# Istio Upstream Connection Overflow

## Backgroun

I found some failed request 503 error for the microservice deployment in Openshift 4.5 with Service Mesh v1. The error shown is upstream connect error or disconnect/reset before headers. reset reason: overflow.

## Problem

I found the solution during the search and refer to the documentation. It is because Service Mesh v1 is using (Istio 1.3)[https://istio.io/v1.3/docs/reference/config/networking/v1alpha3/destination-rule/#ConnectionPoolSettings-HTTPSettings]. And the Connection poll is set to 1024 for http1MaxPendingRequests, http2MaxRequests, etc. It is different from version 1.8 where it is default to 2^32-1. Therefore, it is required to set it differently.

## Solution

This is not really a good solution I believe. and it require sometime to investigate, but you can increase those settings with destination rules.

apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
name: sample-destinationrule
spec:
host: sample
trafficPolicy: