Web Platform Configuration Strategies

Network Services

4.3.2 Web Platform Configuration Strategies

A Web site can be supported with as few as one platform or as many as six or more platforms, depending on site capacity and availability requirements. ArcGIS Server platform configuration strategy can adapt to the required system reliability, availability, and security needs. This section will address the Web software component configuration strategies. Web security requirements will be addressed in more detail in section 5.

ArcGIS Server performance metrics will be included later in sections 7 and 8 to address system performance and capacity planning.

The Web system architecture design alternatives are grouped as single-tier, two-tier, and three-tier

configurations. Simple configurations are easier to maintain and support. More complex configurations satisfy higher-capacity and system availability requirements. Production operations are normally supported with high availability configurations (configurations that will continue providing services following any single platform failure).

ArcGIS Server is designed to support a scalable Web architecture. Optimum platform environments are configured using standard commodity server platform technology. ArcGIS Server is licensed based on the number of platform processor core supporting the primary ArcGIS Server software components. Following are recommended platform configuration strategies for supporting standard GIS Web services.

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4.3.2.1 Single-Tier Platform Configuration

Figure 4-10 provides an overview of single-tier platform configurations. Single-tier configurations provide one or two platforms capable of supporting all Web service components. Most initial customer deployments with a small database can be supported by a single-tier architecture.

Figure 4-10

Single-Tier Platform Configurations

Standard Configuration: A complete Web site can be supported on a single hardware platform. This configuration is appropriate for Web service development and testing, sites with a limited number of service requests, and initial prototype deployments. A special single chip workgroup server license bundled with a Microsoft SQL Server database is available for customer sites that can be supported by a single platform configuration.

High-Availability Configuration: Most GIS server production operations require redundant server solutions, configured so the site remains operational in the event of a single platform failure. This configuration will continue to support production operations during single platform maintenance and upgrade and while configuring and publishing new services. This configuration includes (1) network load balancing to route the traffic to each of the servers during normal operations and only to the active server if one of the servers fails, (2) service manager load balancing to distribute spatial services processing load between the two platforms to avoid having requests back up on one server when extra processing resources are available on the other server (separate SOC containers are required on each platform to support this configuration), and (3) duplicated data servers that require a complete copy of the data.

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4.3.2.2 Two-Tier Platform Configuration

A two-tier architecture provides an optimum solution for sites supported with a separate database server. The two-tier high-availability option may become the most popular and practical configuration supporting most ArcGIS Server deployments.

The two-tier architecture in figure 4-11 includes GIS server and data server platforms. The Web server and GIS server components are located on the GIS server platform, and the data server is located on a separate data server platform. This is a popular configuration for sites with large volumes of data resources or existing data servers. A single copy of the data can support multiple server components in conjunction with other enterprise GIS data clients.

Figure 4-11

Two-Tier Platform Configurations (Separate Data Servers)

Standard Configuration: The standard configuration includes one GIS Web server platform with a separate single data server platform. The Web server is installed on the GIS Web server platform.

High-Availability Configuration: High-availability operations require redundant server solutions, configured so the site remains operational in the event of any single platform failure. This

configuration includes (1) network load balancing to route the traffic to each of the GIS Web servers during normal operations and only to the active GIS Web server if one of the servers fails, (2) SOM load balancing to distribute SOC processing load between the two GIS Web server platforms to avoid having requests back up on one server when extra processing resources are available on the other server (two SOC container groups are required on each GIS Web server platform to support this configuration), and (3) two data servers that are clustered and connected to a common storage array data source. The primary data server supports query services during normal operations, and the secondary data server takes over query services when the primary server fails. Data server clustering is not required if availability requirements are satisfied with a single data server.

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4.3.2.3 Three-Tier Platform Configuration

Three-tier configurations include Web server, map server/container machine, and data server tiers. Two configuration options are provided, based on the location of the ArcGIS Server SOM.

Figure 4-12 shows a three-tier configuration with the service manager located on the Web server tier. This configuration provides the simplest three-tier architecture (network load balancing handles Web tier failover), and would likely be the most popular solution. The three-tier configuration provides a scalable architecture, where the middle tier can support two or more platforms as required to support capacity requirements.

Figure 4-12

Three-Tier Platform Configuration—SOM on Web Tier

Standard Configuration: The standard configuration includes a single Web server with a separate container machine layer and a separate data server. The container machine layer can be a single platform or can be expanded to support several platforms, depending on the required site capacity.

SOM load balancing is provided by the GIS Web server service manager.

High-Availability Configuration: High-availability operations require redundant server solutions, configured so the site remains operational in the event of any single platform failure. This

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Figure 4-13 shows a three-tier configuration with the SOM located on the container machine tier. The Web server and SOM connectors are located on the Web server platform, and the SOM and SOC components are located on the container machine platforms. This could be a preferred configuration when supporting Java applications on Linux-based Web servers. In this configuration, all the COM-based software is located on the container machine tier. The failover scenarios are more complicated. If the SOM1 software fails, WAS1 will send maps to SOM2. SOM2 will return results to the parent WAS2 output file. Client will return to WAS1 to get results and will need a virtual disk mount to receive the result from the SOM2 output directory. It will still be necessary to configure SOM load balancing for optimum capacity during peak loads.

Figure 4-13

Three-Tier Platform Configuration—SOM on SOC Tier

Standard Configuration: The standard configuration includes a single Web server with a separate container machine layer. The container machine layer can be a single platform or can be expanded to support several platforms, depending on the required site capacity. Web application traffic balancing is supported by the GIS Web server SOM connectors. The ArcGIS Server implementation can be configured in a failover mode (SOM2 would be activated only if SOM1 fails). SOM load balancing is provided by the server manager components (preferably no more than two SOM components on the container machine tier). All of the container machines can host SOM1 and SOM1 instances, so both SOM1 and SOM2 will deploy dedicated SOC instances on each host platform. Separate data server is provided as a common data source. Administration of this architecture can become increasingly complex as additional container machines are deployed - most of this complexity is managed by the SOM dispatch software.

High-Availability Operations: High-availability operations require redundant server solutions, configured so the site remains operational in the event of any single platform failure. This

configuration includes (1) network load balancing to route the traffic to each of the GIS Web servers during normal operations and only to the active GIS Web server if one of the servers fails, (2) Web application traffic load balancing to distributed inbound load between the two SOM located on the container machine tier. (3) SOM load balancing to distribute SOC processing load between the

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resources are available on the other server (dedicated SOC containers are required on each container machine platform to support this configuration, with each SOC assigned to a parent SOM), and (4) data server configuration supporting enterprise requirements. Administration of this architecture becomes increasingly complex as additional map servers/container machines are deployed - most of this complexity is managed by the SOM dispatch software.

4.3.2.4 Three-Tier Service-Oriented Platform Configuration

ArcGIS Server Web Applications can be developed and deployed supported entirely by remote Web data services. It is also possible to provide these HTTP SOAP based services from a separate local ArcGIS Server Web site. Figure 4-14 provides an example of a ArcGIS Server Web configuration that supports an enterprise services architecture configured across a firewall.

Figure 4-14

Three-Tier Platform Configuration—Web Services Architecture

The internal GIS Web Servers are configured as identified in the earlier configurations. Web data services can be published by the internal GIS Web Servers supporting enterprise applications deployed on a separate Web application tier. Web services can be passed through the firewall using standard HTTP service protocols.

Many of the more powerful ArcGIS Server applications benefit from a more tightly coupled DCOM

communications. Each application is directly coupled to an assigned SOC to support each transaction. Results from these applications can be provided as services to more loosely coupled enterprise applications supported in

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Use of the ArcGIS 9.3.1+ optimized map document (MSD) or preprocessed cached data layers available with ArcGIS Server can improve user performance beyond what we saw with ArcIMS technology and reduce network traffic requirements. Careful attention to user requirements and proper deployment of the technology can make a difference.

In document System Design Strategies 26th Edition (Page 59-65)