JP7209784B1 - Redundant system and redundant method - Google Patents

Abstract

The present invention enables switching on a server-by-server basis while using software that assumes switching on a process-by-process basis. A redundant system (100) includes a first server (10) operating in a master system and a second server (20) operating in a slave system. In the first server 10 and the second server 20, a processing unit, which is a process for realizing processing functions, and a switching unit, which is a process for realizing switching between the master system and the slave system, operate. The switching unit in the second server 20 causes the second server 20 to operate as the main system when at least one of the processing unit and the switching unit in the first server fails. [Selection drawing] Fig. 1

Description

The present disclosure relates to redundancy technology for performing switching on a server-by-server basis.

In terms of cost, there is a demand to migrate the software used in current systems from paid software to OSS (Open Source Software). For example, there is a demand to migrate a paid database (hereinafter referred to as DB) to an OSS DB.

Current systems operating on-premises are often switched over on a server-by-server basis. When OSS is used, there are cases where switching is performed on a process-by-process basis. As a result, the operation of current systems may have to be changed.

Patent Literature 1 describes a distributed system that switches to a standby system not for each server but for each business.

JP-A-9-293059

In the operation of switching by process, management becomes complicated. Therefore, in the case of a system operating on-premises, it may be desirable to switch on a server-by-server basis instead of switching on a process-by-process basis. However, if an OSS is selected from a cost standpoint and the selected OSS performs switching on a process-by-process basis, it is not possible to switch on a server-by-server basis.
An object of the present disclosure is to enable switching in units of servers while using software that assumes switching in units of processes.

The redundant system according to the present disclosure is
A redundant system comprising a first server operating as a master system and a second server operating as a slave system,
In the first server and the second server, a processing unit, which is a process for realizing processing functions, and a switching unit, which is a process for realizing switching between a master system and a slave system, operate,
The switching unit in the second server causes the second server to operate as a main system when at least one of the processing unit and the switching unit in the first server fails.

In the present disclosure, when a failure occurs in at least one of the processing unit and the switching unit in the first server operating as the main system, the second server is operated as the main system. As a result, even when the processing unit and the switching unit are realized by software that assumes switching on a per-process basis, switching on a server-by-server basis is possible.

1 is a configuration diagram of a redundant system 100 according to Embodiment 1; FIG. 2 is a configuration diagram of a first server 10 according to Embodiment 1. FIG. 2 is a configuration diagram of a second server 20 according to Embodiment 1. FIG. FIG. 4 is a schematic explanatory diagram of processing of the redundancy system 100 according to the first embodiment; FIG. FIG. 4 is a schematic explanatory diagram of processing of the redundancy system 100 according to the first embodiment; FIG. 4 is a flowchart of first failure processing according to the first embodiment; 4 is a flowchart of second failure processing according to the first embodiment; 9 is a flowchart of third failure processing according to the first embodiment; 10 is a flowchart of fourth failure processing according to the first embodiment; FIG. 4 is an explanatory diagram of the effects of the redundant system 100 according to the first embodiment; FIG. 4 is an explanatory diagram of the effects of the redundant system 100 according to the first embodiment;

Embodiment 1.
*** Configuration description ***
A configuration of a redundant system 100 according to the first embodiment will be described with reference to FIG.
A redundant system 100 includes a first server 10 , a second server 20 , and an application server 30 .
The first server 10 and the second server 20 are servers realizing the same function. In Embodiment 1, the first server 10 and the second server 20 are assumed to be database servers that implement database functions. The application server 30 uses a virtual IP (Internet
Protocol) address is used to access whichever of the first server 10 and the second server 20 operates in the main system. In the first embodiment, in the initial state, the first server 10 operates as a main system, and the second server 20 operates as a subordinate system.

A configuration of the first server 10 according to the first embodiment will be described with reference to FIG.
The first server 10 is a computer.
The first server 10 includes hardware including a processor 11 , a memory 12 , a storage 13 and a communication interface 14 . The processor 11 is connected to other hardware via signal lines and controls these other hardware.

In the first server 10, a processing unit 111, a switching unit 112, and an internal monitoring unit 113 operate as functional components. The switching unit 112 includes an external monitoring unit 114 , a switching execution unit 115 and a failure detection unit 116 . The function of each functional component of the first server 10 is realized by software.
The storage 13 stores a program that implements the function of each functional component of the first server 10 . This program is read into the memory 12 by the processor 11 and executed by the processor 11 . Thereby, the function of each functional component of the first server 10 is realized.

An operation script 131 is stored in the storage 13 . The operational script 131 includes a stop script 132 , a promotion script 133 and a synchronization release script 134 .

The configuration of the second server 20 according to the first embodiment will be described with reference to FIG.
The second server 20 is a computer.
The second server 20 includes hardware including a processor 21 , a memory 22 , a storage 23 and a communication interface 24 . The processor 21 is connected to other hardware via signal lines and controls these other hardware.

In the second server 20, a processing unit 211, a switching unit 212, and an internal monitoring unit 213 operate as functional components. The switching unit 212 includes an external monitoring unit 214 , a switching execution unit 215 and a failure detection unit 216 . The function of each functional component of the second server 20 is realized by software.
The storage 23 stores a program that implements the function of each functional component of the second server 20 . This program is read into the memory 22 by the processor 21 and executed by the processor 21 . Thereby, the function of each functional component of the second server 20 is realized.

An operation script 231 is stored in the storage 23 . The operational script 231 includes a stop script 232 , a promotion script 233 and a synchronization cancellation script 234 .

The processing units 111 and 211 are processes that implement processing functions. In Embodiment 1, the processing function is a database function. The processing function is not limited to the database function, and may be other functions such as functions for realizing some kind of business processing. The switching unit 112 and the switching unit 212 are processes for realizing switching between the main system and the slave system for the processing units 111 and 211 . The internal monitoring unit 113 and the internal monitoring unit 213 are processes that monitor the switching unit 112 and the switching unit 212, respectively.
The processing unit 111 and the switching unit 112, and the processing unit 211 and the switching unit 212 are realized by OSS. In Embodiment 1, the processing units 111 and 211 are implemented by PostgreSQL, and the switching units 112 and 212 are implemented by pgpool. The internal monitoring unit 113 and the internal monitoring unit 213 may be realized by OSS or may be realized by other software.

The processors 11 and 21 are ICs (Integrated Circuits) that perform processing. As a specific example, the processors 11 and 21 are CPUs (Central
Processing Unit), DSP (Digital Signal Processor), and GPU (Graphics Processing Unit).

The memories 12 and 22 are storage devices that temporarily store data. Specific examples of the memories 12 and 22 are SRAM (Static Random Access Memory) and DRAM (Dynamic Random Access Memory).

The storages 13 and 23 are storage devices that store data. Specific examples of the storages 13 and 23 are HDDs (Hard Disk Drives) and SSDs (Solid State Drives). The storages 13 and 23 are SD (registered trademark, Secure Digital) memory cards, CF (Compact Flash, registered trademark), NAND flashes, flexible disks, optical disks, compact disks, Blu-ray (registered trademark) disks, DVDs (Digital Versatile Disks). ) may be a portable recording medium.

Communication interfaces 14 and 24 are interfaces for communicating with external devices. The communication interfaces 14 and 24 are, for example, Ethernet (registered trademark) and USB (Universal Serial Bus) ports.

Only one processor 11 was shown in FIG. However, there may be a plurality of processors 11, and the plurality of processors 11 may cooperate to execute programs that implement each function. Similarly, only one processor 21 was shown in FIG. However, there may be a plurality of processors 21, and the plurality of processors 21 may cooperate to execute programs that implement each function.

***Description of operation***
The operation of the redundant system 100 according to the first embodiment will be described with reference to FIGS. 4 to 9. FIG.
The operating procedure of the redundancy system 100 according to the first embodiment corresponds to the redundancy method according to the first embodiment. Also, a program that realizes the operation of the redundancy system 100 according to the first embodiment corresponds to the redundancy program according to the first embodiment.

The operation of the redundant system 100 includes first failure processing when a failure occurs in the switching unit 112 of the first server 10, second failure processing when a failure occurs in the processing unit 111 of the first server 10, It is divided into third failure processing when a failure occurs in the switching unit 212 of the second server 20 and fourth failure processing when a failure occurs in the processing unit 211 of the second server 20 .

An overview of the processing of the redundant system 100 according to the first embodiment will be described with reference to FIGS. 4 and 5. FIG.
The processing unit 111 receives an instruction from the switching unit 112 or the switching unit 212 as to whether to operate in the master system or in the slave system, and performs switching. Similarly, the processing unit 211 receives an instruction from the switching unit 212 or the switching unit 112 as to whether to operate in the master system or in the slave system, and switching is performed. Also, the switching unit 112 switches between operating in the main system and operating in the subordinate system. Similarly, the switching unit 212 switches between operating in the master system and operating in the slave system.
As shown in FIG. 4, the application server 30 switches between the processing unit 111 and the processing unit 211 operating in the main system via the switching unit 112 and the switching unit 212 operating in the main system. to access.

Here, the processing unit 111 switches between operating in the master system and operating in the slave system independently of the switching unit 112 . Similarly, the processing unit 211 switches between operating in the master system and operating in the slave system independently of the switching unit 212 . Also, the switching unit 112 switches between operating in the master system and operating in the slave system independently of the processing unit 111 . Similarly, the switching unit 212 switches between operating in the master system and operating in the slave system independently of the processing unit 211 .
That is, the processing unit 111 and the switching unit 112, and the processing unit 211 and the switching unit 212 perform switching between the master system and the slave system for each process. Such controls are implemented in PostgreSQL and pgpool.

Therefore, without any control, the application server 30 may access the processing unit 111 via the switching unit 212 as shown in FIG. In the redundant system 100 according to the first embodiment, the application server 30 accesses the processing unit 111 via the switching unit 112 or accesses the processing unit 211 via the switching unit 212. control so that That is, in the redundant system 100 according to the first embodiment, both the processing unit 111 and the switching unit 112 are operating in the main system, and both the processing unit 211 and the switching unit 212 are operating in the main system. Control to be either the state where
When both the processing unit 111 and the switching unit 112 are operating as the main system, it is said that the first server 10 is operating as the main system. Similarly, when both the processing unit 211 and the switching unit 212 are operating as the main system, it is said that the second server 20 is operating as the main system.

The first failure processing according to the first embodiment will be described with reference to FIG.
A failure occurs in the switching unit 112 of the first server 10 (step S10).

(Step S11: first failure detection process)
The switching unit 212 of the second server 20 detects that the switching unit 112 of the first server 10 has failed. When the switching unit 212 detects that the switching unit 112 has failed, it operates as a main system.
Specifically, the external monitoring unit 114 in the switching unit 112 of the first server 10 and the external monitoring unit 214 in the switching unit 212 of the second server 20 periodically transmit information informing each other of the status. communicating. Here, the external monitoring unit 114 transmits first state information indicating the states of the processing unit 111 and the switching unit 112 to the switching unit 212 , and the external monitoring unit 214 transmits first state information indicating the states of the processing unit 211 and the switching unit 212 . 2-state information is transmitted to the switching unit 112 . When a failure occurs in the switching unit 112, the external monitoring unit 114 stops transmitting the first state information. The external monitoring unit 214 determines that a failure has occurred in the switching unit 112 when the transmission of the first state information is stopped for the reference time or longer.
The first failure detection process is realized by a function pre-implemented in pgpool.

(Step S12: stop processing)
The switching unit 212 of the second server 20 activates the stop script 232 in the operation script 231 to stop the processing unit 111 of the first server 10 .
Specifically, the stop script 232 is a script that issues a stop command to stop the program. The switching execution unit 215 in the switching unit 212 of the second server 20 designates the processing unit 111 of the first server 10 and stops the processing unit 111 by executing the stop script 232 .
When the processing unit 111 and the processing unit 211 are realized by PostgreSQL, the stop command for stopping the processing unit 111 or the processing unit 211 is "${PGPATH%/}/pg_ctl stop-D${PGDATA}. ${PGPATH} is the path of the folder of the database function to be stopped, so here, ${PGPATH} is the path of the folder in which the program of processing unit 111 is stored.

(Step S13: second failure detection process)
The switching unit 212 of the second server 20 detects that the processing unit 111 of the first server 10 has failed.
Specifically, the failure detection unit 216 in the switching unit 212 of the second server 20 monitors the state of the processing unit 111 of the first server 10 . The failure detection unit 216 detects that a failure has occurred in the processing unit 111 when the processing unit 111 is stopped in the process of step S12.
The second failure detection process is realized by a function pre-implemented in pgpool.

(Step S14: promotion process)
The switching unit 212 of the second server 20 activates the promotion script 233 in the operation script 231 to promote the processing unit 211 of the second server 20 to the main system.
Specifically, the promotion script 233 is a script that issues a promotion command for promoting the processing unit 111 or the processing unit 211 to the main system. The switching execution unit 215 in the switching unit 212 of the second server 20 designates the processing unit 211 of the second server 20 and executes the promotion script 233 to promote the processing unit 211 to the main system.
When the processing unit 111 and the processing unit 211 are realized by PostgreSQL, the promotion command is "${PGPATH%/}/pg_ctl"promote-D"${new_master_node_pgdata}". ${new_master_node_pgdata} is the folder path of the database function to promote. Therefore, here, ${new_master_node_pgdata} is the path of the folder in which the program of the processing unit 211 is stored.

In the processing of step S11, the switching unit 212 becomes the main system, and in the processing of step S14, the processing unit 211 becomes the main system. As a result, the second server 20 enters a state of operating as the main system. In other words, the server operating as the main system is switched from the first server 10 to the second server 20 .
When the processing function is a database, the synchronous processing is realized by a pre-implemented function (PostgreSQL), synchronizing the master data while the slave system is running. If it is a slave system, it can only read, but by executing the promotion script, it will be promoted to the master system, so it will be possible to write in addition to reading.

The second failure processing according to the first embodiment will be described with reference to FIG.
A failure occurs in the processing unit 111 of the first server 10 (step S20).

(Step S21: first failure detection process)
The switching unit 112 of the first server 10 detects that the processing unit 111 of the first server 10 has failed.
Specifically, the failure detection unit 116 in the switching unit 112 of the first server 10 monitors the state of the processing unit 111 of the first server 10 . The failure detection unit 116 detects that a failure has occurred in the processing unit 111 when the processing unit 111 stops or the like.
The first failure detection process is realized by a function pre-implemented in pgpool.

At this time, the switching unit 212 of the second server 20 also detects that the processing unit 111 of the first server 10 has failed, similarly to the switching unit 112 of the first server 10 .

(Step S22: stop processing)
The switching unit 112 of the first server 10 activates the stop script 132 in the operation script 131 to stop the switching unit 112 of the first server 10 .
Specifically, the stop script 132 is a script that issues a stop command to stop the program, like the stop script 232 . The switching execution unit 115 in the switching unit 112 of the first server 10 designates the switching unit 112 of the first server 10 and stops the switching unit 112 by executing the stop script 132 .

(Step S23: second failure detection process)
The switching unit 212 of the second server 20 detects that the switching unit 112 of the first server 10 has failed. When the switching unit 212 detects that the switching unit 112 has failed, it operates as a main system.
Specifically, since the switching unit 112 is stopped in the process of step S22, transmission of the first state information from the external monitoring unit 114 in the switching unit 112 is stopped. The external monitoring unit 214 in the switching unit 212 of the second server 20 determines that a failure has occurred in the switching unit 112 when the transmission of the first state information is interrupted for the reference time or longer.
The second failure detection process is realized by a function pre-implemented in pgpool.

(Step S24: promotion process)
The switching unit 212 of the second server 20 activates the promotion script 233 in the operation script 231 to promote the processing unit 211 of the second server 20 to the main system, as in the process of step S14 in FIG.

In the processing of step S23, the switching unit 212 becomes the main system, and in the processing of step S24, the processing unit 211 becomes the main system. As a result, the second server 20 enters a state of operating as the main system. That is, the server operating as the main system is switched from the first server 10 to the second server 20 .

The third failure processing according to the first embodiment will be described with reference to FIG.
A failure occurs in the switching unit 212 of the second server 20 (step S30).

(Step S31: First failure detection process)
The internal monitoring unit 213 of the second server 20 detects that the switching unit 212 of the second server 20 has failed.
Specifically, the internal monitoring unit 213 monitors the state of the switching unit 212 . The internal monitoring unit 213 detects that a failure has occurred in the switching unit 212 when the switching unit 212 stops.

(Step S32: stop processing)
The internal monitoring unit 213 of the second server 20 activates the stop script 232 in the operation script 231 to stop the processing unit 211 of the second server 20 .
Specifically, the internal monitoring unit 213 of the second server 20 stops the processing unit 211 by specifying the processing unit 211 of the second server 20 and executing the stop script 232 .

(Step S33: Second failure detection process)
The switching unit 112 of the first server 10 detects that the processing unit 211 of the second server 20 has failed.
Specifically, when a failure occurs in the switching unit 212 , the second status information is no longer transmitted from the external monitoring unit 214 . The external monitoring unit 114 in the switching unit 112 of the first server 10 determines that a failure has occurred in the switching unit 212 when the transmission of the second state information is interrupted for the reference time or longer.
The second failure detection process is realized by a function pre-implemented in pgpool.

(Step S34: Synchronization Release Processing)
The switching unit 112 of the first server 10 activates the synchronization release script 134 in the operation script 131 to stop data synchronization with the processing unit 211 of the second server 20 .
Specifically, the synchronization cancellation script 134 is a script that stops synchronization of data between the processing unit 111 of the first server 10 and the processing unit 211 of the second server 20 . As a premise, data update information is transmitted from one of the processing units 111 and 211 operating in the master system to the one operating in the slave system, and data synchronization is performed. This is a pre-implemented feature in PostgreSQL. The switching unit 112 of the first server 10 stops data synchronization by specifying the processing unit 211 of the second server 20 and executing the synchronization release script 134 .

In the processing of step S32, the processing unit 211 is stopped in addition to the switching unit 212 in which the failure has occurred. As a result, the processing of the second server 20 is stopped.

A fourth failure process according to the first embodiment will be described with reference to FIG.
A failure occurs in the processing unit 211 of the second server 20 (step S40).

(Step S41: First failure detection process)
The switching unit 212 of the second server 20 detects that the processing unit 211 of the second server 20 has failed.
Specifically, the failure detection unit 216 in the switching unit 212 of the second server 20 monitors the state of the processing unit 211 of the second server 20 . The failure detection unit 216 detects that a failure has occurred in the processing unit 211 when the processing unit 211 stops.
The first failure detection process is realized by a function pre-implemented in pgpool.

At this time, the switching unit 112 of the first server 10 also detects that the processing unit 211 of the second server 20 has failed, similarly to the switching unit 212 of the second server 20 .

(Step S42: stop processing)
The switching unit 212 of the second server 20 activates the stop script 232 in the operation script 231 to stop the switching unit 212 of the second server 20 .
Specifically, the switching execution unit 215 in the switching unit 212 of the second server 20 stops the switching unit 212 by specifying the switching unit 212 of the second server 20 and executing the stop script 232 .

In the processing of step S42, the switching unit 212 is stopped in addition to the processing unit 211 in which the failure has occurred. As a result, the processing of the second server 20 is stopped.

(Step S43: Synchronization Release Processing)
The switching unit 112 of the first server 10 detects the failure of the processing unit 211 . Then, the switching unit 112 of the first server 10 activates the synchronization cancellation script 134 in the operation script 131 to stop data synchronization with the processing unit 211 of the second server 20 .

*** Effect of Embodiment 1 ***
As described above, the redundant system 100 according to the first embodiment can implement switching in units of servers using software that performs switching in units of processes. As a result, for example, when the software is OSS, it is possible to prevent complication of operation by switching on a server-by-server basis while keeping costs down.

As shown in FIG. 10, if a redundant database system is realized simply by using PostgreSQL and pgpool, switching will be performed on a process-by-process basis. FIG. 10 shows a case where a failure occurs in pgpool of server #1 while PostgreSQL and pgpool of server #1 are operating in the main system. When a failure occurs in the pgpool of server #1, the pgpool of server #2 switches over to the main system. However, PostgreSQL on server #1 is still running on the main system. Therefore, the application server 30 accesses PostgreSQL of server #1 via pgpool of server #2.
On the other hand, as shown in FIG. 11, in the redundant system 100 according to the first embodiment, when a failure occurs in pgpool of server #1, PostgreSQL of server #1 is stopped, and PostgreSQL of server #2 and pgpool switches to the principal. As a result, the application server 30 accesses PostgreSQL of server #2 via pgpool of server #2.

6, the switching unit 212 of the second server 20 stops the processing unit 111 when it detects that the switching unit 112 of the first server 10 has failed. .
If the switching unit 112 of the first server 10 detects that a failure has occurred in the processing unit 111 of the first server 10, the switching unit 112 stops itself as in the second failure processing described using FIG. do. After that, the switching unit 212 of the second server 20 performs promotion processing to the main system for the processing unit 211 .
As in the third failure process described using FIG. stop. After that, the switching unit 112 causes the processing unit 111 to stop data synchronization.
As in the fourth failure process described with reference to FIG. 9, when the switching unit 212 of the second server 20 detects that a failure has occurred in the processing unit 211 of the second server 20, the switching unit 212 itself Stop. After that, the switching unit 112 causes the processing unit 111 to stop data synchronization.
As described above, in this embodiment, when a failure is detected in a process of the first server 10 or the second server 20, the other process on the same server is stopped. This enables switching on a server-by-server basis.

Describe operational complexity.
Here, it is assumed that the system is running on-premises and operated by the user. Since operation is performed on the user side, the primary response in the event of a failure is performed on the user side.
When performing switching on a server-by-server basis, the user specifies which server is in trouble, and responds by, for example, restarting the specified server. On the other hand, when the process switching is performed in units of processes, the user needs to specify which process of which server is causing the failure. Then, it is necessary to take measures such as restarting the specified process. It may be difficult for the user to identify the failing process. It may also be difficult to respond by restarting the process.
In this way, when switching is performed on a process-by-process basis, the operation becomes complicated, and it may be difficult for the user to take action.

***Other Configurations***
<Modification 1>
In the first embodiment, the processing functions realized by the processing units 111 and 211 are database functions. However, the processing functions realized by the processing units 111 and 211 are not limited to database functions.
For example, multiple application servers 30 may be used to distribute the load. In this case, the processing functions realized by the processing units 111 and 211 may be functions of the application server 30 . Even if the processing function is the function of the application server 30, in principle, switching in units of servers can be realized by using the OSS that performs switching in units of processes by the processing described in the first embodiment. However, in step S42 of FIG. 9, it is necessary to stop synchronization of session information between functions of the application server 30 instead of synchronization of data between databases.

The embodiments and modifications of the present disclosure have been described above. Some of these embodiments and modifications may be combined and implemented. Also, any one or some may be partially implemented. It should be noted that the present disclosure is not limited to the above embodiments and modifications, and various modifications are possible as necessary.

100 redundant system, 10 first server, 11 processor, 12 memory, 13 storage, 14 communication interface, 15 electronic circuit, 111 processing unit, 112 switching unit, 113 internal monitoring unit, 114 external monitoring unit, 115 switching execution unit, 116 failure detection unit, 131 operation script, 132 stop script, 133 promotion script, 134 synchronization release script, 20 second server, 21 processor, 22 memory, 23 storage, 24 communication interface, 25 electronic circuit, 211 processing unit, 212 switching 213 internal monitoring unit 214 external monitoring unit 215 switching execution unit 216 failure detection unit 231 operation script 232 stop script 233 promotion script 234 synchronization release script 30 application server.

Claims (7)

A redundant system comprising a first server operating as a master system and a second server operating as a slave system,
In the first server and the second server, a processing unit, which is a process for realizing processing functions, and a switching unit, which is a process for realizing switching between a master system and a slave system, operate,
the switching unit in the second server causes the second server to operate as a main system when a failure occurs in at least one of the processing unit and the switching unit in the first server ;
The switching unit in the second server causes the second server to operate as a main system by stopping the processing unit in the first server when a failure of the switching unit in the first server is detected. redundant system. The switching unit in the first server stops when a failure of the processing unit in the first server is detected,
2. When the switching unit in the first server stops, the switching unit in the second server detects a failure of the switching unit in the first server and causes the second server to operate as a main system. The redundant system described in . In the second server, an internal monitoring unit, which is a process for monitoring the state of the switching unit in the second server, operates;
3. The redundancy system according to claim 1 , wherein the internal monitoring unit in the second server stops the processing unit in the second server when detecting a failure in the switching unit in the second server. 4. The method according to any one of claims 1 to 3 , wherein the switching unit in the second server issues a promotion command to the main system to the processing unit in the second server when operating the second server as the main system. The redundancy system according to any one of items 1 and 2. the processing function is a database function;
The switching unit in the second server stops when a failure of the database function in the second server is detected,
5. Any one of claims 1 to 4 , wherein the switching unit in the first server stops synchronization of data with the database function in the first server when a failure in the database function in the second server is detected. or the redundant system according to item 1. the processing function is an application server function;
When a failure of the application server function of the second server is detected, the switching unit of the second server stops synchronization of the session information with the application server function of the first server, and then stops. The redundancy system according to any one of claims 1 to 4 . A redundancy method in a redundant system comprising a first server operating as a master system and a second server operating as a slave system,
In the first server and the second server, a processing unit, which is a process for realizing processing functions, and a switching unit, which is a process for realizing switching between a master system and a slave system, operate,
When at least one of the processing unit and the switching unit in the first server fails, the switching unit in the second server causes the second server to operate as a main system ;
When a failure of the switching unit in the first server is detected, the switching unit in the second server stops the processing unit in the first server, thereby causing the second server to operate as a main system. redundancy method.

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