Load Balancer 504 gateway timeout
I'm getting a lot of 504 gateway timeout when sending requests to my load balancer, especially when
The LB is hit with about 30 request/second, well under the 200 request/second mentionned here.
This doesn't seem to be correctly shown as a 5xx error code in the graphs of the load balancer, as the number of 5xx shown is inferior to the number I generate just by trying the endpoint manually.
When the request does get through, response time is always under 150ms.
I'm seeing 0 in the Queue metric for the droplets, and I have about 20 concurrent connections according to the LB.
Behind the LB is 3
2vCPU 2GB droplets running nginx as a reverse proxy to NodeJS (pm2 clusters with 1 instance per vCPU, so 6 instances of the application in total).
My questions are :
1 - What steps would you recommend I follow to isolate the cause of the 504 errors
2 - Why does the Queue metric never move from 0 even as I have tons of timeouts
I remain available for any clarification deemed necessary
Thanks in advance