Customer reported issue with EX4400 as they are observing yellow alarm light, but there were no logs/alarms evident on the support information.
Each EX4400 switch has four chassis status LEDs (labeled SYS, ALM, MST, and CLD) on the right-hand side of the front panel.
If LED label ALM, is in Red color, then it states that there is a major hardware fault, such as a temperature alarm or a power failure alarm, and the switch is halted. A major alarm indicates a critical error condition that requires immediate attention. Below command output can be verified to isolate the ALM state:
root@switch> show chassis alarmroot@switch> show chassis led root@switch> show chassis environment
If there is no LED light/unlit, indicates that there is no alarm or the switch is been halted.
If it is in AMBER, then it indicates that there is a minor alarm, such as a software or a hardware error. Power off the switch and then power it on. Monitor the switch to see whether it is working properly. A minor alarm indicates a noncritical condition that requires monitoring or maintenance. A minor alarm that is left unchecked might cause interruption in service or performance degradation.
Check the LED status of ALM and take necessary action as per the above options.
https://www.juniper.net/documentation/us/en/hardware/ex4400/topics/topic-map/ex4400-chassis.html