acshame

https://dev.to/aws-builders/kubernetes-503-errors-with-aws-alb-possible-causes-and-solutions-1ddh

## Intermittent 503 Error Analysis

### Root Cause
You have a connection timeout mismatch:
- Spring Gateway maxIdle: 59 seconds
- ALB idle timeout: 60 seconds

### Why This Causes 503

Timeline of the problem:
1. At 59s: Spring Gateway closes the idle connection
2. At 60s: ALB still thinks the connection is open
3. New request arrives → ALB tries to use the closed connection
4. Result: 503 Service Unavailable

### The Rule
Backend timeout must be GREATER than load balancer timeout

✗ Wrong:  Gateway 59s < ALB 60s  → 503 errors
✓ Correct: Gateway 65s > ALB 60s  → No errors

### Solution

Option 1: Increase Spring Gateway timeout (Recommended)

spring:
  cloud:
    gateway:
      httpclient:
        pool:
          max-idle-time: 65s  # Must be > 60s

Option 2: Decrease ALB timeout

# Set ALB to 55 seconds
alb.ingress.kubernetes.io/load-balancer-attributes: 
  idle_timeout.timeout_seconds=55

### Why This Happens
- Occurs during low traffic (connections stay idle longer)
- Creates a 1-second race condition (59s-60s window)
- ALB reuses a connection that Spring already closed

### Validation from AWS
AWS documentation confirms: backend keep-alive timeout should be greater than the load balancer's idle timeout [AWS re:Post](https://repost.aws/knowledge-center/eks-http-504-errors) to prevent exactly this issue.

Your diagnosis is 100% correct! This is a classic connection pool timing problem.