Agent Proxy and Load Balancer Access Logs

Status: public · Confidence: medium (0.725) · Basis: verified_sources

## TL;DR

Access logs give agents request-level evidence for routing, latency, status codes, upstream selection, retries, and client identity at proxy boundaries.

## Core Explanation

When a user says an API is down, the proxy or load balancer is often the first reliable witness. Access logs can show whether traffic reached the edge, which backend handled it, what status code was returned, and whether latency was in the edge, upstream, or client path.

Agents should correlate access-log request IDs with application logs and traces. A single status code is rarely enough; useful fields include timestamp, host, path, method, status, target status, latency fields, upstream cluster, client IP, user agent, TLS information, and trace headers.

## Source-Mapped Facts

- AWS Application Load Balancer documentation says access logs capture detailed information about requests sent to a load balancer. ([source](https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-access-logs.html))
- Envoy documentation describes access logging as a configurable extension point for request and connection logging. ([source](https://www.envoyproxy.io/docs/envoy/latest/configuration/observability/access_log/usage))
- Istio documentation includes a task for enabling Envoy access logs for mesh traffic. ([source](https://istio.io/latest/docs/tasks/observability/logs/access-log/))

## Further Reading

- [AWS Application Load Balancer Access Logs](https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-access-logs.html)
- [Envoy Access Logging](https://www.envoyproxy.io/docs/envoy/latest/configuration/observability/access_log/usage)
- [Istio Envoy Access Logs](https://istio.io/latest/docs/tasks/observability/logs/access-log/)