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Fencing mechanism

The fencing mechanism is used to halt nodes that are in inconsistent state. The fencing is required to have a correctly working cluster. Without it, the cluster cannot stop inconsistent nodes making the whole concept of High Availability impossible.

The project provides the next fencing options:

  • SBD
  • Cloud native fencing (see ../<provider>/README.md for details).

Usually the cloud native fence mechanism is recommended as it simpler and less expensive.

SBD

SBD (Storage Based Death) uses a shared disk among the nodes to halt the nodes.

Find more information in:

The next options are available to use SBD as the cluster fencing mechanism.

ISCSI server

Use a shared disk served by an ISCSI server. This is a quite standard option if the clusters are hosted in the cloud, as shared disks are not commonly available. To use this option, an ISCSI server must be created (or use an already existing one). The project gives the option to create a new virtual machine to host this service. For that we need to use the next variables:

  • Set sbd_storage_type to iscsi
  • Enable at least one cluster that will use SBD setting the option *_cluster_fencing_mechanism to sbd
  • ISCSI server configuration has some advanced configuration options. Check the terraform template examples and the available variables for that.

Shared disk

Use a shared disk attached to all clustered nodes. This option is only available for libvirt. To use this option:

  • Set sbd_storage_type to shared-disk
  • Enable at least one cluster that will use SBD setting the option *_cluster_fencing_mechanism to sbd

Cloud native fencing

The cloud native fencing mechanism is based in capabilities of the cloud providers to halt the virtual machines using their own APIs. This means that there is not any need to have additional machines or resources, making them simpler and less expensive. This option is only available for AWS and GCP by now.

To use this option:

  • Set *_cluster_fencing_mechanism to native to the clusters that have to use this mechanism.