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We Have Summarized Methods of Switching the Connection Destination of EXPRESSCLUSTER X on On-premises

EXPRESSCLUSTER Official Blog

June 13th, 2024

Machine translation is used partially for this article. See the Japanese version for the original article.

Introduction

EXPRESSCLUSTER is software for achieving high availability, and it makes the business application redundant and automatically switches the server on which the business application is operating in the event of a failure. At this time, the client will not automatically switch the server to which it connects, so a method is needed so that the client does not have to be aware that the server on which the business application is operating has been switched. EXPRESSCLUSTER provides a method for clients to access the business application without being aware of the server switch by the switching the connection destination function.

In this article, we will introduce the function and selection methods of switching the connection destination for HA cluster configuration on on-premise environments.

Contents

1. Methods of Switching the Connection Destination on On-premises Environment

1.1 List of Switching the Connection Destination Methods

EXPRESSCLUSTER provides a method to switching the connection destination when the server on which the business application is operating is switched due to a failure, etc. so that the client can access the business application without being aware of the server change. Specifically, EXPRESSCLUSTER assigns virtual IP address or virtual host name to the server on which the business application is operating, and the client can access the business application without being aware of the server switch by accessing via these virtual IP address or virtual host name.

The connection destination switching function(group resources) and switching targets of EXPRESSCLUSTER on on-premises environment are as follows.

Group resources name Switching target
Floating IP resource Floating IP address
Virtual IP resource Virtual IP address
Virtual computer name resource Virtual computer name
Dynamic DNS resource Virtual host name

1.2 How to Select Switching the Connection Destination Methods

Which of the connection destination switching function(group resources) provided by EXPRESSCLUSTER are available for HA clusters on on-premise environments depends on how clients access the HA cluster and how the servers that constitute the HA cluster are placed.

How clients access the HA cluster:

  • Access the HA cluster from a client by IP address
  • Access the HA cluster from a client by hostname

How the servers that constitute the HA cluster are placed:

  • Place cluster servers in the same segment
  • Place cluster servers between different segments
The functions(group resources) that can be used depending on the combination of the business application access method and cluster servers installation location are summarized below.

  IP address Hostname
In the same segment Floating IP resource Virtual computer name resource
Dynamic DNS resource
Between different segments Virtual IP resource Dynamic DNS resource

There are two methods for configuring access to the business application using IP address. The basic idea is that a floating IP address is the IP address used when constructing an HA cluster nearby(in the same segment). The virtual IP address is the IP address used when constructing an HA cluster in remote location(between different segments).

There are also two methods for configuring access to the business application using hostname. The virtual computer name resource is a resource that handles NetBIOS name on a NetBEUI network, and the dynamic DNS resource is a resource that handles host name on a TCP/IP network. In this article, both are referred to as functions that use host name to access the server on which the business application is operating.

The connection destination switching function on on-premises environment can be used in the following ways depending on the network environment that can be prepared.

  • Use virtual IP address in the same segment
    -> Floating IP resource
  • Network segments are different and RIP is reachable between routers
    -> Virtual IP resource
  • Use virtual host name in the same segment or between different segments
    -> Dynamic DNS resource

Although a method of connecting by hostname in the same segment, both the virtual computer name resource and the dynamic DNS resource can be used, we recommend to use the dynamic DNS resource if a DNS server can be prepared. Because, TCP/IP is currently the mainstream network protocol used for communication between computers and It is becoming less common to use the NetBEUI (old protocol) that the virtual computer name resource uses. Please consider using the virtual computer name resource if a DNS server is not available.

There are also ways to switch the destination connections using something other than the EXPRESSCLUSTER's connection destination switching function(group resource). One method to connect via hostname is to register the hostname and floating IP address in the hosts file of the client etc. that becomes the connection source, and use it. There is also a method to switch the connection destination by executing a script from EXPRESSCLUSTER that rewrites the hosts file of all clients accessing the cluster servers. We will introduce these methods later.

In environments where neither method can be used, it is necessary to consider measures such as manually updating DNS records and client connection destinations.

2. HA Cluster Configuration Using EXPRESSCLUSTER's Switching the Connection Destination Function

Introducing an example HA cluster configuration when using each connection destination switching function.
Please refer to the characteristics of each configuration example below.

Each connection destination switching method can be used in combination with HA cluster configurations such as shared disk type, mirror disk type, and hybrid disk type.

[Reference]
popupDocumentation - Product Introduction
  • Presentation > EXPRESSCLUSTER X Product Introduction for Windows/Linux
  • -> 2. Key Advantages
  • -> Flexible-1: Supported Cluster Configuration

2.1 HA Cluster Configuration Using Floating IP Resources

This is a configuration that connects from the client to the HA cluster using a virtual IP address(floating IP) managed by EXPRESSCLUSTER. The IP address will be taken over in the same segment. The floating IP must be set to an address in the same subnet as the cluster servers.
Basically, it is used when constructing an HA cluster in a nearby area(in the same segment). Even if you place a server far away, it is possible to take over an IP address using a floating IP address, if you can build a LAN in the same segment using VPN.

The method for switching the connection destination sends an ARP broadcast to update the ARP table information of network devices such as switches. Therefore, in order to use the floating IP resource, it is necessary to prepare a network that allows broadcasting of ARP packets.

For details on the floating IP resource, please refer to the Reference Guide.

[Reference]
popupDocumentation - Manuals
  • EXPRESSCLUSTER X 5.2 > EXPRESSCLUSTER X 5.2 for Windows > Reference Guide
  • -> 3. Group resource details
  • -> 3.7 Understanding floating IP resources
  • EXPRESSCLUSTER X 5.2 > EXPRESSCLUSTER X 5.2 for Linux > Reference Guide
  • -> 3. Group resource details
  • -> 3.8 Understanding Floating IP resource

2.2 HA Cluster Configuration Using Virtual IP Resources

This is a configuration that connects from the client to the HA cluster using a virtual IP address(virtual IP) managed by EXPRESSCLUSTER. The IP address will be taken over between different segments. The virtual IP must be set to an address outside the network address range of the subnet to which the cluster servers belong.

The method for switching the connection destination sends RIP packets to update the routing information of network devices such as routers. Therefore, in order to use the virtual IP resource, the WAN must support dynamic routing and allow dynamic route changes using RIP.

For details on the virtual IP resource, please refer to the Reference Guide.

[Reference]
popupDocumentation - Manuals
  • EXPRESSCLUSTER X 5.2 > EXPRESSCLUSTER X 5.2 for Windows > Reference Guide
  • -> 3. Group resource details
  • -> 3.15 Understanding virtual IP resources
  • EXPRESSCLUSTER X 5.2 > EXPRESSCLUSTER X 5.2 for Linux > Reference Guide
  • -> 3. Group resource details
  • -> 3.9 Understanding virtual IP resources

2.3 HA Cluster Configuration Using Virtual Computer Name Resources

This is a configuration that connects from the client to the HA cluster using a virtual computer name. Available in the same segment. This is a group resource that can only be used in the Windows version of EXPRESSCLUSTER, and only Windows machine clients can connect to the cluster servers using the virtual computer name.

As a method for switching the connection destination, a packet is issued to register the NetBIOS virtual computer name when the virtual computer name is enabled in the cluster. Therefore, in order to use the virtual computer name resource, it is necessary to prepare a network that allows broadcast packets for registering NetBIOS virtual computer names.

To connect to the cluster server using a virtual computer name from a remote LAN, associate the virtual computer name with a floating IP address, and write the pair of virtual computer name and floating IP address in the client's LMHOSTS file. Additionally, if you do not want to associate a virtual computer name with a floating IP address, you will need to dynamically register the virtual computer name in DNS or set up a WINS server.

For details on the virtual computer name resource, please refer to the Reference Guide.

[Reference]
popupDocumentation - Manuals
  • EXPRESSCLUSTER X 5.2 > EXPRESSCLUSTER X 5.2 for Windows > Reference Guide
  • -> 3. Group resource details
  • -> 3.13 Understanding virtual computer name resources

2.4 HA Cluster Configuration Using Dynamic DNS Resources

This is a configuration that connects from the client to the HA cluster using a virtual host name (DNS name). Available in the same segment or between different segments.

When switching the connection destination, updates the DNS record on the dynamic DNS server by EXPRESSCLUSTER. A client can connect to the server on which the business application is operating using the same host name by querying the dynamic DNS server for the IP address of the server corresponding to the virtual host name to switch destination.

To use the dynamic DNS resource, you need to build a dynamic DNS server in advance. When using the dynamic DNS resource in the Windows version, only Active Directory can be used as the dynamic DNS server. When using the dynamic DNS resource in the Linux version, there are two types: with authentication and without authentication. In the with authentication, only a dynamic DNS server built using BIND9 can be used, and when using the without authentication, servers other than BIND9 can also be used.

For details on the dynamic DNS resource, please refer to the Reference Guide.

[Reference]
popupDocumentation - Manuals
  • EXPRESSCLUSTER X 5.2 > EXPRESSCLUSTER X 5.2 for Windows > Reference Guide
  • -> 3. Group resource details
  • -> 3.14. Understanding dynamic DNS resources
  • EXPRESSCLUSTER X 5.2 > EXPRESSCLUSTER X 5.2 for Linux > Reference Guide
  • -> 3. Group resource details
  • -> 3.13. Understanding Dynamic DNS resources

3. HA Cluster Configuration that Switching the Connection Destination by Virtual Hostname in Combination with Floating IP

Although limited to use in the same segment, there is also a method to switching the connection destination using virtual host name by combining them with the floating IP resource without using the virtual computer name resource or the dynamic DNS resource.

3.1 When Using Hosts File

This method is to register the floating IP resource in EXPRESSCLUSTER, and then setting the pair of virtual host name and floating IP in the hosts file of the client, etc. that will be the connection source. If there are multiple client PCs to connect to, you need to set the hosts file for all client PCs. By switching the floating IP address linked to the virtual host name by EXPRESSCLUSTER, the client can connect to the server on which the business application is operating using the virtual host name.

3.2 When Using DNS Server

This method is to register the floating IP resource in EXPRESSCLUSTER, and then setting the pair of virtual host name and floating IP in the DNS server. By switching the floating IP address linked to the virtual host name by EXPRESSCLUSTER, the client can connect to the server on which the business application is operating using the virtual host name.
Consider this method if you can prepare a DNS server, but it is difficult to dynamically update the DNS server using EXPRESSCLUSTER due to security restrictions, etc.

4. HA Cluster Configuration that Switching the Connection Destination by Virtual Hostname Using Script

4.1 HA Cluster Configuration that Switching the Connection Destination by Rewriting the Hosts File

In a Windows environment, this is a method to switching the connection destination by rewriting the hosts file.
By using WinRM to rewrite the hosts files of all clients accessing the HA cluster from EXPRESSCLUSTER, you can achieve a switch in the connection destination to the HA cluster. Consider this method when the four switching the connection destination functions(group resources) provided by EXPRESSCLUSTER cannot be used.

Please refer to the article below for details.

Conclusion

This time, we introduced the function and selection methods of switching the connection destination for HA cluster configuration on on-premise environments. Please refer to this article not only to select a connection destination switching method, but also to check in advance whether the method is compatible with the environment in which it will be installed.

If you consider introducing the configuration described in this article, you can perform a validation with the popuptrial module of EXPRESSCLUSTER. Please do not hesitate to contact us if you have any questions.