why my wordpress site always timed out everyday

At first, I built a wordpress site on EC2 and after few days , website always shows timed out message. And then I move to Lightsail and it still shows same wrong msg, even I reset website but still not working. But I can login ssh and sftp but SQL site can't connect. My domain name is using route53 and I set a aws alarm, here is alarm msg shows: Alarm Details:

• Name: awsroute53-25103daa-41c8-4e4f-a07e-86f23770222f-Low-HealthCheckStatus
• Description:
• State Change: OK -> ALARM
• Reason for State Change: Threshold Crossed: 1 datapoint [0.0 (10/02/22 07:27:00)] was less than the threshold (1.0).
• Timestamp: Thursday 10 February, 2022 07:28:37 UTC
• AWS Account: xxxxxxxx0044
• Alarm Arn: arn:aws:cloudwatch:us-east-1:401785220044:alarm:example-com-awsroute53-25103daa-41c8-4e4f-a07e-86f23770222f-Low-HealthCheckStatus

How should I test connecting problem? Or where can find the solution?