vCenter Server High Availability

[Music] [Music] hi my name is Adam a curly I'm a senior technical marketing architect with VMware and the cloud platform business unit today we're going to talk about vCenter high availability a couple of things to know before we get started first vCenter h.a is comprised of three nodes and active a passive and a witness another common question is what licensing is involved well we just require a single vCenter server instance license that will cover all three nodes another common question is do we support a tiny deployment which is the smallest size that you can select when you're deploying a vCenter server and the answer is we do not support that with vCenter HHA because of the resources that are involved tiny is usually used for lab environments and very small Robo instances so we recommend or require at least a small or higher deployment we also support embedded PSC and external PSC with vCenter H a and last does V Center high-availability equal D are definitely not we'll get into some of the details of that and the ramifications and the decisions that you need to make when enabling v CH a but V center high availability is just an H H solution we want to protect V Center and make it highly resilient within a site generally speaking so the first thing that we need to do from an architecture perspective is take these clones right we have an active and we clone that over to a passive node and we also clone a third or second time to a witness node one thing that we do before we actually initiate the clones is we add a second Ethernet adapter and this is this course is of course cloned to the witness and passive mode we also have our primary Ethernet adapter or Ethernet zero which is made up of we'll call it the management interface and it's comprised of an fqdn and IP and a MAC address then we also have this interface over on our passive node I'm drawing it in a dashed line because it is administratively offline right if this interface shares both the IP and MAC address then we'll have some network conflicts if both of these interfaces are online at the same time so on the passive node this Ethernet zero or the management interface is always offline only when the passive node becomes the active node does it become online and take over the IP and MAC address and we'll talk a little bit more about that in detail in a moment so these Ethernet 1 interfaces form a private network we call the V CH a network the only requirements for this network are that it is different from the management Network and that all three nodes can have IP addresses and communicate over this network it can be over layer three we don't require all three of these nodes to have layer two connectivity across the VCH a network however again ten is going back to the VCH a is not BR there's very limited scenarios where you might have a requirement to have these three nodes be on different networks so generally speaking these three nodes will be on the same layer two segments although it is not required now that we have the network situated there are a few other things that make up a V Center right we have a database and then we have some set of files on the file system that make up the configuration configuration files certificates things of that nature and so we need to get these two things these two sets of data over to our passive node so there's going to be some replication involved first we have the database replication this is a synchronous replication operation we're just using the native post great sequel replication mechanisms to get the data from point A to point B or from the active node to the passive mode the other is a file based asynchronous mechanism that actually uses a very mature Linux based synchronous synchronization mechanism called our sink our sink is an on-demand replication mechanism that we're using and the files that we're replicating are generally pretty small so usually even though it's asynchronous it takes just a matter of seconds to replicate a change from active to passive node when that change occurs so now we've kind of dobe into the architecture of vCenter a che let's take a look at what happens when we have a failure so let's say that our active node has some sort of failure maybe the host failed on it or maybe there is a network failure or some sort and so this guy goes away so now what we're going to do is we're going to bring this interface online we're going to do a gratuitous ARP to notify the network that now this passive node or now as it were the new active node has taken ownership of the fqdn IP and MAC address okay so now this interface is effectively down and the other thing is that replication is now paused if you will right we have a one-way replication now that the active node is down and the passive node has become the active replication vCenter is online but replication is now paused so now we have a couple of choices one we can trouble go ahead and troubleshoot the failed active node and if we can successfully troubleshoot it and bring it back online then the passive node as soon as it detects or the active node as soon as it detects the passive node online it will reestablish those replication mechanisms so now we'll do our synchronous database replication this way and our asynchronous file based replication that way as well there's another option that we can take if we have a failed node when V Center is back online after the failover if for instance we're unable to successfully troubleshoot the problem we can go into the V Center H a configuration and choose to redeploy the node so this can happen completely non disruptively if our if our old active node our original V Center node is completely just blown away we can remove it from inventory and then into the UI and select to redeploy this node and it will come up perform an initial synchronization of the database in the file system and then it will become the new passive node and again this is all non-disruptive there's a couple other failure conditions to really talk about one is what if we lose the witness now the witness doesn't fit in the data path it is just used for quorum services so if we lose the witness it's going to be non disruptive to the vCenter server instance but now the cluster is running in a degraded State so all three nodes need to be online and functioning for the cluster to be healthy if we lose one of the nodes whether it's a passive node or a witness node that cluster goes into a degraded state when the cluster is in that degraded state we're not able to perform an automatic failover from active to passive this is a normal mechanism that many clusters solutions use and is really to prevent two actives to come online at the same time so we talked about this these two network interfaces and what would happen if they would come online at the same time that's what we're trying to prevent so if there is network isolation and the VCH a network preventing these nodes from talking to each other V Center will actually shut down the center services to protect itself and again that only occurs when we have two or more nodes that I've failed so this architecture lends itself to an embedded PSC itok that we support both embedded in external PFC and if we're talking about embedded PSC just know that the embedded PSC runs on the active node and again we've cloned it so it's running on both the active in the passive node and it's a single instance of a PSC it's not actually two separate instances that are replicating to each other the vCenter H a replication mechanism is what is taking taking care of B to PFC s being able to share the same information so when there's a failover that occurs the other embedded PSD comes online along with vCenter server itself and everything is working normally what about if we have an external PFC so there's a very important decision that you need to make when talking about PSP and vCenter h.a are you going to use enhanced link mode if the answer is yes then Union vSphere 6.5 you have to use an external PFC we do not support embedded PSC replication at this time so if I have a few external PFC s here because I want enhanced link mode I'll draw my B Center we also require you to have a load balancer the reason for this is if I have my highly available PSC conserved v center configuration here where I have an active a passive and a witness this v center is could potentially be pointed to a specific PFC now if we were to have a failure then if let's say this PSC failed then we would need to manually repoint this v center over to another PSC when we do that that repoint mechanism does not replicate to the passive node so the passive node is still pointed to this original PSC and so you can see if we had a failure of a V Center node and failed over to the passive node then we would have a problem because the passive node is still pointing over to the failed PSC so this is why the load balancer becomes very important when we're talking about high availability one of the questions that I raised often is why make the V Center highly available but not the platform services controller if we can make both layers highly available then we have a complete solution otherwise we're providing a resiliency envy center H a but then having to do some manual intervention which contradicts the high availability principle if we were to have a PFC failure so the ideal scenario is if we're using enhanced link mode and thus using external pscs in conjunction with V Center H a we need to have these two PFC s behind a load balancer with the V centers pointed at this virtual IP or VIP on the load balancer that concludes this whiteboard session on V Center high availability you can find more information on the vSphere blog at blogs and we're calm slash vSphere [Applause] [Music] you

Channel: VMware vSphere

Views: 48,704

Keywords: vSphere, vCenter Server, high availability, vsphere, vmware, esxi

Id: Z8VeYMxcSBM

Length: 13min 26sec (806 seconds)

Published: Tue Mar 14 2017

Reddit Comments

[u/The_Packeteer]

Thanks for sharing this.

I have customers asking about vCenter HA regularly. This will be nice to watch with them prior to me giving them the rundown.

[u/Lefty4444]

Awesome video, white/glassboard skills and explaination! Please make more!

[u/Yamaha_User]

I'm impressed by all the backwards writing. Thats quite a skill :)

[u/tomsonxxx]

Very good way for explaining features.

Is VCHA also useful for Maintenance of VCSA without downtime? Ex. you give over to your second/failover instance, patch the primary instance and make a giveback?