The data service 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:

1
2
3
4
5
6
<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 the data service on different machines:

1
2
3
4
5
6
7
8
<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 service. 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:

1
<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 service. 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.

Real-time store count

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

Changing the Topology

If you need to change the topology, including:

• Add or remove data service nodes
• Change the host name
• Change the port
• Change the real-time store count

Then you'll need to make configuration changes to the data-server-cluster parameter and restart both the data server and the application server by following these steps:

1. Stop the data service on all of the servers:
   • <APPIAN_HOME>/data-server/bin/stop.sh (.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. If adding nodes (e.g. when migrating from a single node to High Availability), copy the <APPIAN_HOME>/ae/data-server/data directory to the new servers.
4. Make the required topology change on all of the servers.
5. Start the data service on all of the servers in any order:
   • <APPIAN_HOME>/data-server/bin/start.sh (.bat on Windows)
6. Restart the application server on all servers:
   • To stop the server: <APPIAN_HOME>/tomcat/apache-tomcat/bin/stop-appserver.sh (.bat on Windows)
   • To start the server: <APPIAN_HOME>/tomcat/apache-tomcat/bin/start-appserver.sh (.bat on Windows)