如何在Istio中设置含动态UUID或复用已有头部值的自定义请求头部？

一、复用已有请求头的值 #

Istio的VirtualService不支持直接引用其他请求头变量来拼接新头部，需要通过EnvoyFilter配置Envoy的Lua脚本实现类似Nginx的变量拼接逻辑。

比如要实现proxy_set_header x-custom-header $connection:$connection_requests的效果，可以用以下EnvoyFilter：

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: add-custom-header
  namespace: istio-system
spec:
  workloadSelector:
    labels:
      istio: ingressgateway # 针对网关配置，若要给边车生效则修改为对应工作负载标签
  configPatches:
    - applyTo: HTTP_FILTER
      match:
        context: GATEWAY # 可选值：GATEWAY/SIDECAR_INBOUND/SIDECAR_OUTBOUND
        listener:
          filterChain:
            filter:
              name: "envoy.filters.network.http_connection_manager"
              subFilter:
                name: "envoy.filters.http.router"
      patch:
        operation: INSERT_BEFORE
        value:
          name: envoy.filters.http.lua
          typed_config:
            "@type": "type.googleapis.com/envoy.extensions.filters.http.lua.v3.Lua"
            inline_code: |
              function envoy_on_request(request_handle)
                -- 获取连接ID和该连接的请求计数
                local connection_id = request_handle:streamInfo():downstreamConnectionId()
                local conn_request_count = request_handle:streamInfo():downstreamConnectionRequestCount()
                -- 拼接后添加自定义请求头
                request_handle:headers():add("x-custom-header", connection_id .. ":" .. conn_request_count)
              end

二、动态生成UUID作为请求头值 #

VirtualService不支持动态生成UUID，必须通过EnvoyFilter实现，有两种便捷方式：

方式1：Lua脚本生成UUID #

通过Lua内置函数生成UUID并注入请求头：

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: add-uuid-header
  namespace: istio-system
spec:
  workloadSelector:
    labels:
      istio: ingressgateway
  configPatches:
    - applyTo: HTTP_FILTER
      match:
        context: GATEWAY
        listener:
          filterChain:
            filter:
              name: "envoy.filters.network.http_connection_manager"
              subFilter:
                name: "envoy.filters.http.router"
      patch:
        operation: INSERT_BEFORE
        value:
          name: envoy.filters.http.lua
          typed_config:
            "@type": "type.googleapis.com/envoy.extensions.filters.http.lua.v3.Lua"
            inline_code: |
              -- 生成UUIDv4的Lua函数
              function generate_uuid()
                local template = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'
                return string.gsub(template, '[xy]', function(c)
                  local v = (c == 'x') and math.random(0, 0xf) or math.random(8, 0xb)
                  return string.format('%x', v)
                end)
              end

              function envoy_on_request(request_handle)
                request_handle:headers():add("x-custom-header", generate_uuid())
              end

方式2：使用Envoy内置UUID过滤器 #

Envoy提供了专门的UUID过滤器，无需编写脚本即可生成UUID：

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: add-uuid-header
  namespace: istio-system
spec:
  workloadSelector:
    labels:
      istio: ingressgateway
  configPatches:
    - applyTo: HTTP_FILTER
      match:
        context: GATEWAY
        listener:
          filterChain:
            filter:
              name: "envoy.filters.network.http_connection_manager"
              subFilter:
                name: "envoy.filters.http.router"
      patch:
        operation: INSERT_BEFORE
        value:
          name: envoy.filters.http.uuid
          typed_config:
            "@type": "type.googleapis.com/envoy.extensions.filters.http.uuid.v3.UuidConfig"
            request_header_name: "x-custom-header" # 指定要添加的请求头名称
            generate_request_id: true # 启用UUID生成

为什么VirtualService中的{{ uuid() }}不生效？ #

Istio的VirtualService配置里，请求头的值仅支持静态字符串，不支持模板函数或动态变量解析，所以你输入的'{{ uuid() }}'会被当作字面量直接传递给后端服务，无法生成动态UUID。

内容的提问来源于stack exchange，提问作者aayush kumar