Version 25.3.9469

• Overview
• Configuring Arc for Clustering
  • Licensing
  • Application Database
    • .NET Edition
    • Embedded Java Server
    • External Java Server
  • Application Data Directory
    • .NET Edition
    • Embedded Java Server
    • External Java Server
  • Locking and Concurrency
  • Configuring Reverse Proxies
    • Cross-Platform Edition
    • .NET Edition
    • Example: Setting a Reverse Proxy Using an nginx Proxy

Clustering allows multiple CData Arc installations to work together, processing the same data with the same configuration. Workloads can be distributed horizontally across clustered Arc installations to improve scalability and ensure availability.

Overview

To take advantage of the high-availability and failover features supported in Arc, the application should be installed on multiple systems in the same server farm (the same cluster). A load balancer then distributes incoming traffic across the multiple systems hosting Arc instances.

When configured for clustering, each Arc installation in the server farm uses the same application configuration, processes data to and from the same locations on disk, and logs transactions in the same database tables.

As a result, multiple instances of the application behave like a single instance, and any particular instance can go down without jeopardizing the performance of the cluster.

Configuring Arc for Clustering

After Arc has been installed on each node in the cluster, each installation should be configured to use the same Application Database and Application Data Directory.

Licensing

You must apply a unique license key to each node in the cluster. Go to the licensing page for each node and apply one of your keys. The application creates a license file in the shared directory of the cluster. The license file name includes the machine name of both nodes in the shared directory.

Application Database

Arc uses a database to log transaction history and any errors that occur in the application. Each instance of Arc should be configured to use the same application database to ensure that all files processed end up consolidated in the database.

.NET Edition

To configure the application database in the .NET edition, the AppDb environment variable must be set to include the appropriate connection string and provider. To accomplish this, modify the Web.Config file in the www folder of the installation directory. In this file is a commented-out XML element called connectionStrings, for example:

<!-- connectionStrings>
 <add 
  name="AppDb" 
  connectionString="server=SQLSERVER_LOCATION;database=DATABASE_NAME;uid=USER_ID;password=PASSWORD;" 
  providerName="System.Data.SqlClient"
 />
</connectionStrings -->

Un-comment this connectionStrings element and set the connectionString and providerName attributes to the appropriate connection parameters for the desired database. If Arc can successfully establish a connection with this connection string, it uses this database as the application database.

Embedded Java Server

When using the Cross-Platform edition with the embedded Jetty server, the application database is configured in the arc.xml file found in the “webapp” folder of the installation directory. In this server configuration file, the APP_DB environment variable must be set to a JDBC connection string containing the appropriate connection parameters for the desired database. For example:

<Call name="setInitParameter">
 <Arg>APP_DB</Arg>
 <Arg>jdbc:cdata:mysql:Server=MySQLServer;Port=3306;Database=mysql;User=user;Password=password</Arg>
</Call>

If Arc can successfully establish a connection with the APP_DB connection string, it uses that database as the application database.

External Java Server

When using the Cross-Platform edition with an external Java servlet (any server other than the Jetty server that is included with the application), the details of configuring the application database depend upon the specific servlet used. Using the syntax appropriate for the specific servlet, one of the following approaches should be used when configuring the server:

• Define a JNDI datasource to include the connection properties for the target database.
• Set the APP_DB environment variable to a JDBC connection string.

If Arc can use the JDNI datasource or APP_DB connection string to connect to a database, it uses that database as the application database.

Application Data Directory

Arc stores all configuration data and application data in a folder on disk called the data directory. When clustering, each instance of Arc should be configured to use the same data directory. This ensures that all instances are processing the same files and using the same configuration.

.NET Edition

To configure the application data directory in the .NET edition, the AppDirectory environment variable must be set to the path where the directory should be created. To accomplish this, modify the Web.Config file in the ‘www’ folder of the installation directory. In this file is a commented-out XML element called AppDirectory, and below this an element called appSettings where a custom data directory location can be specified:

<!-- appSettings>
 <add key="AppDirectory" value="C:\\directory\\subdirectory\\subdirectory\\" />
</appSettings -->

Un-comment this appSettings element and set the AppDirectory key value to the appropriate path on disk for the data directory. If Arc can find the path, and has the appropriate permissions to read and write at the given path, it creates the data folder in the specified directory.

Embedded Java Server

When using the Cross-Platform edition with the embedded Jetty server, the application database is configured in the arc.xml file found in the “webapp” folder of the installation directory. In this server configuration file, the AppDirectory environment variable must be set to the path to the desired directory. The following example demonstrates what this might look like when setting the data directory to a shared folder on a mounted drive:

<Call name="setInitParameter">
 <Arg>AppDirectory</Arg>
 <Arg>/mnt/shared/arc</Arg>
</Call>

If Arc can find the path, and has the appropriate permissions to read and write at the given path, it creates the data folder in the specified directory.

External Java Server

When using the Cross-Platform edition with an external Java servlet (any server other than the Jetty server that is included with the application), the details of configuring the application data directory depend upon the specific servlet used. Using the syntax appropriate for the specific servlet, the AppDirectory environment variable must be set to the path to the desired directory.

If Arc can find the AppDirectory path, and has the appropriate permissions to read and write at the given path, it creates the data folder in the specified directory.

Locking and Concurrency

Arc uses locks to ensure that multiple instances do not interfere with each other or process the same file twice. In a clustered environment, efficient locking is critical to maintain throughput and prevent collisions. Thus it is strongly recommended not to cluster Arc instances across multiple server farms, such that file system latency might come into play.

Setting a shared Application Directory for each instance of Arc is sufficient to ensure that the file locks are respected by each instance.

Configuring Reverse Proxies

A reverse proxy is a server that sits between clients and backend servers, intercepting incoming traffic and forwarding it to the appropriate destination. When configured properly, reverse proxies can preserve the real client IP address through header forwarding while protecting your backend infrastructure from direct exposure. This architecture provides benefits such as load balancing, improved security, caching, and SSL termination.

When a reverse proxy forwards client information through headers like X-Forwarded-For, it is critical to restrict which proxies are trusted. If you don’t explicitly trust only your known proxy IP addresses, malicious users can fabricate these headers to spoof their origin, potentially bypassing security controls or logging mechanisms.

Cross-Platform Edition

To configure reverse proxies in the Cross-Platform edition, set the proxyMode setting in the arc.properties file to true, as shown in the following string: cdata.http.proxyMode=true.

When proxyMode=true, the embedded Jetty server uses ForwardedRequestCustomizer to extract and apply the real client IP from forwarded headers.

If you are using an external Java servlet container, configure request rewriting at the servlet level to handle forwarded headers appropriately.

.NET Edition

To configure reverse proxies in the .NET edition, you must provide a comma-separated list of header names that the app should use to determine the client IP address in the HTTP Forwarded Header field on the Proxy Settings portion of the Security page.

Example: Setting a Reverse Proxy Using an nginx Proxy

It is the proxy’s responsibility to ensure clients cannot spoof the header being used for the forwarded IP address. This example illustrates a proxy setting which includes reverse proxy settings.

location /arc/ {
  proxy_pass http://localhost:8080/;
  proxy_set_header Host              $host;
  proxy_set_header Referer           $http_referer;
  proxy_set_header X-Forwarded-For   $proxy_add_x_forwarded_for;
  proxy_set_header X-Forwarded-Proto $scheme;
  proxy_set_header X-Forwarded-Port  $server_port;
  proxy_set_header X-NginX-Proxy     true;
  proxy_redirect http://localhost:8008/ http://$host:8008/arc/;
}
  <!-- Declare all trusted IP or CIDR -->
  set_real_ip_from 192.168.1.100;
  set_real_ip_from 10.0.0.0/8;

  <!-- Define the request header field whose value will be used to replace the client address -->
  <!-- It affects the Nginx interval variable "$remote_addr" -->
  real_ip_header X-Forwarded-For;

  <!-- Enable recursive resolution to skip all trusted proxy IPs from X-Forwarded-For -->
  real_ip_recursive on
  
  <!-- Optionally, set the real client IP to a new header -->
  Jetty_Forwarded-For: $remote_addr

This configuration prevents header spoofing by explicitly trusting only the specified proxy IPs (192.168.1.100 and 10.0.0.0/8). If a malicious user fabricates an X-Forwarded-For header, nginx ignores it and uses the IP closest to the client that came through the trusted proxy.