HCX Manager UI is inaccessible showing a blank white page

Products

• VMware HCX

Issue/Introduction

• In VMware HCX, the Manager UI may become unresponsive and display a blank white page.
• Trying to login via 443 or vCenter plugin shows the same white page.
• While the web interface is inaccessible, the appliance may still respond to ICMP pings and SSH sessions.
• High CPU load averages observed via the top command
• /common/logs/zookeeper.log may report expiring sessions : 

  • 20##-##-## 13:##:##,7## [myid:] - INFO  [NIOWorkerThread-9:o.a.z.s.NIOServerCnxn@342] - Unable to read additional data from client, it probably closed the socket: address = /127.0.0.1:60612, session = 0x1000######c0000
    20##-##-## 13:##:##,7## [myid:] - INFO  [NIOWorkerThread-16:o.a.z.s.NIOServerCnxn@342] - Unable to read additional data from client, it probably closed the socket: address = /127.0.0.1:60614, session = 0x100000######001
    20##-##-## 13:##:##,7## [myid:] - INFO  [NIOWorkerThread-1:o.a.z.s.NIOServerCnxn@532] - Processing srvr command from /127.0.0.1:35202
    20##-##-## 13:##:##,7## [myid:] - INFO  [NIOWorkerThread-2:o.a.z.s.NIOServerCnxn@532] - Processing srvr command from /127.0.0.1:35204
    20##-##-## 13:##:##,7## [myid:] - INFO  [SessionTracker:o.a.z.s.ZooKeeperServer@730] - Expiring session 0x10000########4a, timeout of 4000ms exceeded

• /common/logs/httpd/error.log may report timeut expired events : 
  

  • [Thu ### ## ##:##:##.041785 2026] [proxy_http:error] [pid 5##4:tid 5683] (70007)The timeout specified has expired: [client ###.##.38.##:32888] AH01102: error reading status line from remote server 127.0.0.1:8443
    [Thu ### ## ##:##:##.041991 2026] [proxy_http:error] [pid 5##4:tid 5677] (70007)The timeout specified has expired: [client ###.##.###.##:64207] AH01102: error reading status line from remote server 127.0.0.1:8443
    [Thu ### ## ##:##:##.042457 2026] [proxy_http:error] [pid 5##4:tid 5675] (70007)The timeout specified has expired: [client ##.##.###.##:60900] AH01102: error reading status line from remote server 127.0.0.1:8443

Environment

VMware HCX

Cause

• This issue is caused by resource exhaustion OR disk I/O latency.
• When the system cannot process requests within the defined timeout periods, internal services (Zookeeper and Java-based web services) become desynchronized, leading to an unresponsive UI.

Resolution

• Restart the Appliance: Power cycle the HCX Manager appliance from the vSphere Client to clear the hung state and restore UI access.
• Ensure the appliance is residing on a storage backing that can handle high I/O bursts. Avoid placing the Manager on heavily congested or slow mechanical storage tiers.
• Increase the CPU reservation for the HCX Manager appliance if high-churn operations are expected in the environment.

Additional Information

Refer to article 373010 for scalability guide.