In previous tips in this series on high availability HA in the data center, you've read how resume title for fresh graduate set up a Linux HA infrastructure. The only requirement is that the environment needs to have shared storage. Typically, that would be a storage area network SAN. If something goes wrong with a node in the cluster, a poison pill is written for that node to the shared storage device.
Your Linux cluster is now in a safe state, so you can start creating the resources you want to protect with HA. In the next tip in this series, you'll learn how to set up Apache for Linux HA. About the expert:Sander van Vugt is an independent trainer and consultant living in the Netherlands.
Van Vugt is an expert in Linux high availability, virtualization and performance, and has completed several projects that implement all three. Sander is also a regular speaker on many Linux conferences all over the world. Please check the box if you want to proceed.
The traditional Microsoft Office applications you get from Office might appear to be the same on the surface, but how you Does your current Active Directory permissions setup spark joy? If not, then it's time to unscramble that confusing design into Configuring advanced VM settings is no easy task. Some common questions admins ask include where to place VM swap files and how Log files generate vast amounts of data, which negatively affects performance.
As a result, admins should build logging Learn how AWS Lambda has been updated over the years to address shortcomings in its serverless computing platform, and how Let's take a look at on-premises vs. Many factors go into managing Azure resources, and they vary based on a company's needs.
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Configure advanced VM settings in vSphere 6. Employ log management best practices to better analyze, protect data Log files generate vast amounts of data, which negatively affects performance. Evaluate on-premises vs.It also helps to bring the cluster into the known state when there is a split brain occurs between the nodes.
This reporting works well until communication breaks between the nodes. Majority of nodes will form the cluster based on quorum votes and rest of the nodes will be rebooted or halted based on fencing actions what we have denied.
Using the resource level fencing, the cluster can make sure that a node cannot access same resources on both the nodes. The node level fencing makes sure that a node does not run any resources at all. This is usually done in a very simple, yet brutal way: the node is simply reset using a power switch.
This may ultimately be necessary because the node may not be responsive at all. For more informationplease visit clusterlabs. Here we will see the node level fencing. Make sure that you are proving the correct interface as the bridge.
Cluster has been configured between two KVM guests. Worth to add here that in such config fence will work correctly only if VM name on KVM is the same as cluster node name in cluster configuration. How to allow br0 interface packet to broadcast to other nodes.
How do we configure two fencing devices with pacemaker, incase Node 1 is physical and Node2 is virtual? In my case how changes the tutorial? Your email address will not be published.
Related Articles. Leave a Reply Cancel reply Your email address will not be published.One of the key requirements of Pacemaker is that there must be good communication between the nodes at all times. This is so that the cluster is always aware of what is going on, and can ensure that resources are properly managed.
When nodes in a cluster begin to operate independently from one another, the situation is known as a split-brainand each node or collection of nodes in this situation is known as a sub-cluster.
You can do your best to mitigate this by ensuring you have 2 independent routes of communication and independent here means ideally physically separate wires, switches etc. However, whatever methods you use to ensure connectivity, there will always be one fateful day when for some reason communication with one or more nodes is lost, or corruption on a node causes it to start behaving erratically. At this point you need to have previously set up fencing. If you have 3 or more nodes in a pool, and 1 of them starts behaving erratically, the majority can decide amongst themselves that the other node should be dealt with.
Of course, quorum by its very definition requires more than 2 nodes. So, to start with lets assume you have 3 or more nodes. Here, using quorum is easy. Whenever quorum is present, pacemaker will go with the majority vote on important decisions. When quroum is lost i. So, lets assume you have quorum set up with enough nodes, and suddenly one node disappears out of the cluster killall -9 corosync would do it! What should now happen? Well, the cluster has no idea what that node is doing with the resources it was running - are they still running?
Might they start running in the future? Once this is enabled the default your cluster will refuse to run unless at least one stonith resource is in place.Configuring Stonith Fence Device In Suse Linux Enterprise Server 12- SuSe HAE Cluster-Part-3
To see the documentation for each plugin, run the following inserting the name from the above list :. Most plugins will offer to reset or poweroff the node. If your route of communication to the node is down for pacemaker, you might also have no route to stonith - this is especially true for devices such as IPMI which share a network connection and power source with the node. You can setup more than one stonith device, and configure their use order using the priority parameter.
All of the above is fine with 3 or more nodes in your cluster, but what can you do if you run a 2-node cluster? The obvious advice is to turn it into a 3-node cluster for quorum. The second option can be achieved by removing the service section from your corosync. This is another variation for 2-node clusters, which also requires a 3rd machine, though not one managed in this pacemaker cluster. Loss of access to the disks, or noticing a fencing request being written to the disk will cause that node to fence itself.
The following are all worth a read to add more information to your understanding of these issues:.Fencing is a very important concept in computer clusters for HA High Availability. Unfortunately, given that fencing does not offer a visible service to users, it is often neglected. Fencing may be defined as a method to bring an HA cluster to a known state.
But, what is a "cluster state" after all? To answer that question we have to see what is in the cluster. Any computer cluster may be loosely defined as a collection of cooperating computers or nodes. Nodes talk to each other over communication channels, which are typically standard network connections, such as Ethernet.
The main purpose of an HA cluster is to manage user services. To the cluster, however, they are just things which may be started or stopped. This distinction is important, because the nature of the service is irrelevant to the cluster.
In the cluster lingo, the user services are known as resources. Every resource has a state attached, for instance: "resource r1 is started on node1". In an HA cluster, such state implies that "resource r1 is stopped on all nodes but node1", because an HA cluster must make sure that every resource may be started on at most one node.
Every node must report every change that happens to resources. This may happen only for the running resources, because a node should not start resources unless told so by somebody. So far so good. But what if, for whatever reason, we cannot establish with certainty a state of some node or resource?
This is where fencing comes in. If you wonder how this can happen, there may be many risks involved with computing: reckless people, power outages, natural disasters, rodents, thieves, software bugs, just to name a few. We are sure that at least a few times your computer failed unpredictably.
Chapter 4. Fencing: Configuring STONITH
Using the resource level fencing the cluster can make sure that a node cannot access one or more resources. The resource level fencing may be achieved using normal resources on which the resource we want to protect would depend.
Such a resource would simply refuse to start on this node and therefore resources which depend on it will be unrunnable on the same node as well. The node level fencing makes sure that a node does not run any resources at all. This is usually done in a very simple, yet brutal way: the node is simply reset using a power switch. This may ultimately be necessary because the node may not be responsive at all. Before we get into the configuration details, you need to pick a fencing device for the node level fencing.
There are quite a few to choose from. If you want to see the list of stonith devices which are supported just run:.STONITH is traditionally implemented by hardware solutions that allow a cluster to talk to a physical server without involving the operating system OS. Although hardware-based STONITH works well, this approach requires specific hardware to be installed in each server, which can make the nodes more expensive and result in hardware vendor lock-in.
A disk-based solution, such as split brain detection SBDcan be easier to implement because this approach requires no specific hardware. If something goes wrong with a node in the cluster, the injured node will terminate itself. Please check the box if you want to proceed. VMware's vRealize suite and its acquisitions of CloudHealth and other startups bolstered its cloud management reputation. Use VMware Host Profiles to keep configuration consistent between hosts and clusters across your vSphere, and avoid common errors VMware vMotion is a function of vSphere that enables live migrations of VMs to ease load balancing and maintenance.
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Server hardware has consistently evolved since the s. CPUs have evolved to meet ever-increasing technology demands. We look at the way performance and power characteristics have The quantum computing industry is entering a new era.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.
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Stonith and Quorum in Pacemaker
Skip to content. Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Sign up. Converting log file of Pacemaker with Corosync stack for system operator. Python M4 Makefile Shell. Python Branch: master.
Find file. Sign in Sign up. Go back. Launching Xcode If nothing happens, download Xcode and try again. Latest commit Fetching latest commit…. Apr 24 pm01 info: Resource prmIp stopped. Apr 24 pm01 info: Resource prmFs stopped.
Apr 24 pm01 info: Resource prmEx stopped. Apr 24 pm02 info: Resource prmFs started. Apr 24 pm02 info: Resource prmIp started. Apr 24 pm02 info: Resource prmPg started. Apr 24 pm01 error: Resource prmPg failed to stop. Apr 24 pm02 info: Resource prmEx started. You signed in with another tab or window. Reload to refresh your session. You signed out in another tab or window.Fencing is a very important concept in computer clusters for HA High Availability.
A cluster sometimes detects that one of the nodes is behaving strangely and needs to remove it. Fencing may be defined as a method to bring an HA cluster to a known state. Every resource in a cluster has a state attached. Every node must report every change that happens to a resource. The cluster state is thus a collection of resource states and node states. When the state of a node or resource cannot be established with certainty, fencing comes in.
Even when the cluster is not aware of what is happening on a given node, fencing can ensure that the node does not run any important resources. There are two classes of fencing: resource level and node level fencing.
The latter is the primary subject of this chapter. Resource level fencing ensures exclusive access to a given resource. Common examples of this are changing the zoning of the node from a SAN fiber channel switch thus locking the node out of access to its disks or methods like SCSI reserve.
Node level fencing prevents a failed node from accessing shared resources entirely. This is usually done in a simple and abrupt way: reset or power off the node. The High Availability Extension includes the stonith command line tool, an extensible interface for remotely powering down a node in the cluster. For an overview of the available options, run stonith --help or refer to the man page of stonith for more information. To use node level fencing, you first need to have a fencing device.
Power Distribution Units are an essential element in managing power capacity and functionality for critical network, server and data center equipment. They can provide remote load monitoring of connected equipment and individual outlet power control for remote power recycling. A stable power supply provides emergency power to connected equipment by supplying power from a separate source if a utility power failure occurs.
If you are running a cluster on a set of blades, then the power control device in the blade enclosure is the only candidate for fencing. Of course, this device must be capable of managing single blade computers.
However, they are inferior to UPS devices, because they share a power supply with their host a cluster node. If a node stays without power, the device supposed to control it would be useless. Testing devices are used exclusively for testing purposes. They are usually more gentle on the hardware.
Before the cluster goes into production, they must be replaced with real fencing devices. It accepts the commands which correspond to fencing operations: reset, power-off, and power-on. It can also check the status of the fencing device. The pacemaker-fenced daemon runs on every node in the High Availability cluster.
The pacemaker-fenced instance running on the DC node receives a fencing request from the pacemaker-controld. It is up to this and other pacemaker-fenced programs to carry out the desired fencing operation. All STONITH plug-ins look the same to pacemaker-fencedbut are quite different on the other side, reflecting the nature of the fencing device. Some plug-ins support more than one device. All configuration is stored in the CIB. Starting and stopping are thus only administrative operations and do not translate to any operation on the fencing device itself.
However, monitoring does translate to logging it to the device to verify that the device will work in case it is needed.