6. Network partition resolution resources details¶
This chapter provides detailed information on network partition resolution resources.
This chapter covers:
6.2. Understanding the network partition resolution resources
6.3. Understanding network partition resolution by PING method
6.4. Understanding network partition resolution by HTTP method
6.1. Network partitions¶
6.2. Understanding the network partition resolution resources¶
Servers in a cluster monitor other servers by using heartbeat resources. When all heartbeat resources are disconnected or other server is shut down by a server not in a cluster, the network partition is solved using network partition resolution resources. The following network partition resolution resource is provided.
Network partition
resolution resources
|
Abbreviation |
Function Overview |
---|---|---|
PING network partition resolution resource (PING method) |
pingnp |
A network partition is solved by determining a server that can communicate using the ping command. |
HTTP network partition resolution resource (HTTP method) |
httpnp |
A network partition is solved by determining a server that can communicate, sending HTTP HEAD request to Web server. |
If there is only one available LAN on the configuration, set the PING network partition resolution resource or the HTTP network partition resolution resource.
6.2.1. Network partition resolution during cluster service start¶
When cluster services are started but all heartbeat routes to other servers are found cut off, resolving the network partitions takes place. In this case, the cluster services are stopped on the servers with the detected network partitions. Check the statuses of the heartbeat routes, then manually start the cluster services.
6.3. Understanding network partition resolution by PING method¶
6.3.1. Settings of the PING network partition resolution resources¶
To use PING network partition resolution resources, a device that is always active to receive and respond to the ping command (hereafter described as ping device) is required.
When the heartbeat from another server is lost but the ping device is responding to the ping command, the remote server is down. Failover starts.
If there is no response to the ping command, it is determined that the local server is isolated from the network due to network partitioning an action when a network partition occurs is performed.
![Two servers and a ping device](_images/img_settings-of-the-ping-network-partition-resolution-resources-10.png)
Fig. 6.1 PING network partition resolution resources (1)¶
When the heartbeat from the other server is found lost and the ping device does not respond to the ping command, the server is shut down. This prevents a split brain syndrome in the same group of both the active and standby servers.
![Two servers and a ping device](_images/img_settings-of-the-ping-network-partition-resolution-resources-20.png)
Fig. 6.2 PING network partition resolution resources (2)¶
For details, see "Fencing tab" in "Cluster properties"in "Parameter details" in this guide.
6.3.2. Note on PING network partition resolution resource¶
When using PING network partition resolution resource, specify addresses which can be sent from and received to through one of the interconnect LANs registered in the configuration information.
In case that response to ping command continues not returning on all the all servers before disconnection of the heartbeat due to ping device failure or other reasons, network partition cannot be resolved. If the heartbeat disconnection is detected in this situation, an action when a network partition occurs is performed on all servers.
![](_images/clp_image381.png)
6.4. Understanding network partition resolution by HTTP method¶
6.4.1. Settings of the HTTP network partition resolution resources¶
To use the HTTP network partition resolution resources, the following settings are required.
An all time running server with HTTP communication available (hereafter referred to as Web server) is needed.
When the heartbeat from another server is detected to be stopped, the HTTP network partition resolution resource operates in the following two ways: If there is a response from Web server, it determines it as a failure of another server and executes the failover. If there is no response from Web server, it determines that the network partition status isolated the local server from the network and executes the same operation as when the network partition occurs.
![Two servers, and a Web server always running](_images/img_settings-of-the-http-network-partition-resolution-resources-10.png)
Fig. 6.3 HTTP network partition resolution resources (1)¶
When the heartbeat from the other server is found lost and there is no response from the Web server, the server is shut down. This prevents a split brain syndrome in the same group of both the active and standby servers.
![Two servers, and a Web server always running](_images/img_settings-of-the-http-network-partition-resolution-resources-20.png)
Fig. 6.4 HTTP network partition resolution resources (2)¶
For more information, refer to "Fencing tab" in "Cluster properties" in "Parameter details" in this guide.
6.4.2. Note on HTTP network partition resolution resource¶
When using HTTP network partition resolution resource, specify addresses which can be sent from and received to through one of the interconnect LANs registered in the configuration information.
- Specify a device which responds to HTTP HEAD requests.Responding to a HEAD request with a status code 200 or 301, the target is considered normal.Responding with a status code other than 200 and 301 or not responding, the target is considered abnormal.
In the communication with Web server, NIC and a source address are selected according to the OS settings.
6.5. Not resolving network partition¶
When this method is selected, network partition resolution is not performed. Therefore, if a failure occurs on all the network channels between servers in a cluster, all servers fail over.