“Unable to send command over Netty channel / command cannot be written into Redis. #6945

Our project has been frequently encountering this error:

“Unable to send command over Netty channel / command cannot be written into Redis.”

As a result, Redis commands fail before they are even sent, because the Netty channel cannot write data.

This is a relatively small Spring Boot project that uses WebSocket and Redis.

In our WebSocket implementation, when a client connection is established, Spring calls
afterConnectionClosed(...).

Inside afterConnectionEstablished, we currently perform some logic to record the user’s online duration, which involves Redis operations.

Recently, we started seeing errors related to Redis commands not being written into the Netty channel, and at the same time, the number of open handles / connections keeps increasing continuously.

This suggests that WebSocket lifecycle callbacks may be performing blocking Redis operations, which could be exhausting the WebSocket or Netty threads and eventually preventing Redis commands from being written to the channel.