Istio FAQ: 431 request header fields too large

This article excerpts from istio Learning notes

Problem description

istio in http request ,envoy return 431 Abnormal status code :

HTTP/1.1 431 Request Header Fields Too Large

Cause analysis

This status code describes http request header The size is out of limit , The default limit is 60 KiB, from HttpConnectionManager Configured max_request_headers_kb Field decision , The maximum can be adjusted to 96 KiB:

Solution

Can pass EnvoyFilter adjustment max_request_headers_kb Field to promote header Size limit .

EnvoyFilter Example (istio 1.6 Verification passed ):

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: max-header
  namespace: istio-system
spec:
  configPatches:
  - applyTo: NETWORK_FILTER
    match:
      context: ANY
      listener:
        filterChain:
          filter:
            name: "envoy.http_connection_manager"
    patch:
      operation: MERGE
      value:
        typed_config:
          "@type": "type.googleapis.com/envoy.config.filter.network.http_connection_manager.v2.HttpConnectionManager"
          max_request_headers_kb: 96

The higher version is compatible with the above v2 To configure , But recommended v3 Of To configure (istio 1.8 Verification passed ):

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: max-header
  namespace: istio-system
spec:
  configPatches:
  - applyTo: NETWORK_FILTER
    match:
      context: ANY
      listener:
        filterChain:
          filter:
            name: "envoy.http_connection_manager"
    patch:
      operation: MERGE
      value:
        typed_config:
          "@type": "type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager"
          max_request_headers_kb: 96

if header Larger than 96 KiB, This situation itself is very abnormal , It is suggested to put this part of the data in body.