JP2009237835A - Web server system and load distribution method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Web server system and a load distribution method for distributing loads to Web servers with light loads, without having to measure the operating situations of other Web servers. <P>SOLUTION: Each Web server 1A, 1B, 1C includes a shared data storage unit 33 storing shared static content among each Web server 1A, 1B, 1C; an operation information giving and receiving unit 36, transmitting and receiving operation information consisting of past load information of each Web server and operation schedule information from monitor control unit 35 among each Web server in a fixed time zone; an operation information accumulation unit 34 accumulating the operation information; a load estimation unit 37, estimating a load on each Web server in the reception of transmission requests, on the basis of the operation information, when receiving from a client terminal 6, transmission requests of Web pages described in a Web description language and in which the link destinations are pasted; and a Web page change unit 38 rewriting the link destinations in Web pages into Web servers with lighter loads, on the basis of the estimation result of the loads. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a Web server system and a load distribution method.

  Conventionally, as shown in FIG. 3, the control terminal 12 and the monitoring terminal 13 such as lighting equipment and air-conditioning equipment respectively installed in the respective areas A, B, C... And the areas A, B, C. .., And the integrated controllers 11A, 11B, 11C... For monitoring or controlling each terminal connected to the terminals (the control terminal 12 and the monitoring terminal 13) in the local area via the local network 14, and a plurality of integrated controllers 11A. , 11B, 11C,... Are connected via a communication network 15, and a central monitoring system comprising a central monitoring panel 16 that monitors the operation state of the entire system and sets the operation schedule of terminals installed in each area. Is provided.

  In the system shown in FIG. 3, since the integrated controllers 11A, 11B, 11C,... Do not require a graphical user interface (GUI) function, a control device incorporating a network communication function is used. Has a smaller number of shipments than the integrated controllers 11A, 11B, 11C... And terminals (control terminal 12 or monitoring terminal 13) and requires a GUI function, and therefore has a communication function with the integrated controllers 11A, 11B, 11C. Most of them consisted of dedicated computers. Therefore, it was difficult to ensure long-term reliability, and it was very expensive because the cost (initial cost and maintenance cost) for ensuring long-term reliability had to be added to the price. .

  Therefore, in the central monitoring system as shown in FIG. 3, the integrated controllers 11A, 11B, 11C,... Are equipped with a Web server function, and a general browser software is incorporated into each integrated controller 11A, 11B, 11C,. A Web server system is proposed in which requests are sent and each integrated controller 11A, 11B, 11C... Analyzes an HTTP request and performs desired processing (terminal control or monitoring). The cost of the entire system is reduced by eliminating this.

  In such a Web server system, a small-scale system with a small number of integrated controllers requires only a few administrators and the access frequency to the integrated controller (Web server) may be low. However, there are several integrated controllers. In a medium-sized or larger system (for example, for a tenant building) installed from several to several, there may be a plurality of managers for each area (for example, tenant) as well as for the entire building. In such a system, the access frequency to the Web server may be too high from the manager of the entire building or the manager of each area, and as a result, the HTTP request cannot be processed within the time specified by the system. Or an important notification process such as an alarm notification may time out and the administrator may not be notified.

  By the way, other integrated controllers cannot process HTTP requests targeted by a specific integrated controller such as control requests, but images, HTML (Hyper Text Markup Language), scripts, CSS (Cascading Style Sheets), etc. Since static content (content that does not change over time) may be distributed from any Web server, distribution processing is performed by a plurality of Web servers in order to prevent an excessive load on a specific Web server. Are distributed and processed. For example, in the Web server system as shown in FIG. 4, the load balancer 21 allocates an HTTP request sent from the client terminal 20 via the hub 23 to the subordinate server group 22, so that the load on the specific Web server 24 is excessive. Is prevented. However, in this Web server system, a load balancer 21 and a DNS server (not shown) are necessary to distribute the load on the Web server 24, and the introduction cost of the entire system increases. Therefore, each Web server 24 is independent. In particular, a system that distributes the load is more desirable. As such a system, for example, there is a system that employs a proxy-type load distribution method.

  FIG. 5A is an explanatory diagram for explaining a proxy-type load distribution method. This system includes a control terminal 2 and a monitoring terminal 3 installed in each area A, B..., And a Web server 1A that monitors or controls the terminals 2 and 3 in each area A, B. , 1B... And Web servers 1A, 1B... Are connected via a communication network 5, and are configured with client terminals 6 that monitor the operation state of the entire system and set the operation schedule of terminals installed in each area. Has been. Here, when the client terminal 6 makes an HTML file acquisition request to the Web server 1A (a in the figure), an HTML file describing a static content link destination is returned from the Web server 1A to the client terminal 6. (B in the figure). After that, when the client terminal 6 sends a distribution request (HTTP request) of static content with a link destination in the HTML file to the Web server 1A (c in the figure), the Web server 1A receives the request from the client terminal 6. Is distributed to the Web server 1B (d in the figure). When the web server 1A receives the static content returned from the web server 1B (e in the figure), the web server 1A returns the received static content to the client terminal 6 (f in the figure), and responds to the HTTP request. The process ends. As described above, in the proxy-type load balancing method, between the time when the client terminal 6 requests acquisition of the HTML file and the time when the static content is received, the Web server 1A and the client terminal 6 or the Web server 1B are connected. Although communication is performed six times, a controller that does not have a secondary storage device such as a hard disk and has a built-in Web server has a low upper limit of the number of processes and the number of simultaneous connections. There is a problem that the number of connections cannot be reduced by a proxy-type load balancing method in which a certain Web server makes a proxy response to another Web server. Further, when the transfer destination Web server 1B does not respond, there is a problem that the connection is left until the timeout occurs.

  Therefore, a method of reducing the load of a desired Web server by rewriting the link in the HTML file returned to the client terminal 6 instead of the proxy type load distribution method (see, for example, Patent Document 1).

  FIG. 5B is an explanatory diagram of a load distribution method by link rewriting. When the client terminal 6 makes an HTML file acquisition request to the Web server 1A (g in the figure), the Web server 1A returns a response to the client terminal 6. The link destination of the static content described in the HTML file to be rewritten is changed to another Web server, and then this HTML file is returned to the Web server 1B (h in the figure). Thereafter, the client terminal 6 transmits a static content distribution request (HTTP request) in which the link destination is pasted in the HTML file acquired from the Web server 1A to the Web server 1B (i in the figure), and the Web server 1B. Returns the requested static content to the client terminal 6 (j in the figure).

As described above, if the link in the HTML file returned to the client terminal 6 is rewritten, the number of connections to the Web server 1A is reduced, and the load on the Web server 1A can be reduced.
JP 2002-278823 A (paragraphs [0019]-[0030] and FIG. 1)

  By the way, in the load distribution method by link rewriting described above, when the Web server 1A changes the link destination to another Web server, the method of allocating the change destination Web server is shown in Table 1 like the existing load balancer. Four methods are conceivable.

  Here, in the method 1 shown in Table 1, there is a problem that links are allocated in a predetermined order, and the load status of the allocation Web server is not considered at all. In the methods 2, 3, and 4 in Table 1, it is necessary to detect the operation status of another Web server at the time of rewriting the link. Such information can be easily obtained or predicted in a Web server system using a load balancer, but in a Web server system without a load balancer for cost reduction, the operation of other Web servers is possible. There is a problem that the situation cannot be acquired, and the process itself for acquiring the operation status of another Web server at the time of rewriting the link increases the load on the Web server or the network.

  The present invention has been made in view of the above problems, and the object of the present invention is to distribute the load to a Web server with a small load without measuring the operation status of another Web server. To provide a Web server system and a load distribution method.

  In order to achieve the above object, according to the first aspect of the present invention, there is provided a Web server system in which a plurality of Web servers providing Web services and client terminals are connected via a communication network. At least a monitoring control unit that monitors or controls the terminal, a shared data storage unit that stores static content common to each Web server, past load information of each Web server, and operation schedule information by the monitoring control unit An operation information exchange unit for exchanging operation information between Web servers in a predetermined time zone, an operation information accumulation unit for accumulating acquired operation information, and a link destination of the static content described in the Web description language. When a transmission request for a received Web page is received from a client terminal, the load on each Web server when the transmission request is received A load estimation unit that estimates based on the operation information, and a Web page change unit that changes the Web page to rewrite a link destination in the Web page to a Web server having a lower load based on an estimation result of the load estimation unit; It is provided with.

  According to a second aspect of the present invention, in the first aspect of the present invention, the operation information sending / receiving unit has congestion time information indicating a time period in which the load is relatively large compared to other time periods, and is either When the operation schedule information is changed in the Web server, the changed difference information is exchanged between the Web servers.

  According to a third aspect of the invention, in the first or second aspect of the invention, the web page changing unit analyzes the load information of each web server estimated by the load estimating unit and browser software installed in the client terminal analyzes the web page. At this point, a processing instruction for executing processing for changing the link destination of static content on the client terminal side based on the load information is written on the Web page.

  According to a fourth aspect of the present invention, in the Web server according to any one of the first to third aspects, when the Web server detects an abnormal state of the terminal to be monitored or controlled, the Web server sends the abnormal information for notifying the abnormal state to another Web server. And an abnormal information transmitting / receiving unit that receives abnormal information from another Web server, and the Web page changing unit is configured to notify the Web server that has notified the abnormal state when changing the link destination in the Web page. It is excluded from the target of the change destination.

  The invention of claim 5 is a load distribution method of a Web server system in which a plurality of Web servers providing Web services and client terminals are connected via a communication network, and includes past load information of each Web server and A step of transferring operation information including at least operation schedule information by the monitoring control unit between Web servers in a predetermined time zone, and a step of storing operation information acquired from other Web servers in the operation information storage unit by the Web server; When the Web server receives a transmission request of a Web page described in the Web description language and attached with a static content link destination from the client terminal, the reception is performed based on the operation information stored in the operation information storage unit. Estimating the load on each Web server, and the Web server calculating the load on each Web server Based on the boss was the result, characterized in that it comprises a step of changing the Web page to rewrite the destination in the Web page to the lower Web server load.

  According to the first aspect of the present invention, the operation information transfer unit of each Web server transmits and receives operation information including at least the past load information of each Web server and the operation schedule information of the monitoring control unit in a predetermined time zone, When receiving a Web page transmission request from the client terminal, the load estimation unit estimates the load of each Web server at the time of reception based on the operation information, and thus a load balancer that measures the load status of each Web server in real time. Even when there is no Web server system, it is possible to realize a Web server system capable of estimating the load of each Web server at the time when the transmission request is received. Since the Web page changing unit changes the Web page in order to rewrite the link destination in the Web page to a Web server having a lower load based on the load estimation result, the client terminal links to the Web page. When requesting transmission of static content first, the transmission request is transmitted to the changed linked web server, and the web server can distribute the load to the web server that is estimated to have a low load. A system can be realized.

  According to the invention of claim 2, when the operation schedule information is changed in any of the Web servers, it is necessary to exchange the changed schedule information between the Web servers. By giving and receiving between, traffic increase can be suppressed. Further, when the operation information is changed, the load on each Web server can be estimated based on the changed operation information by exchanging the difference information of the operation information between the Web servers. Can be reliably estimated.

  According to the invention of claim 3, the Web page changing unit writes the load information and processing instruction of each Web server estimated by the load estimating unit on the Web page, and the Web page is mounted on the client terminal. Since the link destination of the static content is changed based on the load information written on the Web page on the client terminal side when the browser software analyzes, the processing for changing the link destination of the static content is performed on the client terminal. The processing of the Web server can be further reduced.

  According to the invention of claim 4, since the Web server that has notified the abnormal state is removed from the change target when the link destination in the Web page is changed, the terminal to be monitored or controlled is in the abnormal state. It is possible to reduce the load on the Web server, and to reliably perform processing corresponding to the abnormal state (for example, processing for notifying the abnormal state).

  According to the invention of claim 5, the operation information including at least the past load information of each Web server and the operation schedule information of the monitoring control unit is exchanged between the Web servers in a predetermined time zone and accumulated in the operation information storage unit. When each Web server receives a Web page transmission request from the client terminal, the load on each Web server is estimated based on the accumulated operation information. Even when there is no load balancer that measures the situation in real time, it is possible to estimate the load of each Web server at the time when the transmission request is received. Since each Web server changes the Web page in order to rewrite the link destination in the Web page to a Web server with a lower load based on the load estimation result, the client terminal links to the link destination in the Web page. When requesting transmission of static content, the transmission request is transmitted to the changed link destination Web server, and the load can be distributed to the Web server estimated to have a low load.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
A first embodiment of the present invention will be described with reference to FIGS. 1 and 2. As shown in FIG. 1, the Web server system according to the present embodiment includes a control terminal 2 and a monitoring terminal such as an illumination device and an air conditioner installed in each area A, B, C,. 3 and a web server that is installed in each of the areas A, B, C,... And the terminals (control terminal 2 and monitoring terminal 3) in its own area are connected via the local network 4 to monitor or control each terminal. 1A, 1B, 1C... And a client terminal 6 connected to each Web server 1A, 1B, 1C... Via a communication network 5 such as the Internet. Each Web server 1A, 1B, 1C,... Is pre-registered with global addresses of all Web servers installed in the same building (a Web server sharing static content described later). The servers 1A, 1B, 1C... Can communicate with each other via the communication network 5.

  Each of the Web servers 1A, 1B, 1C,... Is configured by a controller that has a function of monitoring or controlling subordinate terminals (the control terminal 2 and the monitoring terminal 3) and an embedded Web server. Since the Web servers 1A, 1B, 1C,... Have the same configuration, the configuration will be described below using the Web server 1A as an example.

  The Web server 1A includes an arithmetic processing unit 30, communication units 31 and 32, a shared data storage unit 33, and an operation information storage unit 34 as main components. The arithmetic processing unit 30 includes an operation information transmitting / receiving unit 36, a load estimating unit 37, a web page changing unit 38, and an abnormality information transmitting / receiving unit 39. Here, the monitoring control unit 35, the operation information transmission / reception unit 36, the load estimation unit 37, the web page changing unit 38, and the abnormality information transmission / reception unit 39 perform arithmetic processing by executing a program in which the arithmetic processing unit 30 is incorporated in advance. This is realized by the arithmetic function of the unit 30.

  The communication unit 31 communicates with terminals in its own area via the local network 4.

  The communication unit 32 communicates with the client terminal 6 and other Web servers 1B, 1C,.

  The shared data storage unit 33 stores static contents (images, HTML, scripts, CSS, etc.) that are common among the Web servers.

  The operation information storage unit 34 stores operation information including at least past load information of each of the Web servers 1A, 1B, 1C... And operation schedule information by the monitoring control unit 35 described later.

  The monitoring control unit 35 monitors or controls the subordinate terminals (the control terminal 2 and the monitoring terminal 3) via the local network 4.

  The operation information transmission / reception unit 36 transmits and receives operation information between Web servers via the communication network 5 in a predetermined time zone, for example, a time zone such as midnight or early morning when the load is lower than other time zones. The operation information of each Web server 1A, 1B, 1C... Includes past load information of each Web server 1A, 1B, 1C... And the operation schedule information of the day by the monitoring control unit 35 of each Web server 1A, 1B, 1C. (The control schedule of the control terminal 2 and the monitoring schedule of the monitoring terminal 3). As load information, for example, the load (client terminal 6 or other Web server) measured by the Web servers 1A, 1B, 1C,. And the load information measured by the Web servers 1A, 1B, 1C... On the same day of last week.

  When the communication unit 32 receives a transmission request for a Web page described in the Web description language from the client terminal 6, the load estimation unit 37 receives a transmission request when the transmission request is received based on the operation information stored in the operation information storage unit 34. Estimate the load on each Web server.

  When the communication unit 32 receives the transmission request from the client terminal 6, the web page changing unit 38 analyzes the requested web page and loads the link destination of the static content pasted in the web page. In order to rewrite to a lower Web server, a process of changing the Web page is performed.

  When the abnormal information transmitting / receiving unit 39 detects an abnormal state of a terminal (control terminal 2 or monitoring terminal 3) in its own area, the abnormal information transmitting / receiving unit 39 transmits abnormal information for notifying the abnormal state to the other Web servers 1B, 1C. The abnormal information from the Web servers 1B, 1C.

  Next, a load distribution method by the Web server system of this embodiment will be described with reference to FIGS.

  The arithmetic processing unit 30 of each of the Web servers 1A, 1B, 1C,... Stores past load information, for example, the previous day's load information and the result of measuring the same day's load information in a memory (not shown). When a predetermined time zone such as midnight or early morning comes every day, the operation information transfer unit 36 communicates with another Web server using the communication unit 32, and the past load information and the operation schedule information of the day. The operation information including at least is exchanged between Web servers (step S1 in FIG. 2). Then, in the arithmetic processing unit 30 of each Web server 1A, 1B, 1C,..., The operation information transferred by the operation information transfer unit 36 is stored in the operation information storage unit 34 (step S2).

  Thereafter, when the business hours of the tenant in the building using this system come, the monitoring control unit 35 of each Web server 1A, 1B, 1C... Controls the control terminal 2 according to a preset operation schedule. When monitoring information corresponding to the switch operation is input to the monitoring control unit 35 from the monitoring terminal 3 that monitors the operation input of the operation switch, the monitoring control unit 35 displays the control terminal 2 associated with the monitoring terminal 3. To control the operation of the load corresponding to the operation switch.

  Then, in a state where each Web server 1A, 1B, 1C is monitoring or controlling a terminal in each area, the client terminal 6 connected to the communication network 5 makes a desired static response to the Web server 1A, for example. When a transmission request for the HTML file (Web page) to which the link destination of the target content is attached (step S3), the communication unit 32 of the Web server 1A receives this transmission request and outputs it to the arithmetic processing unit 30.

  When receiving the transmission request from the client terminal 6, the arithmetic processing unit 30 of the Web server 1A causes the load estimation unit 37 to estimate the current load state of each Web server (step S4). Here, the load estimation unit 37 estimates the load of each Web server at the present time based on the operation information stored in the operation information storage unit 34, that is, the past load information of each Web server and the operation schedule information on that day. To do.

  When the load estimation by the load estimation unit 37 is completed, the web page changing unit 38 of the arithmetic processing unit 30 analyzes the requested HTML file and extracts the static content link attached to the HTML file. At the same time, the static content link destination is rewritten to a Web server with a lower load based on the load estimation result in step S4 (step S5). Thereafter, the Web page changing unit 38 returns the HTML file whose link destination has been rewritten from the communication unit 32 to the requesting client terminal 6 (step S6). Therefore, the requesting client terminal 6 receives the HTML file in which the link destination of the static content is rewritten, and requests the transmission of the static content with the link attached to the HTML file after receiving the HTML file. Then, a static content transmission request is sent to the Web server whose link destination has been changed, and the requested static content is transmitted from the Web server to the client terminal 6 (step S7).

  As described above, in the Web server system of the present embodiment, the operation information transfer unit 36 of each Web server 1A, 1B, 1C... Transfers the operation information of other Web servers at a predetermined time period, and operates. When the Web server (HTML file) transmission request is received from the client terminal 6 and stored in the information storage unit 34, the load estimation unit 37 receives each Web server 1A, 1B at the time of reception based on the stored operation information. , 1C... Is estimated. Therefore, even when there is no load balancer that measures the load status of each Web server in real time, it is possible to estimate the load of each Web server 1A, 1B, 1C. Then, the Web page changing unit 38 of each Web server 1A, 1B, 1C,... Rewrites the link destination in the Web page to a Web server with a lower load based on the load estimation result by the load estimating unit 37. Therefore, when the client terminal 6 requests transmission of static content to the link destination in the Web page, the transmission request is transmitted to the changed link destination Web server, and it is estimated that the load is low. Load can be distributed to Web servers. Also, in the Web server 1A that receives the HTML file transmission request from the client terminal 6, the load distribution is performed by rewriting the link destination attached to the HTML file returned to the client terminal 6 to a Web server having a lower load. Therefore, the number of communications during the request processing from the client terminal 6 can be reduced to prevent an increase in load.

  By the way, the monitoring control unit 35 of each Web server 1A, 1B, 1C,... Demands that suppresses the operation of the load so that the abnormal state of the terminal in its own area (for example, fire, power failure, or power consumption does not exceed the demand peak) When a control state or the like is detected, the abnormality information transmission / reception unit 39 transmits notification information for notifying the abnormality state to another Web server via the communication unit 32. Further, when an abnormal state occurs in another Web server, the abnormality information transmission / reception unit 39 receives the abnormality information transmitted from the other Web server via the communication unit 32. Thus, the arithmetic processing unit 30 of each of the Web servers 1A, 1B, 1C,... Can grasp the Web server that is sending the abnormal information, and the Web page changing unit 38 performs the HTML file processing in step S5. If the Web server that has notified the abnormality information is removed from the change target when changing the link destination in the Web server 1A, 1B, Since the load of 1C... Can be reduced, processing corresponding to the abnormal state (for example, processing for notifying the abnormal state) can be reliably performed.

  Further, the operation schedule information of each Web server 1A, 1B, 1C... May be changed during operation, and when the operation schedule information is changed in any Web server, the load on each Web server is accurately predicted. In order to do so, it is necessary to exchange the changed schedule information between Web servers. Therefore, when the operation schedule information is changed in any Web server (for example, Web server 1A), the operation information transfer unit 36 of the Web server 1A sends the changed operation schedule information from the communication unit 32 to another Web server. 1B, 1C,... And the changed operation schedule information is reflected on the other Web servers 1B, 1C,. Therefore, in each Web server 1A, 1B, 1C ..., even when the operation schedule information is changed in any of the Web servers 1A, 1B, 1C ..., the transmission request is received on the basis of the changed operation schedule information. Since the load of each Web server 1A, 1B, 1C... Can be estimated, the load can be predicted more accurately.

  Here, congestion information (for example, a control schedule is concentrated on the operation information transfer unit 36 of each Web server 1A, 1B, 1C,...) Indicating a time zone in which the load on each Web server is relatively large compared to other time zones. If the operation schedule information is changed in any one of the Web servers 1A, 1B, 1C, etc. during the congestion time, the operation information transfer unit 36 of the Web server before the change Only the part changed from the operation schedule information (difference information) may be transmitted to the other web servers 1B, 1C..., And only the difference information is exchanged between the web servers without increasing traffic. The change contents of the operation schedule information can be reflected on other Web servers.

  In this embodiment, the Web page changing unit 38 of each Web server 1A ... performs processing of rewriting the link destination in the Web page to a Web server with a lower load based on the estimation result of the load estimating unit 37. The processing of rewriting the link destination in the Web page may be performed on the client terminal 6 side.

  When rewriting the link destination on the client terminal 6 side, the Web page changing unit 38 replaces the link destination in the above-described step S6, and instead of rewriting the link destination, each Web server 1A, 1B, After the load information of 1C... And the processing instruction (function) for executing the process of rewriting the link destination of the static content based on the load information are written in the HTML file, the HTML file is returned to the client terminal 6. Then, when the browser software installed in the client terminal 6 completes reading the HTML file returned from the Web server, that is, immediately after analyzing the content of the HTML file, the processing instruction written in the HTML file is executed. By executing, the link destination of the static content in the HTML file is rewritten to a Web server with a lower load. Therefore, when the client terminal 6 requests transmission of static content to the link destination in the Web page, the transmission request is transmitted to the changed link destination Web server, and it is estimated that the load is low. Load can be distributed to Web servers. As described above, since the link rewriting process performed on the Web servers 1A, 1B, 1C... Is performed on the client terminal 6 side, the load on the Web servers 1A, 1B, 1C. Here, the web servers 1A, 1B, 1C,... Are configured by incorporating a web server function in the controller. Generally, an embedded web server has a lower CPU processing capacity than the client terminal 6, and also has a memory capacity to be mounted. Since it is small, it can be said that the load reduction effect on the Web server side is large.

  It should be noted that a wide variety of different embodiments can be configured without departing from the spirit and scope of the present invention, and the present invention is not limited to a specific embodiment.

1 is a system configuration diagram showing a schematic configuration of a Web server system of an embodiment. It is a flowchart explaining operation | movement same as the above. It is a system block diagram of a central monitoring system. It is explanatory drawing of the load distribution method using a load balancer. (A) is explanatory drawing of the proxy type load distribution method, (b) is explanatory drawing of the load distribution method by link rewriting.

Explanation of symbols

1A, 1B, 1C Web server 6 Client terminal 30 Arithmetic processing unit 31, 32 Communication unit 33 Shared data storage unit 34 Operation information storage unit 35 Monitoring control unit 36 Operation information transfer unit 37 Load estimation unit 38 Web page change unit 39 Abnormal information Transceiver

Claims (5)

In a web server system in which a plurality of web servers providing web services and client terminals are connected via a communication network,
Each Web server includes a monitoring control unit that monitors or controls subordinate terminals, a shared data storage unit that stores common static content among the Web servers, past load information and monitoring control of each Web server An operation information exchange unit that exchanges operation information including at least operation schedule information by a unit between Web servers in a predetermined time zone, an operation information storage unit that stores acquired operation information, and the static information described in the Web description language. A load estimation unit that estimates a load of each Web server based on the operation information when receiving a transmission request of a Web page to which a link destination of a target content is pasted from a client terminal, and an estimation of the load estimation unit Based on the result, the web page is changed in order to rewrite the link destination in the web page to a web server having a lower load. Web server system, characterized in that a Web page change unit.   The operation information sending / receiving unit has congestion time information indicating a time zone in which the load is relatively large compared to other time zones, and the operation schedule information is changed on any of the Web servers during the congestion time 2. The Web server system according to claim 1, wherein the changed difference information is exchanged between the Web servers.   The web page changing unit is configured to generate static content based on the load information of each web server estimated by the load estimating unit and the load information when browser software installed in a client terminal analyzes the web page. The Web server system according to claim 1, wherein a processing command for executing processing for changing the link destination of the client on the client terminal side is written in the Web page.   When the Web server detects an abnormal state of the terminal to be monitored or controlled, the Web server transmits abnormal information for notifying the abnormal state to another Web server and receives abnormal information from the other Web server. The web page changing unit, when changing the link destination in the Web page, excludes the Web server that has notified the abnormal state from the target of the change destination. The Web server system according to claim 1. A load balancing method for a Web server system in which a plurality of Web servers providing Web services and client terminals are connected via a communication network,
A step of exchanging operation information between Web servers in a predetermined time zone at least including operation information including past load information of each Web server and operation schedule information by the monitoring control unit;
A step in which a Web server stores operation information acquired from another Web server in an operation information storage unit;
When the Web server receives a transmission request for a Web page described in the Web description language and to which the link destination of the static content is pasted from the client terminal, it is received based on the operation information stored in the operation information storage unit. Estimating the load on each of the web servers;
A Web server comprising: a step of changing the Web page to rewrite a link destination in the Web page to a Web server having a lower load based on a result of estimating a load of each Web server. Load balancing method.

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