Configuring the Data Server

The data server configuration is specified in data-server-cluster element in the appian-topology.xml file, located in both the <APPIAN_HOME>/ae/data-server/conf/ and <APPIAN_HOME>/ae/conf directories:

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<topology>
    ...
    <data-server-cluster>
        <data-server host="machine1.example.com" port="5400" rts-count="2"/>
    </data-server-cluster>
</topology>

For a high availability configuration, specify three instances of data server on different machines:

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<topology>
    ...
    <data-server-cluster>
        <data-server host="machine1.example.com" port="5400" rts-count="2"/>
        <data-server host="machine2.example.com" port="5400" rts-count="2"/>
        <data-server host="machine3.example.com" port="5400" rts-count="2"/>
    </data-server-cluster>
</topology>

The data-server-cluster configuration must be specified in appian-topology.xml. The appian-topology.xml file must be copied from <APPIAN_HOME>/conf/ into <APPIAN_HOME>/data-server/conf/ before starting the data server. Copies of the topology file in each location must always be in sync, irrespective of the configurations specified.

Node

A data-server node element must be present and must be structured similarly to the following:

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<data-server host="machine3.example.com" port="5400" rts-count="2"/>

If there is no data-server node element specified, the following error is printed in watchdog.log:

"ERROR com.appian.data.server.Watchdog - At least one data-server node must be specified"

Host

Set the host attribute in the data-server element to the name of the machine hosting the data server. If the host is not specified, the following error is printed in watchdog.log:

"ERROR com.appian.data.server.Watchdog - data-server host must be specified"

Port

The port attribute can be defined on both the data-server-cluster and the data-server elements. If defined on both, the data-server element takes precedence. If not supplied, the default port number is 5400.

In order for the data server to function properly, make sure that you open all of the required ports. See Port Usage for more information.

Real-time store count

The rts-count attribute determines the number of real-time stores in the data server. Multiple real-time stores provide horizontal read scalability. Appian supports running exactly 2 instances of the real-time store only. When configuring the attribute value, set it to rts-count="2".

Changing the Topology

When you want to add or remove data server nodes, change the host name, or change the port, you'll need to make configuration changes to the data-server-cluster parameter by taking the following steps:

  1. Stop the data server on all the servers by executing <APPIAN_HOME>/data-server/bin/stop.sh on Linux or <APPIAN_HOME>\data-server\bin\stop.bat on Windows.
  2. Delete the <APPIAN_HOME>/ae/data-server/node/election directory from all the servers. This directory contains runtime data that needs to be deleted when certain topology changes are made.
  3. Make the required topology change on all the servers.
  4. Start the data server on all the servers in any order by executing <APPIAN_HOME>/data-server/bin/start.sh on Linux or <APPIAN_HOME>\data-server\bin\start.bat on Windows.
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