# Patent

## Title
Reliable fault resolution in a cluster

## Abstract

A method and system for localizing and resolving a fault in a cluster environment. The cluster is configured with at least one multi-homed node, and at least one gateway for each network interface. Heartbeat messages are sent between peer nodes and the gateway in predefined periodic intervals. In the event of loss of a heartbeat message by any node or gateway, an ICMP echo is issued to each node and gateway in the cluster for each network interface. If neither a node loss not a network loss is validated in response to the ICMP echo, an application level ping is issued to determine if the fault associated with the absence of the heartbeat message is a transient error condition or an application software fault.

## Background
CROSS REFERENCE TO RELATED APPLICATION(S)
The present application is a continuation of U.S. patent application Ser. No. 10/649,269, filed Aug. 27, 2003 now U.S. Pat. No. 7,284,147, and is hereby incorporated by reference.


BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to a method and system for resolving a fault in a cluster of multi-homed nodes in a computer, storage or communication system. More specifically, the invention relates to detecting and isolating the fault to determine origination of the fault to enable appropriate failover and repair action.
2. Description of the Prior Art
A node is a computer running single or multiple operating system instances. Each node in a computing environment has a network interface that enables the node to communicate in a local area network. A cluster is a set of one or more nodes coordinating access to a set of shared storage subsystems typically through a storage area network. It is common for a group of nodes to be in communication with a gateway for connection of a local area network to another local area network, a wider intranet, or a global area network. Each network interface and each gateway in a local area network includes an identifying IP address.
It is also known in the art for nodes in a local or wide area network to include two network interfaces, also known as “multi-homed nodes”. The two network interface configuration provides redundant connectivity. Multi-homed nodes possess software that has access to both network interfaces. In the event of a failure associated with one of the network interfaces or the path along the network interface, the communication may switch to the second network interface on the same node, i.e. failover, without interruption or loss of data or of service from the node.
One form of resolving faults in a network is to require a peer node to issue or request a response protocol message on a suspect network interface. This solution attempts to solve the specific problem of validating the network path loss, as well as determining whether the fault is associated with a local or remote interface network. However, this technique relies on a potentially unreliable server on a remote node to issue a ping to the local network interface. This technique only functions under a single fault scenario. Any network fault or software fault affecting the remote node will provide a false conclusion on the local node.
Other solutions include redundant heartbeats and heartbeat channels between nodes, and link failures to resolve network faults. The use of redundant heartbeats and heartbeat channels solves the problem associated with reliable detection of a node loss, but fails in the area of network loss resolution. Similarly, link failures for resolving network faults are limited to provide network failover support, but do not function with an integrated high availability architecture with node and network monitoring and integrated node and network path failover support. In addition, the link failures technique does not have the ability to determine if a network partition has occurred for which the failover requires cluster reformation. Finally, such solutions which are typically provided by network drivers function only in a single subnet network topology.
The prior art methods for reliably detecting and resolving a fault are either in an efficient or unreliable in an integrated high availability architecture or cannot work reliably in a two node cluster. Accordingly, a method and system for reliable and efficient detection and resolution of a fault in an integrated high availability architecture is desired.
SUMMARY OF THE INVENTION
This invention comprises a method and system for resolving faults in a computer system.
In one aspect of the invention, a method is provided for fault resolution in a computer system. A cluster is configured with a gateway for a network interface. It is determined whether there is a heartbeat loss in the cluster. If there is a heartbeat loss in the cluster, the loss is validated and localized. The localization of the loss is conducted by analyzing a response echo.
In another aspect of the invention, an article is provided with a computer-readable medium having computer-readable instructions stored thereon that are executable by a processor. Instructions are provided in the medium to determine a heartbeat loss in a cluster configured with a gateway for a network interface. In addition, instructions are provided in the medium to validate the heartbeat loss. In response to the validation, instructions are provided in the medium to localize the loss through analysis of a response echo.
In yet another aspect of the invention, a computer system is provided with a cluster of multi-homed nodes. A gateway is provided in the computer system. The gateway is in communication with the cluster and configured for a network interface. In response to detection of a heartbeat loss, an operating system ICMP echo is configured to be issued to peer nodes in the cluster and to the gateway through the network interface. A response from the echo is analyzed for location of a fault in the cluster.
Other features and advantages of this invention will become apparent from the following detailed description of the presently preferred embodiment of the invention taken in conjunction with the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a prior art multi-node computing system.
FIG. 2 is a block diagram of a multi-node computing system according to the preferred embodiment of this invention, and is suggested for printing on the first page of the issued patent.
FIGS. 3A and 3B are a flow diagram illustrating the process of locating and resolving a fault in the computer system.



DESCRIPTION OF THE PREFERRED EMBODIMENT
Overview
A cluster is configured with multi-homed nodes and at least one gateway for each network interface. Heartbeat messages are sent between peer nodes in the cluster in predefined periodic intervals. In response to loss of a heartbeat message, an ICMP echo is sent to all nodes and gateways in the cluster through both network interfaces. Sending the ICMP echo to all nodes in the cluster and the gateway assists in resolving whether or not a fault has occurred, a network partition has occurred, as well as determine the location of a node loss, a fault associated with a network interface, and/or a cable fault. An application level ping may be issued to further localize the fault. Accordingly, the use of the ICMP echo for each node and gateway in the cluster through each network interface reliably localizes a fault and provides for an efficient resolution of the fault condition.
Technical Details
It is known in the art to send heartbeat messages to peer nodes in a network at predefined intervals. FIG. 1 is a block diagram 10 of a prior art multi-node computing system. In this illustration, the arrow represent heartbeats and the straight lines represent network paths. There are three nodes in the system, Node0 (20), Node1 (30), and Node2 (40). Each node is a multi-homed node. As shown in FIG. 1, Node0 (20) has network interface1 (22) and network interface2 (24). Similarly, Node1 (30) has network interface1 (32) and network interface2 (34), and Node2 (40) has network interface1 (42) and network interface2 (44). As shown in FIG. 1, heartbeat messages are sent to adjacent peer nodes in a network. For example, Node0 (20) sends first heartbeat messages (50) and (52) to Node1 (30) and Node2 (40), respectively, across the first network interface (22), (32), and (42), and sends second heartbeat messages (54) and (56) to Node1 (30) and Node2 (40), respectively, across the second network interface (24), (34), and (44). Similarly, Node1 (30) sends first heartbeat messages (50) and (58) to Node0 (20) and Node2 (40), respectively, across the first network interfaces (22), (32), and (42), and sends second heartbeat messages (54) and (60) to Node0 (20) and Node2 (40) across the second network interfaces (24), (34), and (44), and Node2 (40) sends first heartbeat messages (52) and (58) to Node0 (20) and Node1 (30) across the first network interface (22), (32), and (42) and sends second heartbeat messages (56) and (60) to Node0 (20) and Node1 (30) across the second network interface (24), (34), and (44). Essentially, each node sends independent periodic heartbeat messages to adjacent peer nodes across each network interface. The heartbeat message is bi-directional and exists between adjacent nodes to monitor faults within a node. However, the heartbeat messages are not capable of resolving a network loss. Accordingly, the heartbeat message is useful for determining faults on a nodal level only without resolving such faults, if any.
FIG. 2 is a block diagram (100) of one example of a multi-homed multiple node computing system with one Gateway (180) for two network interfaces. In this illustration, there are three nodes in the system, Node0 (110), Node1 (120), and Node2 (130). Each node is a multi-homed node. As shown in FIG. 2, Node0 (110) has network interface1 (112) and network interface2 (114). Similarly, Node1 (120) has network interface1 (122) and network interface2 (124), and Node2 (130) has network interface1 (132) and network interface2 (134). In addition to the multiple network interfaces, the system has a Gateway (180) for communication with network interface1 (112), (122), and (132) and with network interface2 (114), (124), and (134). As shown in FIG. 2, heartbeat messages are sent to adjacent peer nodes in a network. For example, Node0 (110) sends first heartbeat messages (152) and (158) to Node1 (120) and Node2 (130) across the first network interface (112), (122), and (132) and sends second heartbeat messages (150) and (160) to Node1 (120) and Node2 (130) across the second network interface (114), (124), and (134). Similarly, Node1 (120) sends first heartbeat messages (152) and (156) to Node0 (110) and Node2 (130), respectively, across the first network interfaces (112), (122), and (132), and sends second heartbeat messages (150) and (154) to Node0 (110) and Node2 (130) across the second network interfaces (114), (124), and (134), and Node2 (130) sends first heartbeat messages (156) and (158) to Node1 (120) and Node0 (110) across the first network interface (112), (122) and (132), and sends second heartbeat messages (154) and (160) to Node1 (120) and Node0 110 across the second network interface (114), (124) and (134). In addition, the Gateway (180) is present along the network paths for both network interfaces. The Gateway (180) does not receive or send heartbeat messages since heartbeat messages are an application level protocol, and the Gateway (180) is limited to operating system level protocols. The presence of the Gateway (180) enables detection of a fault on an operating system level, such as a fault associated with a network path or any component in the path, such as a card, switch or hub. Accordingly, each node sends periodic bi-directional heartbeat messages to adjacent peer nodes across each network interface to monitor faults within the associated network with a gateway present in the network topology.
Bi-directional heartbeat messages are used to monitor loss of communication with a node. In the event of loss of a heartbeat message by a peer node, an ICMP message is used for out-of-band messages related to network operation or failure thereof. An ICMP echo function sends an internet protocol packet on a round trip between hosts. Similarly, a ping which uses an application level protocol in place of an operating system protocol is used to send a message intended to be echoed back by the recipient. An application level ping places a unique sequence number on each packet it transmits, and reports which sequence numbers it receives back. This enables a system operator to determine if packets have been dropped, duplicated, or reordered. In addition, the ping function places a timestamp in each packet, which is echoed back and can be used to compute how long each packet exchange took, i.e. the round trip time. In addition, the ping reports other ICMP messages, such as if a router is declaring the target host unreachable.
FIGS. 3A and 3B are a flow diagram (200) illustrating the process of location and resolving a fault in the multi-homed multiple node computing system (100) as shown in FIG. 2 using heartbeat messages, ICMP echoes, and optionally an application level ping. Heartbeat messages are sent to peer nodes for monitoring fault detection (202). A test (204) is conducted to determine if there is a loss of a heartbeat on either network interface. A negative response to the query at step (204) is followed by a return to step (202) to continue the process of sending heartbeat messages at predefined intervals. However, a positive response to the query at step (204) is indicative of a loss of a heartbeat by a specific node. ICMP echoes are subsequently issued by the node detecting the heartbeat loss (206). The ICMP echo is sent from the node detecting the heartbeat loss to all peer nodes and gateways in the cluster on both network interfaces. One set of ICMP echoes is sent on the first network interface, and a second set of ICMP echoes is sent on the second network interface. The number of echoes issued in response to loss of a heartbeat is the following:

Number of Echoes=[(N−1)+(Quantity of Gateways)]*(Number of Network Interfaces)

where N is representative of the number of nodes in the system. The ICMP echo is issued to the operating system on each node. Accordingly, issuance of the echo requests a response message from the operating system running on one or more nodes in the cluster of which one or more of the nodes may have a fault.

The ICMP echo responses function to validate suspicion of a node loss or a network path loss. Following issuance of the ICMP echo, a test is conducted to determine if at least one echo return has been received for a network interface (208). A positive response to the test at step (208) is indicative that the network path along that network interface is functioning (210). Thereafter, a comparison of echo responses from the target node set for the network interfaces is conducted to determine the best path of connectivity along either network interface within the cluster (212). A test is subsequently conducted to determine if there is improved connectivity on the alternate network path (214). A negative response to the test at step (214) is followed by a return to step (202). However, a positive response to the query at step (214) results in a network path failover (216). Accordingly, if at least one echo return is produced a network connectivity problem is localized and resolved.
However, if a response to the test at step (208) is negative, this is indicative that the fault does not reside in the network path. Therefore, a test is conducted to determine if redundant echoes from the same peer node have been returned (218). A negative response to the test at step (218) is validation of a peer node fault pertaining to node hardware and/or operating system fault of the peer node (220). Thereafter, a node failover or cluster reformation is conducted (222). In the event neither a node loss nor a network loss is validated by the ICMP echo response, an application level ping is issued (224). Following the issuance of the ping, a test is conducted to determine if there is a response to the ping (226). A ping response is suggestive of a transient error condition (228), whereas absence of a ping response within a predefined time interval is suggestive of an application software fault (230). If the fault is not in the network connectivity, subsequent tests are conducted to determine and locate alternative faults that may reside with a node fault, a transient error condition, or an application software fault. Accordingly, localizing the fault helps determine the best course of action for automatic recovery and/or administrative repair action.
Advantages Over the Prior Art
A gateway with a routing table for both network interfaces and associated messages is configured within the physical computer system and application software. The routing table enables efficient transmission of messages and echoes across each of the networks. In addition, the configuration of the computer system with a gateway for each network interface enables control issuance of an ICMP echo to a specific network. Finally, the placement of the gateway within the network configuration assists in determining whether a suspected fault resides in the network or a node within the network. In particular, it helps resolve faults in two node clusters and network partitions in general. Accordingly, placement of the gateway within the computer system provides enhanced efficiency and reliability in locating and resolving a fault in the system.
Alternative Embodiments
It will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. In particular, the invention should not be limited to the architectural layout of the system shown in FIG. 2. Each network may include multiple gateways and alternate designs for connecting the nodes and gateways. In addition, the network topology could be a single subnet, a dual subnet, or redundant physical networks. Accordingly, the scope of protection of this invention is limited only by the following claims and their equivalents.

## Claims

1. A method for resolving a fault in a computer system comprising:
determining a heartbeat loss in a cluster configured with a gateway for a network interface;
validating said heartbeat loss, including sending an ICMP echo to all peer nodes in said cluster and said gateway through said network interface; and
localizing said heartbeat loss including differentiating between a node fault and a network fault by analyzing a response echo.

2. The method of claim 1, further comprising determining a best path of connectivity through a comparison of echo response.

3. An article comprising:
a computer-readable medium having computer-readable instructions stored thereon executable by a processor, said computer-readable instructions comprising:
instructions to determine a heartbeat loss in a cluster configured with a gateway for a network interface;
instructions to validate said heartbeat loss, including sending an ICMP echo to all peer nodes in said cluster and said gateway through said network interface; and
instructions to localize said loss including differentiating between a node fault and a network fault through analysis of a response echo.

4. The article of claim 3, further comprising instructions to determine a best path of connectivity to a specific peer node through a comparison of said echo responses going through different network interfaces associated with the specific peer node.

5. A computer system, comprising:
a cluster of nodes, each node having at least two network interfaces;
a gateway in communication with said cluster and configured for a network interface;
an operating system ICMP echo adapted to be issued to all peer nodes in said cluster and to said gateway through said network interface in response to a heartbeat loss detection; and
a response from said echo adapted to be analyzed for location of a fault in said cluster including differentiating between a node fault and a network fault and determination of an intended recipient of said echo.

6. The system of claim 5, wherein receipt of a return of said echo from said peer nodes for said network interface within a predefined time interval is indicative of operation of said network interface.

7. The system of claim 6, wherein absence of receipt of a return of said echo from peer nodes for said network interface within a predefined time interval is indicative of a fault selected from a group consisting of: a peer node fault, a network fault local to the peer node, and combinations thereof.

8. The system of claim 5, wherein receipt of a return of said echo from said gateway for said network interface within a predefined time interval is indicative of operation of said network interface.

9. The system of claim 5, further comprising an application level ping adapted to be issued to a peer node in response to both receipt of said echo within a predefined time interval and a heartbeat beat loss detection.

10. The system of claim 5, further comprising a comparison tool adapted to compare an echo response from a target node for each network interface.

11. The system of claim 10, wherein said comparison tool determines a network interface path based upon criteria selected from the group consisting of: maximum availability of nodes in said network, availability of said gateway in said network, and combinations thereof.