Category: Ipmi fencing

When a server or a software application develops a fault in a high-availability software framework, it is essential to isolate the affected component and remove it from operation in order to protect the integrity of the cluster as a whole, and to protect data hosted by the cluster from corruption. In shared-storage HA clusters, such as those running Lustre storage services, data corruption is most likely to occur when multiple services on different nodes try to access the same data storage concurrently.

Each service assumes that it has exclusive access to the data, which leads to a risk that one service might overwrite information committed by another service on a different cluster node. There are some protections in place in Ldiskfs and to a lesser extent ZFS that minimize the risk of concurrent access, but HA software frameworks such as Pacemaker provide additional protections to further reduce exposure to this risk. The mechanism for isolating a failed component is called fencing.

Fencing is the means by which a node in a cluster is prevented from accessing the shared storage. This is usually achieved by forcing the failed node to power off. In Pacemaker, once a fault is detected, healthy nodes that are able to form a quorum create a new cluster configuration with the faulty node removed.

The faulty node is then fenced, and any services that were running on the now isolated server are migrated to the surviving node or nodes.

STONITH relies on healthy cluster nodes detecting a fault or failure in another node, and forcibly removing that faulted node from the cluster using a brute force mechanism such as power cycling the host. Pacemaker has a set of software components called fencing agents that are used for this purpose. There are several such agents available, but most conform to the same basic principal of fault isolation through power control.

All such agents rely on supporting infrastructure to facilitate power control, and each has its own specific requirements and parameters. These are vendor-specific interfaces, and provide a high level of reliability in the mechanism, because they require only that there is access to the PDU control interface.

There are several RPMs available that contain fencing agents. It is simplest to just install the superset meta RPM package, called fence-agents-all Note: the YUM package name fence-agents is an alias for fence-agents-all. To obtain a full list of the available agents installed on a host with the PCS software installed:. Fencing is notoriously difficult to configure correctly, as it is difficult to anticipate and test all of the potential failure modes.

If the fencing agent does not exit cleanly and without reporting an error, then the fencing operation will be regarded by Pacemaker as failed, and the resources hosted by the failed node will not be migrated to a healthy cluster node. This is because the agent did not report success when isolating the affected node. Rather than risk compromising the integrity of any data associated with the resources by potentially running multiple services on both the healthy and unhealthy cluster nodes, Pacemaker will refuse to migrate resources until it can be sure that the faulty node has been isolated.

Fencing is a complex topic and there are a number of parameters that can be set to control the behavior of fencing in a Pacemaker cluster. This guide is not a comprehensive reference on the topic, but provides an introduction to the basic mechanisms, illustrated by some examples. The command must be run for each node in the cluster each cluster node must have its own fence agent resource but the commands can be run from a single node.

This means that a user with suitable privileges on a cluster node will be able to retrieve the password of the IPMI user. The list of nodes is managed through the following options:.Please adapt the example below to the names, addresses, credentials and fence agents you are using in your cluster.

In order for fencing to work when two separate PDUs are used, we must ensure that there is a period of time where both PDUs have their ports powered off at the same time. To do this, we need to setup four primitives; One for each device set to an "off" action and another for each device set to an "on" action.

Now configure the four PDU fence methods for "pcmk-1". Later, we will stitch these actions together and this argument will tell pacemaker to wait 5 seconds after turning off the second PDU before restoring power. This gives plenty of time for the node's power supplies to completely drain, ensuring that the node loses power. You will also note that the "monitor" operation is only set on the "off" actions.

There is no need to monitor the status of the "on" actions as it would be redundant. The next step is to tell pacemaker what order we want the fencing methods to run, using fencing levels. Each fencing level may have one or more fence devices.

When fencing is required, Pacemaker will try each level in sequence, stopping at the first level that succeeds. Therefore, separate levels function as a "fallback" mechanism logical "or".

At any given level, all the devices in that level will be tried in succession, and all must succeed for the level to succeed logical "and". You can and should! If you configured your server's BIOS to power on after power loss or to return to last state after power loss, your server should start to power back on.

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ipmi fencing

Category : Fencing. Note : Prior to version 1. If you have a version of pacemaker below this including 1.Forums New posts Search forums. What's new New posts Latest activity.

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Configure Multiple Fencing Devices Using pcs

New posts. Search forums. Install the app. Thread starter rafman Start date Feb 16, Tags fencing ha proxmox 4 high avaibility.

Chapter 4. Configuring IPMI Management Boards as Fencing Devices

JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding. You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser. Feb 14, 8 2 1 Switzerland. Hi, We are testing a Proxmox Cluster. But not on HP Servers.

That helped a lot! During testing it sometimes happend that machines rebooted randomly when others were rebooted as well. I guess, the nofailback option is the solution to the maintenance problem. Thanks again.

The random rebooting just happened once. It would be however still nice to have to option to disarm fencing, just in case something goes wrong. Is that not possible currently? Why would you disarm fencing? You are supposed to migrate VMs before rebooting a node. For HW watchdogs, be aware that a server has several ones nowadays.Iron Maiden — Wasted Years. RedHat Cluster Suite uses fencing as a safety measure for split brain scenario.

Split brain is a situation when a cluster creates two or more partitions. Each partition thinks it is the only active and tries to start services. Now, the most benign situation that can occur in this scenario is IP conflict. Another, much worse situation is if two nodes try to write to same shared filesystem. To circumvent these situation, some kind of eviction of nodes has to occur.

RedHat Cluster Suite leans on fencing mechanism. Fencing usually does some of the following:. First, IPMI has to be enabled. At the bottom of that page, you can find settings section for IPMI.

Now all you have to do is to create a user with IPMI privileges. In the user configuration window, I recommend following settings:. You can also test hard reboot, if you wish:. Congratulations, your server has just been rebooted! You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account.

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ipmi fencing

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Top Blog at WordPress. Post to Cancel. By continuing to use this website, you agree to their use.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.

ipmi fencing

There are two classes of fencing: resource level and node level fencing. The latter is the primary subject of this chapter. Using resource level fencing the cluster can ensure that a node cannot access one or more resources. Resource level fencing can be achieved by using normal resources on which the resource you want to protect depends.

Such a resource would simply refuse to start on this node and therefore resources which depend on it will not run on the same node. Node level fencing ensures that a node does not run any resources. This is usually done in a simple if brutal way: reset or power off the node. It provides node level fencing. 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.

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Configure Hardware Watchdog / IPMI Fencing

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