DPE Business Layer failed to start on APE due to unresolved Main Polling Engine (MPE) FQDN

3/9/2026 4:02 PM

3/31/2026 2:29 PM

Environment

• SolarWinds Platform: 2025.4 (Core 2025.4.x)

• Modules: NPM, NCM, SAM (others may be present)

• Role: Additional Polling Engine (APE)

• OS: Windows Server (APE and MPE)

• Example hostnames:

  • MPE: <MPE_FQD (FQDN), <MPE_ShortName> (short name)

  • APE: <APE_Hostname>

Symptoms

Web console events

In Alerts & Activity → Events with Event Type = BL Plugin Failed to Start, the following messages appear repeatedly for the APE:

• Plugin "DPE Business Layer" failed to start on [<APE_Hostname>]. Please restart the Module Engine service on [<APE_Hostname>].

These events continue even after:

• Restarting Orion Module Engine on the APE

• Restarting all SolarWinds services on MPE and APE

• Rebooting the servers

DPE.BusinessLayer log on APE

On the APE, the log file:

• C:\ProgramData\SolarWinds\Logs\Orion\DPE\DPE.BusinessLayer.log

contains errors similar to:

2026-02-06 12:36:13,164 [11] ERROR ApiProxy<IDataSourceService, ServiceDirectoryQueryInternal> - All #15 retries calling an API channel from a pool 'RootPool' failed due to a transient error detected.
2026-02-06 12:36:13,308 [11] ERROR SolarWinds.Orion.Common.SWEventLogging - Unhandled Exception caught in Core Service Engine startup. Exception of type 'SolarWinds.ApiProxyFactory.TransientApiProxyException' was thrown.
2026-02-06 12:36:13,309 [11] FATAL SolarWinds.Orion.DataProcessingEngine.BusinessLayer.DpeBusinessLayerPlugin - Unhandled Exception caught in plugin startup.SolarWinds.ApiProxyFactory.TransientApiProxyException: Exception of type 'SolarWinds.ApiProxyFactory.TransientApiProxyException' was thrown.
 ---> System.ServiceModel.EndpointNotFoundException: No DNS entries exist for host <MPE_FQDN>.
 ---> System.Net.Sockets.SocketException: No such host is known
   at System.Net.Dns.GetAddrInfo(String name)
   ...
   at SolarWinds.Orion.DataProcessingEngine.BusinessLayer.DpeBusinessLayerPlugin.Start()

Key indicators:

• EndpointNotFoundException for the MPE FQDN

• No DNS entries exist for host <MPE_FQDN>

• SocketException: No such host is known

Network Performance Monitor

The DPE Business Layer on the APE connects to the main polling engine using the FQDN registered in the SolarWinds Service Directory (for example, via a URI like net.tcp://<MPE_FQDN>:17777/orion/dpe/businesslayer).

If the APE cannot resolve that exact FQDN (e.g., <MPE_FQDN>) to an IP address:

• DNS lookups fail.

• The DPE plugin cannot open a net.tcp channel to the MPE.

• The plugin throws TransientApiProxyException / EndpointNotFoundException and fails to start.

• The SolarWinds web console raises “DPE Business Layer failed to start” events on the APE.

Licensing or maintenance for the APE may also need to be valid, but in this scenario the remaining problem after fixing licensing is name resolution of the MPE FQDN from the APE.

Step 1 – Confirm DNS failure from the APE

On the APE (e.g., <APE_Hostname>):

1. Open Command Prompt or PowerShell.

2. Test name resolution of the MPE FQDN shown in the log <MPE_FQDN>

   nslookup <MPE_FQDN>
   ping <MPE_FQDN>
   

3. If these commands fail (host not found), DNS is not resolving the MPE FQDN from the APE.

Optionally, also verify connectivity to the DPE port (after fixing DNS):

Test-NetConnection <MPE_FQDN> -Port 17777

Step 2 – Add or fix DNS / hosts entry for the MPE FQDN

It is not recommended to modify the hosts file because manual changes are needed. This can introduce operational risk when IP addresses are changed because and will cause the application to stop working.  The recommendation is to use proper domain name resolution (DNS) through the existing DNS servers.

There are two options; use one of them:

Option A – Fix DNS (recommended long‑term)

• Create or correct the A record for <MPE_FQDN> in the internal DNS zone.

• Point it to the IP address of the MPE server (<MPE_ShortName>).

• Wait for DNS propagation.

• Re-test from the APE:

  nslookup <MPE_FQDN>
  ping <MPE_FQDN>
  

Option B – Add hosts file entry on the APE (quick fix)

If DNS cannot be changed immediately, add a static hosts file entry on the APE.

1. On <APE_Hostname>, open Notepad as Administrator.

2. Edit:

   • C:\Windows\System32\drivers\etc\hosts

3. Add a line using the MPE IP, FQDN, and optional short name, for example:

   <MPE_IP>  <MPE_FQDN>  <MPE_ShortName>
   

   Replace <MPE_IP> with the actual IPv4 address of the main polling engine.

4. Save the file.

5. Validate that the FQDN now resolves from the APE:

   nslookup <MPE_FQDN>
   ping <MPE_FQDN>

Step 3 – Restart SolarWinds services on the APE

After DNS/hosts is corrected:

1. On <APE_Hostname>, open Services.msc.

2. Restart:

   • SolarWinds Orion Module Engine

   • Optionally, all SolarWinds services on the APE.

3. Monitor the log:

   • C:\ProgramData\SolarWinds\Logs\Orion\DPE\DPE.BusinessLayer.log

   Confirm that:

   • No new EndpointNotFoundException: No DNS entries exist for host <MPE_FQDN> errors are logged.

   • Plugin startup completes without FATAL errors.

4. In the web console:

   • Go to Alerts & Activity → Events.

   • Filter on Event Type = BL Plugin Failed to Start.

   • Verify that no new “Plugin DPE Business Layer failed to start on [<APE_Hostname>]” events are generated after the restart.

   • Existing historical events can be cleared if desired.