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Download as PDF, TXT or read online from Scribd VMware vSphere Clustering Deepdive Copyrights About the Authors Acknowledgements “ VMware vSphere HA and DRS technical Deepdive” and best seller “VMware vSphere. Clustering Deepdive with and who designed all the great diagrams which you find throughout this my technical conscious: Keith Farkas, Cormac Hogan, Manoj Krishnan, Anne Holler,. Mustafa Uysal PDF - ePub - Mobi. The source of VMware engineered a feature called VMware vSphere High Availability. VMware. VMware Inc. All rights reserved. VMware vSphere vCenter Server - Technical Deep Dive. Scott Calvet – Technical Account Executive – VCP-DV 5.
Click URL instructions: A failure occurred when failing over a virtual machine. Partially automated: It is useful for automated document creation. What is HA Admission Control about?
The host that is participating in the election with the greatest number of connected datastores will be elected. This means that it will not only receive but also send information to vCenter when required.
The HA master is also the host that initiates the restart of virtual machines when a host has failed. A master election thus occurs when HA is first enabled on a cluster and when the host on which the master is running: TCP connection to the master.
One thing to stress here though is that slaves do not communicate with each other after the master has been elected unless a re-election of the master needs to take place. After a master is elected. This includes the role as depicted in Figure 7 where the host is a master host. The master distributes this inventory across all datastores in use by the. The master will also attempt to take ownership of any datastores it discovers along the way. This however is done lexically.
For each host. This secure connection is SSLbased. The naming format and location of this file is as follows: Calling it an inventory might be slightly overstating: It keeps track of which virtual machines are protected by HA. Figure 7: Master Agent As stated earlier. If two or more hosts have the same number of datastores connected.
Figure 8: Protectedlist file Now that we know the master locks a file on the datastore and that this file stores inventory details. In a scenario like this. This new master will read the required information and will initiate the restart of the virtual machines within roughly 10 seconds. In the case of isolation. If the master fails. If the slaves have received no network heartbeats from the master. There is more to this process but we will discuss that in Chapter 4.
If a slave fails or becomes isolated from the management network. It is also responsible for monitoring the state of the slave hosts and reporting this state to vCenter Server. What will happen and how do the slaves know that the master has failed? The master will release the lock it has on the file on the datastore to ensure that when a new master is elected it can determine the set of virtual machines that are protected by HA by reading the file. Restarting virtual machines is not the only responsibility of the master.
Figure 8 shows an example of this file on one of the datastores. The slave also monitors the health of the master by monitoring heartbeats. All of these responsibilities are really important. We will now discuss the files that are created by both the master and the slaves. Just like the slaves receive heartbeats from the master. It uses a placement engine that will try to distribute the virtual machines to be restarted evenly across all available hosts.
Last but not least. Like the master to slave communication. Figure 9: Slave Agent Files for both Slave and Master Both the master and slave use files not only to store state. When virtual machines need to be restarted. Remote files are files stored on a shared datastore and local files are files that are stored in a location only directly accessible to that host.
If the master becomes unavailable. HA does not use multicast. Remote Files. Slaves A slave has substantially fewer responsibilities than a master: Figure Locally stored files Each host.
See Figure 8 for an example of these files. This file is not human-readable. Although we expect that most of you will never touch these files — and we highly recommend against modifying them — we do want to explain how they are used: It should be noted that. It contains the actual compatibility info matrix for every HA protected virtual machine and.
Local Files As mentioned before. This file is also used by the slaves to inform the master that it is isolated from the management network: This information is persisted locally on each host. The data that is locally stored is important state information. A 0 means not-isolated and a 1 means isolated. Updates to this information is sent to the master by vCenter and propagated by the master to the slaves. The master will inform vCenter about the isolation of the host.
The naming scheme for this file is as follows: It contains the configuration details of the cluster. Ensure the management network is highly resilient to enable proper state determination. Datastore heartbeating adds a new level of resiliency and prevents unnecessary restart attempts from occurring.
For instance. As you can imagine. This file contains the configuration settings around logging. Network Heartbeating vSphere 5. A list of hosts participating in the cluster. Basic design principle Network heartbeating is key for determining the state of a host. Heartbeating We mentioned it a couple of times already in this chapter.
The new datastore heartbeat mechanism is only. This has been mitigated by the introduction of the datastore heartbeating mechanism. Heartbeating is the mechanism used by HA to validate whether a host is alive. IP addresses. These heartbeats are sent by default every second. With the introduction of vSphere 5. Datastore heartbeating enables a master to more correctly determine the state of a host that is not reachable via the management network.
MAC addresses and heartbeat datastores. This scenario is described in-depth in Part IV of this book. This however is not a guarantee that vCenter can select datastores which are connected to all hosts. In scenarios where hosts are geographically dispersed it is recommend to manually select heartbeat datastores to ensure each site has one site-local heartbeat datastore at minimum.
It is recommended to manually select site local datastores. If the master determines that the slave is Isolated or Partitioned. Selecting the heartbeat datastores.
It should be noted that vCenter is not site-aware. Let that be clear! Based on the results of checks of both files. Although it is possible to configure an advanced setting das. HA selects 2 heartbeat datastores — it will select datastores that are available on all hosts.
If the master determines that a host has failed no datastore heartbeats. If desired. By default. This for instance shows you which datastores are being used for heartbeating and which hosts are using which specific datastore s. The question now arises: Validating the heartbeat datastores How does this heartbeating mechanism work?
HA ensures there is at least one file open on this volume by creating a file specifically for datastore heartbeating. In order to update a datastore heartbeat region. Basic design principle Datastore heartbeating adds a new level of resiliency but is not the be-all end-all. HA will simply check whether the heartbeat region has been updated.
The master will simply validate this by checking that the time-stamp of the file changed. In converged networking environments. Isolated versus Partitioned. HA will detect this and select a new datastore or NFS share to use for the heartbeating mechanism.
Heartbeat file On NFS datastores. In other words. Realize that in the case of a converged network environment. On VMFS datastores. It is possible for multiple hosts to be isolated at the same time. We call the set of hosts that are partitioned but can communicate with each other a management network partition. Two hosts are considered partitioned if they are operational but cannot reach each other over the management network. Figure 14 shows possible ways in which an Isolation or a Partition can occur.
Network partitions involving more than two partitions are possible but not likely. What is this exactly and when is a host Partitioned rather than Isolated? Before we will explain this we want to point out that there is the state as reported by the master and the state as observed by an administrator and the characteristics these have.
When any FDMs are not in network contact with a master. In the HA architecture. It should be noted that a master could claim responsibility for a virtual machine that lives in a different partition. The master cannot alone differentiate between these two states — a host is reported as isolated only if the host informs the master via the datastores that is isolated.
If this occurs and the virtual machine happens to fail. When the network partition is corrected. If a cluster is partitioned in multiple segments. When a partition occurs. When the master stops receiving network heartbeats from a slave. If both are negative. When the host is marked as Failed. Before the host is declared failed.
To reiterate. HA will trigger an action based on the state of the host. If the host does not have access to the datastore. If it can. As mentioned earlier. When the host is marked as Isolated. The one thing to keep in mind when it comes to isolation response is that a virtual machine will only be shut down or powered off when the isolated host knows there is a master out there that has taken ownership for the virtual machine or when the isolated host loses access to the home datastore of the virtual machine.
If no master owns the datastores. We do want to stress that this only applies to protecting virtual machines. When the state of a virtual machine changes. When the power state change of a virtual machine has been committed to disk. If the term isolation response is not clear yet. We have explained this briefly but want to expand on it a bit more to make sure everyone understands the dependency on vCenter when it comes to protecting virtual machines.
Virtual Machine Protection The way virtual machines are protected has changed substantially in vSphere 5. The reason for this. As pointed out earlier. Virtual Machine protection workflow. To clarify the process. Virtual Machine Unprotection workflow. We have documented this workflow in Figure 16 for the situation where the power off is invoked from vCenter. A good example of an agent virtual machine is a vShield Endpoint virtual machine which offers antivirus services.
Chapter 4 Restarting Virtual Machines In the previous chapter. HA will still take the configured priority of the virtual machine into account.
There are multiple scenarios in which HA will respond to a virtual machine failure. HA would take the priority of the virtual machine into account when a restart of multiple virtual machines was required.
Restart Priority and Order Prior to vSphere 5. Agent Virtual Machines. Reliability of HA in this case mostly refers to restarting or resetting virtual machines. HA will respond when the state of a host has changed. Before we dive into the different failure scenarios. Changing the process results in slightly different recovery timelines.
We have shown you that multiple mechanisms were introduced in vSphere 5. These agent virtual machines are considered top priority virtual machines.
These apply to every situation we will describe. There are many different scenarios and there is no point in covering all of them. In the meantime. HA would keep retrying forever which could lead to serious problems. Restart Retries The number of retries is configurable as of vCenter 2. Keep in mind that some virtual machines might be dependent on the agent virtual machines. Prior to vCenter 2. We have listed the full order in which virtual machines will be restarted below: HA also prioritizes FT secondary machines.
The default value is 5. If the restart of a top priority virtual machine fails. Now that we have briefly touched on it. Besides agent virtual machines. Prioritization is done by each host and not globally. Each host that has been requested to initiate restart attempts will attempt to restart all top priority virtual machines before attempting to start any other virtual machines.
Basic design principle Virtual machines can be dependent on the availability of agent virtual machines or other virtual machines. You should document which virtual machines are dependent on which agent virtual machines and document the process to start up these services in the right order in the case the automatic restart of an agent virtual machine fails.
This scenario is described in KB article where multiple virtual machines would be registered on multiple hosts simultaneously. Although HA will do its best to ensure all virtual machines are started in the correct order.
Document the proper recovery process. HA will continue powering on the remaining virtual machines. Note Prior to vSphere 5. There are specific times associated with each of these attempts.
As said. HA will try to start the virtual machine on one of your hosts in the affected cluster. The following bullet list will clarify this concept. The elapsed time between the failure of the virtual machine and the restart.
Before we go into the exact timeline. This by itself could be 30 seconds after the virtual machine has failed. Meaning that the total amount of restarts was 6. High Availability restart timeline. As clearly depicted in Figure The 33rd power on attempt will only be initiated when one of those 32 attempts has completed regardless of success or failure of one of those attempts.
In theory. When it comes to restarts. T2 could be T2 plus 8 seconds. HA will start the 2-minute wait as soon as it has detected that the initial attempt has failed.
To make that more clear. The master. The restart priority however does guarantee that when a placement is done. Let it be absolutely clear that HA does not wait to restart the low-priority virtual machines until the high-priority virtual machines are started. Another important fact that we want emphasize is that there is no coordination between masters. Although only one will succeed. If there are 32 low-priority virtual machines to be powered on and a single high-priority virtual machine.
Be aware. In most environments. Keeping in mind that this is an actual failure of the host. Just in case it happens. T18s — If heartbeat datastores are configured. This is a continuous ping for 5 seconds.
We want to emphasize this because the time it takes before a restart attempt is initiated differs between these two scenarios.
T3s — Master begins monitoring datastore heartbeats for 15 seconds. Now that we know how virtual machine restart priority and restart retries are handled. T10s — The host is declared unreachable and the master will ping the management network of the failed host.
There is a clear distinction between the failure of a master versus the failure of a slave. T15s — If no heartbeat datastores are configured. Basic design principle Configuring restart priority of a virtual machine is not a guarantee that virtual machines will actually be restarted in this order.
Part of this complexity comes from the introduction of a new heartbeat mechanism. Ensure proper operational procedures are in place for restarting services or virtual machines in the appropriate order in the event of a failure.
If heartbeat datastores have been configured. The master will also start pinging the management network of the failed host at the 10th second and it will do so for 5 seconds.
On the 10th second T10s. Restart timeline slave failure. When the slave fails. The master monitors the network heartbeats of a slave. If no heartbeat datastores were configured. We realize that this can be confusing and hope the timeline depicted in Figure 18 makes it easier to digest. We have defined this as T0. After 3 seconds T3s. As an example. If the master did not know the on-disk protection state for the virtual machine. If there is a network partition multiple masters could try to restart the same virtual machine as vCenter Server also provided the necessary details for a restart.
The master filters the virtual machines it thinks failed before initiating restarts. In this. T25s — New master elected and reads the protectedlist. Restart timeline master failure. This change in behavior was introduced to avoid the scenario where a restart of a virtual machine would fail due to insufficient resources in the partition which was responsible for the virtual machine. The timeline is as follows: At T25s. This means that an election will need to take place amongst the slaves.
The reason being that there needs to be a master before any restart can be initiated.
The Failure of a Master In the case of a master failure. That leaves us with the question of what happens in the case of the failure of a master. With this change. The election process takes 15s to complete. Slaves receive network heartbeats from their master. This list contains all the virtual machines which are protected by HA. T10s — Master election process initiated.
T35s — New master initiates restarts for all virtual machines on the protectedlist which are not running. As every cluster needs a master. The timeline depicted in Figure 19 hopefully clarifies the process.
At T35s. Isolation Response and Detection Before we will discuss the timeline and the process around the restart of virtual machines after an isolation event.
Besides the failure of a host. Keep in mind that these changes are only applicable to newly created clusters. There was a lot of feedback. Cluster default settings The default setting for the isolation response has changed multiple times over the last couple of years and this has caused some confusion.
When upgrading an existing cluster. It is a hard stop. This setting can be changed on the cluster settings under virtual machine options Figure If VMware Tools is not installed. When creating a new cluster. Shut down — When isolation occurs. This time out value can be adjusted by setting the advanced option das. This does not necessarily mean that the whole network is down. You might wonder why the default has changed once again. Leave powered on — When isolation occurs on the host.
Today there are three isolation responses: This isolation response answers the question. If this is not successful within 5 minutes. The obvious answer applies here. Of course. HA will validate if virtual machines restarts can be attempted — there is no reason to incur any down time unless absolutely necessary. In a converged network environment with iSCSI storage. Basically resulting in the power off or shutdown of every single virtual machine and none being restarted.
It is still difficult to decide which isolation response should be used. We feel that changing the isolation response is most useful in environments where a failure of the management network is likely correlated with a failure of the virtual machine network s. Basic design principle Before upgrading an environment to later versions. One of the problems that people have experienced in the past is that HA triggered its isolation response when the full management network went down.
The question remains. It does this by validating that a master owns the datastore the virtual machine is stored on. The following table was created to provide some more guidelines. Document them. That is no longer the case with vSphere 5. HA did not care and would always try to restart the virtual machines according to the last known state of the host.
Before the isolation response is triggered. The master will recognize that the virtual machines have disappeared and initiate a restart. When isolation response is triggered. Meaning that if a single ping is successful or the host observes election traffic and is elected a master or slave.
When a host has declared itself isolated and observes election traffic it will declare itself no longer isolated. In this timeline. This delay can be increased using the advanced option: The mechanism is fairly straightforward and works with heartbeats. There are. The following timeline is the timeline for a vSphere 5. The main difference is the fact that HA triggers a master election process before it will declare a host is isolated. Isolation of a Slave The isolation detection mechanism has changed substantially since previous versions of vSphere.
Isolation Detection We have explained what the options are to respond to an isolation event and what happens when the selected response is triggered. Isolation of a slave timeline Isolation of a Master In the case of the isolation of a master.
After the completion of this sequence. These power-off files are deleted when a virtual machine is powered back on or HA is disabled. The power-off file is used to record that HA powered off the virtual machine and so HA should restart it.
A secondary management network will more than likely be on a different subnet and it is recommended to specify an additional isolation address which is part of the subnet. We recommend setting an additional isolation address. Figure 22 Figure Isolation Address Selecting an Additional Isolation Address A question asked by many people is which address should be specified for this additional isolation verification. Failure Detection Time Those who are familiar with vSphere 4.
HA gives you the option to define one or multiple additional isolation addresses using an advanced setting. Basic design principle Select a reliable secondary isolation address. If required. Another usual suspect would be a router or any other reliable and pingable device on the same subnet.
If a secondary management network is configured. This advanced setting is called das. We generally recommend an isolation address close to the hosts to avoid too many network hops and an address that would correlate with the liveness of the virtual machine network.
In many cases. If the master is not in contact with vCenter Server or has not locked the file. When the master node declares the slave node as Partitioned or Isolated. Restarting Virtual Machines The most important procedure has not yet been explained: At this point. If the host was not Partitioned or Isolated before the failure. We have explained the difference in behavior from a timing perspective for restarting virtual machines in the case of a both master node and slave node failures.
The minimum value is These files are asynchronously read approximately every 30s. Now that HA knows which virtual machines it should restart. This setting was completely removed when HA was rewritten. In almost all scenarios 30 seconds should suffice. Before it will initiate the restart attempts. For now. This validation uses the protection information vCenter Server provides to each master. We do not recommend changing this advanced setting unless there is a specific requirement to do so.
We have dedicated a full section to this concept as. Extensions can improve your productivity, and are easy to use. You seem to have CSS turned off.
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