Main Poller and Scalability Engines are Down After Upgrade to SolarWinds Platform 2026.1 due to gRPC Error Calling Feature Service on Port 17734

In the SolarWinds Observability Self-Hosted Platform, a new port, 17734, has been introduced for a gRPC feature service, which will run on the Main Polling Engine only.  If this port is blocked by firewalls, security groups, or network ACLs between SolarWinds servers, the platform services on Scalability Engines will fail to initialize properly, causing additional web site and polling engines to go down.

Symptoms:

Affected users may experience one or more of the following:

• Runtime error occurs when accessing the site, including through AWS
• Polling engines fail to communicate with the Primary Polling Engine
• Orion Module Engine service fails shortly after being manually started 

From the BusinessLayerHost.Log on the Scalability Engine:

2025-12-24 15:24:13,855 [8] ERROR SolarWinds.Orion.Feature.Client.Service.GrpcFeatureProviderAdapter - gRPC error calling Feature Service on port 17734: Error starting gRPC call. HttpRequestException: An error occurred while sending the request. WebException: Unable to connect to the remote server SocketException: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond MainPollerIP:17734

The Primary Website/Polling Engine may continue to function. 

The issue occurs when one the following conditions is true:

• Port 17734 is not open between SolarWinds servers (Primary Polling Engine, Additional Polling Engines, and Additional Web Servers).
• Main Polling Engine is not properly listening on port 17734

To resolve the problem, run the following netstat command on the Main Polling Engine to confirm port 17734 is listening

Resolution 1:

Step 1: Verify the Feature Service is running and listening on port 17734

• From an elevated PowerShell / CMD on the main polling engine:

netstat -ano | findstr :17734

• The output should be the following:

TCP    [::1]:XXXX            [::1]:17734            LISTENING        17488

• Confirm that port 17734 is in a LISTENING state.

2. Ensure loopback traffic is not intercepted or redirected

• Review configuration for any local web proxies, endpoint security agents, or traffic-filtering software installed on the SolarWinds server.
  • A proxy on the system account could redirect traffic to a different endpoint. Check these registries:
    • Computer\HKEY_USERS\S-1-5-18\Software\Microsoft\Windows\CurrentVersion\Internet Settings
    • Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings
    • Computer\HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
  • In case the above registry does not show any configured proxy settings, you can run this command to validate if a third-party proxy is running in PowerShell:
    • bitsadmin /util /getieproxy localsystem
    • 
• Exclude or bypass:
  • Traffic to localhost:17734
  • Traffic to[::1]:17734
  • Run this command in PowerShell:
    • bitsadmin /util /setieproxy localsystem NO_PROXY

Step 3: Open TCP port 17734 between the Primary Polling Engines and Scalability Engines (Additional Website and Additional Polling Engine).

• Ensure the port is allowed in:

  • Host-based firewalls (Windows Firewall)

  • Network firewalls

  • Security Groups and Network ACLs (if applicable)

• After opening/allowing the port, verify that:

  • Additional Web Console loads successfully

  • Additional Polling Engines show as Up

  • No new gRPC or port 17734 errors appear in BusinessLayerHost.log

Resolution 2: If the issue is for APE/AWS only

1. Verify that TCP port **17734** is open. If the port is open, run a Wireshark capture on the affected APE/AWS server.

2. Apply the following Wireshark filter:
   `ip.addr == xx.xx.xx.xx && tcp.port == 17734`
   (Replace `xx.xx.xx.xx` with the IP address of the affected server.)

3. The Wireshark capture above shows that port **17734** is open, but the session is being reset immediately after the connection is established.

4. In my case 02156098 , the customer confirmed that their security team observed that the **SSL App-ID** was not allowed along with port **17734**. After permitting the SSL App-ID, the issue was resolved.