Cluster

A TIPC cluster consists of nodes interconnected with links. A node can be either a physical processor, a virtual machine or a network namespace, e.g., in the form of a Docker container. A link constitutes a reliable packet transport service, sometimes referred to as an "L2.5" data link layer.

• It guarantees delivery and sequentiality for all packets.
• It acts as a trunk for inter-node connections, and keeps track of those.
• When all contact to the peer node is lost all sockets with connections to that peer are notified so they can break the connections.
• Each endpoint keeps track of the peer node’s address bindings in the local replica of the binding table.
• When contact to the peer node is lost all bindings from that peer are purged and service tracking events issued to all matching subscribers.

• When there is no regular data packet traffic each link is actively supervised by probing/heartbeats.
• Failure detection tolerance is configurable from 50 ms to 30 seconds, - default setting is 1.5 seconds.
• For performance and redundancy reasons it is possible to establish two links per node pair, - on separate network interfaces.
• A link pair can be configured for load sharing or active-standby.
• If a link fails there will be a disturbance-free failover to the remaining link, if any.

A cluster has a 32 bit cluster identity, which determines the cluster setup.

• The cluster identity can be assigned by the user if anything different from the default value is needed, e.g., if there is more than one cluster on the same subnet.
• All nodes using the same cluster identity will establish mutual links.
• Neighbor discovery is performed by UDP multicast or L2 broadcast, when available.
• If broadcast/multicast support is missing in the infrastructure, discovery can be performed by explicitly configured IP addresses

Each node has a cluster unique node identity.

• In versions before Linux 4.17 this is a 32 bit structured address which must be set by the user.
• In later versions is it a 128 bit field with no internal structure or restrictions.
• This identity is by default set by the system, based on a MAC or IP address.
• It can also be set by the user, e.g., based on a host name or a UUID.
• The identity is internally hashed into a guaranteed unique 32 bit node address, which becomes the node address used by the protocol.
• The two identity formats are compatible, and can be used in the same cluster.

Since Linux 4.7, TIPC comes with a unique, patent pending, auto-adaptive hierarchical neighbor monitoring algorithm. This makes it possible to establish full-mesh clusters of up to 1000 nodes with a failure discovery time of 1.5 seconds, which it in smaller clusters can be made much shorter.