starting or after quorum has been lost, that pool must have roughly 85% of its servers available to achieve quorum1.
  2. Operating Pool – after a pool has been started we need at least 50% of the servers available to maintain quorum2.

1 This means that when defining a pool within topology builder only add the servers that will be deployed at that time, not in the future. If you put 6 servers in a pool within topology builder and only deploy 3, we will never achieve quorum because we don’t have approximitley 85% of the servers operational. Thus, the front end services will never start.

2 If quorum is lost then all Front End services will be shutdown to protect the cluster from data loss.

To identify the Quorum voters a given servers Windows Fabric identifies check C:\ProgramData\Windows Fabric\Settings.xml. This file is updated when the Windows Fabric Host service starts up, thus any changes to pool members requires a service restart on all Front Ends in the pool, one at a time. The To-Do list in topology builder lets you know that after publishing the topology. If this isn't completed your servers will have a skewed view of the topology which could cause issues.  Depending on the number of servers within the pool, this will dictate which voters are required.

  1. Even # Server Pool (Figure 1) – each server will have 1 vote and the SQL instance will have 1 vote. The SQL server will act as a tiebreaker.
  2. Odd #Server Pool (Figure 2) – each server will have 1 vote.

Figure 1: Even number of servers in Front End Pool

Figure 2: Odd number of servers in Front End pool

 

Routing Groups

When users are provisioned for Lync they are assigned to Routing groups. Each routing group will contain 3 replicas: primary, secondary, and backup secondary which together are called a replica set. User services for all users will be handled by their primary replica. All users in the same routing group will be homed on the primary replica. If the primary replica fails, all users in that Routing Group will failover to the same secondary replica.

Routing groups will get rebalanced when Front End servers are added or removed from the pool. If the primary replica goes down another will be promoted to primary. Depending on both user count and how the primary became unavailable will dictate when the Windows Fabric rebuilds another replica. The replica knows the pools user count and if it decides creating another replica is too expensive of an operation it might wait 15-30 minutes. Also, if the primary server was taken down gracefully for patching (stop-cswindowsservice –graceful), Windows Fabric might wait longer than if the server crashed or was just powered off. We don’t have any control over how Windows Fabric handles these operations.

In regards to SBA and SBS as it pertains to routing groups each unit gets its OWN unique routing group (by design). Those would be in addition to the routing created for users homed on that pool. This means that if you have 3000 users on an SBS all of those users will have the same primary, secondary, and backup secondary replicas. The reason this is important is because this needs to be factored into a design when building out a highly available infrastructure that can support all Lync services.

 

Quorum Loss Recovery

If we lose all replicas within a routing group before Windows Fabric has a chance to rebuild more the replica set will go into quorum loss. When that routing group is in this type of quorum loss users will NOT be able to login. If 2 replicas are lost (1 remaining online) in a short period of time we will also go into quorum loss but users will be logged in with limited functionality mode (no contact list or presence but can still IM). The routing group will stay in that state until either the servers come back online or we manually run Reset-CsPoolRegistrarState with the QuorumLossRecovery option.  Remember these scenarios will not affect all users but only the users that were a part of that routing group.

You can verify the routing groups are functioning correctly by running the Get-CsPoolFabricState command (Figure 3). If there are routing groups in QuorumLoss you will see services that reference "no primaries" (Figure 4).

 

Figure 3: Get-CsPoolFabricState healthy

Figure 4: Get-CsPoolFabricState with routing groups in QuorumLoss

In order to recover from quorum loss you will need to run the Reset-CsPoolRegistrarState cmdlet with a –ResetType of QuorumLossRecovery (Figure 5).

Figure 5: Reset-CsPoolRegistrarState QuorumLossRecovery

The Reset-CsPoolRegistrarState cmdlet has multiple parameters which can be used for various changes to the cluster.

Reset-CsPoolRegistrarState –PoolFqdn <pool name fqdn> –ResetType {FullReset | QuorumLossRecovery | ServiceReset | MachineStateRemoved}

  • FullReset1 - cluster changes, any modification either bringing a pool into or out of 1-2 server pool, and changes to upgrade domains. In addition, this parameter rebuilds the local Lync Server databases. This type of reset can be potentially long and resource-intensive.
  • QuorumLossRecovery - Reloads user data from the backup store for any routing groups currently in quorum loss. (A quorum loss occurs when neither a database nor its replicas are available.) Data not yet written to the database could be lost when you do this type of reset.
  • ServiceReset1 - The RtcSrv and fabricHostSvc services are stopped and restarted. A service reset will be performed if the ResetType is not specified.
  • MachineStateRemoved - Removes the specified server from the pool. This type of reset should be used only when the server in question (or its databases) have been permanently lost.

1 Both the FullReset and ServiceReset will cause services to restart which will cause outages. This is why it's not a good idea to add front end servers to the pool during your production hours. When you add server it states you must restart front end services on all front ends in the pool.

To verify which replicas a user's data resides on we can run the Get-CsUserPoolInfo cmdlet (Figure 3). This is a useful command that will show us a ton of useful info about our registrars. If there aren't any servers listed then the users routing group might be in quorum loss.

Figure 6: Get-CsUserPoolInfo cmdlet

 

Upgrade Domains

Upgrade Domains are logical groupings of servers on which software maintenance such as upgrades and updates are performed at the same time. If you don’t adhere to upgrade domain guidelines for server patching, you will impact routing groups and potentially the pool itself. A routing group will never have two of its three servers in a single upgrade domain.

Depending on how many Front End servers are in a pool when it's created will dictate how many servers will be in each upgrade domain. The algorithm used to generate the upgrade domains is implemented by Topology Builder and can be viewed in the tbxml file after creating the topology. It is not supported to manually edit the tbxml file and change the upgrade domains. In general creating more servers in the pool will result in more servers per upgrade domain. This why it is critical to plan out your front ends in the design phase instead of adding servers here and there. If servers have to be added due to growth then there is nothing that can be done to decrease the amount of upgrade domains windows fabric creates.

So how do we monitor these upgrade domains and incorporate them into our patch process? We can use the Get-CsPoolUpgradeReadinessState cmdlet to display this data (Figure 4). There are a couple different upgrade domain states we might see which are listed below and how to handle each one.

  1. Busy – wait 10 minutes and check again. The fabric might still be balancing services which can cause this to read busy
  2. Busy 3x or InsufficientActiveFrontEnds1– there might be an insufficient amount of active front end servers in the pool or something is wrong with pool\upgrade domain. If this is the case check out Event Viewer to see what issues are occurring on these servers.
  3. Ready – Drain (Stop-CsWindowsService), Patch, and then reboot the server

After you have rebooted the server, just wait a couple of minutes before running the Get-CsPoolUpgradeReadinessState cmdlet again to find out if the pool is ready to take another upgrade domain down. Remember you should only patch ONE upgrade domain at a time.

1 If your front end pool only has 1 servers you will always get InsufficientActiveFrontEnds. In this case you know there will be an outage so you can just patch and restart that server.

 

Figure 7: Get-CsPoolUpgradeReadinessState with expanded properties

 

Best Practices "Amount of Servers in Pool"

Our recommendation is to build pools with a minimum of 3 servers. Although we support 2 server pools there are considerations with this configuration which everyone should be aware of.

  • The first issue is centered on how servers are rebooted and patched. If you following our best practice recommendation (http://technet.microsoft.com/en-us/library/gg412996.aspx) for patching it states both front end servers should be rebooted at the same time. If at any time both servers are taken offline at the same time you must bring them up in reverse order. In other works if you reboot server 1 then server 2 you must bring server 2 back up FIRST. The reason for this is because server 2 would be the last node to write quorum info to the backend and the cluster would not make quorum unless he was started first. If reverse order is not possible, use the Reset-CsPoolRegistrarState cmdlet with the QuorumLossRecovery parameter we discussed above.
  • Also keep in mind the fact that you will only have 2 copies of your data (Primary and Secondary).

 
 Troubleshooting Service Startup

  • If a routing group is down, RtCSrv will not start. (32169 - Server startup is being delayed because fabric pool manager is initializing). Use Reset-CsPoolRegistrarState cmdlet with the QuorumLossRecovery parameter
  • If a pool has gone down and stopped services, it requires 85% of servers to start back up.

 

SQL Queries

List Routings Group Names, Users in those groups, and the primary server for each routing group ordered by home server (Figure 5). This should be run against a front end server rtclocal sql instance dbo.Resource table.

Select FrontEnd.Fqdn, RoutingGroupAssignment.RoutingGroupName, Resource.UserAtHost

From ResourceDirectory

INNER JOIN Resource

ON ResourceDirectory.ResourceId=Resource.ResourceId

INNER JOIN RoutingGroupAssignment

ON ResourceDirectory.RoutingGroupId=RoutingGroupAssignment.RoutingGroupId

INNER JOIN FrontEnd

ON RoutingGroupAssignment.FrontEndId=FrontEnd.FrontEndId

ORDER BY FrontEnd.Fqdn

 

Figure 8: SQL query to list routing groups, primary server, and users

Thanks to both Bryan Nyce and Daniel Hernandez for helping document this popular technical information request. Also thanks to Tommy Mhire for providing some of this excellent material.

Read the original blog entry...

More Stories By Richard Schwendiman

My name is Richard Schwendiman and I am currently working for Microsoft as a (PFE) Premier Field Engineer specializing in both Exchange and Lync. I have been working as an IT Consultant for 13+ years focusing on a wide array of Infrastructure technologies. These technologies include Messaging, UC, Networking, Platforms, Active Directory, Virtualization, etc... I am currently certified as an MCSE (Microsoft Certified Systems Engineer), MCSE Messaging 2013, MCSE Communications 2013, MCSA 2012, MCITP Enterprise Messaging, MCTS-Lync, CCNA (Cisco Certified Network Associate), Commvault, CCNP (Cisco Certified Network Professional), and JNCIA-ER (Juniper Enterprise Routing). I am hoping that through this blog I can bring knowledge from the field and keep everyone informed about our ever changing Industry. Please feel free to email me any questions, comments, or concerns pertaining to this blog or any technology related things. Thanks and look forward to providing some good content. http://blogs.technet.com/b/rischwen/

@CloudExpo Stories
The speed of software changes in growing and large scale rapid-paced DevOps environments presents a challenge for continuous testing. Many organizations struggle to get this right. Practices that work for small scale continuous testing may not be sufficient as the requirements grow. In his session at DevOps Summit, Marc Hornbeek, Sr. Solutions Architect of DevOps continuous test solutions at Spirent Communications, will explain the best practices of continuous testing at high scale, which is r...
Modern Systems announced completion of a successful project with its new Rapid Program Modernization (eavRPMa"c) software. The eavRPMa"c technology architecturally transforms legacy applications, enabling faster feature development and reducing time-to-market for critical software updates. Working with Modern Systems, the University of California at Santa Barbara (UCSB) leveraged eavRPMa"c to transform its Student Information System from Software AG's Natural syntax to a modern application lev...
Plutora provides enterprise release management and test environment SaaS solutions to clients in North America, Europe and Asia Pacific. Leading companies across a variety of industries, including financial services, telecommunications, retail, pharmaceutical and media, rely on Plutora's SaaS solutions to orchestrate releases and environments faster and with integrity. Products include Plutora Release Manager, Plutora Test Environment Manager and Plutora Deployment Manager.
Hosted PaaS providers have given independent developers and startups huge advantages in efficiency and reduced time-to-market over their more process-bound counterparts in enterprises. Software frameworks are now available that allow enterprise IT departments to provide these same advantages for developers in their own organization. In his workshop session at DevOps Summit, Troy Topnik, ActiveState’s Technical Product Manager, will show how on-prem or cloud-hosted Private PaaS can enable organ...
The world's leading Cloud event, Cloud Expo has launched Microservices Journal on the SYS-CON.com portal, featuring over 19,000 original articles, news stories, features, and blog entries. DevOps Journal is focused on this critical enterprise IT topic in the world of cloud computing. Microservices Journal offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. Follow new article posts on T...
When it comes to building applications, one database definitely does not fit all. Traditional SQL databases are great for storing highly structured, normalized data and performing analytics and reporting. NoSQL has attracted developers with its awesome flexibility, and JSON-centric document stores like Cloudant make web developers incredibly productive by offering a JavaScript environment from end-to-end. Recent Big Data challenges have driven the need for a distributed approach to analytics e...
SYS-CON Events announced today the IoT Bootcamp – Jumpstart Your IoT Strategy, being held June 9–10, 2015, in conjunction with 16th Cloud Expo and Internet of @ThingsExpo at the Javits Center in New York City. This is your chance to jumpstart your IoT strategy. Combined with real-world scenarios and use cases, the IoT Bootcamp is not just based on presentations but includes hands-on demos and walkthroughs. We will introduce you to a variety of Do-It-Yourself IoT platforms including Arduino, Ras...
SYS-CON Events announced today that SafeLogic has been named “Bag Sponsor” of SYS-CON's 16th International Cloud Expo® New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. SafeLogic provides security products for applications in mobile and server/appliance environments. SafeLogic’s flagship product CryptoComply is a FIPS 140-2 validated cryptographic engine designed to secure data on servers, workstations, appliances, mobile devices, and in the Cloud....
SYS-CON Events announced today that the DevOps Institute has been named “Association Sponsor” of SYS-CON's DevOps Summit, which will take place on June 9–11, 2015, at the Javits Center in New York City, NY. The DevOps Institute provides enterprise level training and certification. Working with thought leaders from the DevOps community, the IT Service Management field and the IT training market, the DevOps Institute is setting the standard in quality for DevOps education and training.
Even though it’s now Microservices Journal, long-time fans of SOA World Magazine can take comfort in the fact that the URL – soa.sys-con.com – remains unchanged. And that’s no mistake, as microservices are really nothing more than a new and improved take on the Service-Oriented Architecture (SOA) best practices we struggled to hammer out over the last decade. Skeptics, however, might say that this change is nothing more than an exercise in buzzword-hopping. SOA is passé, and now that people are ...
SYS-CON Events announced today the DevOps Foundation Certification Course, being held June ?, 2015, in conjunction with DevOps Summit and 16th Cloud Expo at the Javits Center in New York City, NY. This sixteen (16) hour course provides an introduction to DevOps – the cultural and professional movement that stresses communication, collaboration, integration and automation in order to improve the flow of work between software developers and IT operations professionals. Improved workflows will res...
Containers and microservices have become topics of intense interest throughout the cloud developer and enterprise IT communities. Accordingly, attendees at the upcoming 16th Cloud Expo at the Javits Center in New York June 9-11 will find fresh new content in a new track called PaaS | Containers & Microservices Containers are not being considered for the first time by the cloud community, but a current era of re-consideration has pushed them to the top of the cloud agenda. With the launch ...
The WebRTC Summit 2014 New York, to be held June 9-11, 2015, at the Javits Center in New York, NY, announces that its Call for Papers is open. Topics include all aspects of improving IT delivery by eliminating waste through automated business models leveraging cloud technologies. WebRTC Summit is co-located with 16th International Cloud Expo, @ThingsExpo, Big Data Expo, and DevOps Summit.
SOA Software has changed its name to Akana. With roots in Web Services and SOA Governance, Akana has established itself as a leader in API Management and is expanding into cloud integration as an alternative to the traditional heavyweight enterprise service bus (ESB). The company recently announced that it achieved more than 90% year-over-year growth. As Akana, the company now addresses the evolution and diversification of SOA, unifying security, management, and DevOps across SOA, APIs, microser...
The webinar, hosted by XebiaLabs, will feature 4 experts including Special Host Gene Kim, author of The Phoenix Project, along with IT thought leaders Gary Gruver, Randy Shoup and XebiaLabs' Andrew Phillips. The panel brings more than 30 years of collective experience surrounding microservices transformations at major companies including Google, eBay and Tripwire. "The story around microservices and containers is pretty compelling and the attraction of more flexibility is obviously alluring,"...
SYS-CON Events announced today that Creative Business Solutions will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Creative Business Solutions is the top stocking authorized HP Renew Distributor in the U.S. Based out of Long Island, NY, Creative Business Solutions offers a one-stop shop for a diverse range of products including Proliant, Blade and Industry Standard Servers, Networking, Server Options and...
SYS-CON Events announced today that FierceDevOps will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. FierceDevOps keeps software developers and IT operations personnel updated on the latest news and trends around the rapidly evolving role of the traditional IT worker.
GENBAND has announced that SageNet is leveraging the Nuvia platform to deliver Unified Communications as a Service (UCaaS) to its large base of retail and enterprise customers. Nuvia’s cloud-based solution provides SageNet’s customers with a full suite of business communications and collaboration tools. Two large national SageNet retail customers have recently signed up to deploy the Nuvia platform and the company will continue to sell the service to new and existing customers. Nuvia’s capabili...
WHOA.com has announced the newest addition to its data center footprint with the expansion into Equinix's newest state-of-the-art facility: DC-11 Washington, DC IBX+. Located in Ashburn, VA, this data center expands Whoa.com's presence to meet rapidly expanding customer demand for secure cloud solutions. Equinix, Inc. operates International Business Exchange™ (IBX®) data centers in 32 markets across 15 countries in the Americas, EMEA, and Asia-Pacific. Equinix is committed to operating faciliti...
SYS-CON Media announced today that @WebRTCSummit Blog, the largest WebRTC resource in the world, has been launched. @WebRTCSummit Blog offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. @WebRTCSummit Blog can be bookmarked ▸ Here @WebRTCSummit conference site can be bookmarked ▸ Here