DNS Proxy 和 DNS 缓存

支持的版本: Istio 1.28+ 最后更新: February 23, 2026

通过 Istio 的 DNS 管理功能优化外部服务访问性能并控制 DNS 查询。

目录

1. DNS Proxy 概述
2. DNS Proxy 与 DNS 缓存
3. DNS Proxy 配置
4. ServiceEntry 集成
5. DNS 缓存配置
6. 自动地址分配
7. 故障排除
8. 最佳实践

DNS Proxy 概述

Istio DNS Proxy 是一项功能，其中 Envoy 作为 DNS 服务器拦截并处理应用程序的 DNS 请求。

主要功能

1. DNS 查询拦截：Envoy 在 UDP 端口 53 上处理 DNS 请求
2. 基于 ServiceEntry 的解析：当外部服务注册为 ServiceEntry 时，自动生成 DNS 响应
3. 自动 IP 分配：自动为外部服务分配虚拟 IP
4. 绕过 CoreDNS：降低 Kubernetes DNS 服务器负载

架构

DNS Proxy 与 DNS 缓存

这两项功能具有不同的用途和行为：

特性	DNS Proxy	DNS 缓存
角色	充当 DNS 服务器	缓存 DNS 查询结果
行为	拦截 DNS 查询并直接响应	在外部 DNS 查询后存储结果
配置	ISTIO_META_DNS_CAPTURE	dns_refresh_rate
目标	注册在 ServiceEntry 中的服务	所有外部 DNS 查询
IP 分配	自动虚拟 IP 分配	使用实际 DNS 响应
CoreDNS	可绕过	仍会使用
Istio 版本	1.8+	所有版本

组合使用

同时使用这两项功能可提供最佳性能：

DNS Proxy 配置

1. 全局启用

将 DNS Proxy 应用于所有 namespace：

apiVersion: install.istio.io/v1alpha1
kind: IstioOperator
metadata:
  name: istio
  namespace: istio-system
spec:
  meshConfig:
    defaultConfig:
      proxyMetadata:
        # Enable DNS Proxy
        ISTIO_META_DNS_CAPTURE: "true"
        # Enable automatic IP allocation
        ISTIO_META_DNS_AUTO_ALLOCATE: "true"

2. 按 namespace 启用

仅为特定 namespace 启用：

apiVersion: v1
kind: Namespace
metadata:
  name: production
  labels:
    istio-injection: enabled
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: istio-sidecar-injector
  namespace: istio-system
data:
  values: |
    global:
      proxy:
        holdApplicationUntilProxyStarts: true
    sidecarInjectorWebhook:
      templates:
        custom: |
          spec:
            containers:
            - name: istio-proxy
              env:
              - name: ISTIO_META_DNS_CAPTURE
                value: "true"
              - name: ISTIO_META_DNS_AUTO_ALLOCATE
                value: "true"

3. 按 Pod 启用

仅为特定 Pod 启用：

apiVersion: v1
kind: Pod
metadata:
  name: myapp
  annotations:
    proxy.istio.io/config: |
      proxyMetadata:
        ISTIO_META_DNS_CAPTURE: "true"
        ISTIO_META_DNS_AUTO_ALLOCATE: "true"
spec:
  containers:
  - name: app
    image: myapp:v1

4. iptables 规则验证

启用 DNS Proxy 后，会添加以下 iptables 规则：

# Enter pod
kubectl exec -it <pod-name> -c istio-proxy -- /bin/bash

# Check DNS redirect rules
iptables -t nat -L ISTIO_OUTPUT -n -v

# Expected output
Chain ISTIO_OUTPUT (1 references)
pkts bytes target     prot opt in     out     source               destination
   0     0 RETURN     udp  --  *      *       0.0.0.0/0            127.0.0.53           udp dpt:53
   0     0 REDIRECT   udp  --  *      *       0.0.0.0/0            0.0.0.0/0            udp dpt:53 redir ports 15053

ServiceEntry 集成

DNS Proxy 与 ServiceEntry 紧密集成。

基本 ServiceEntry

apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-api
  namespace: default
spec:
  hosts:
  - api.example.com
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL
  resolution: DNS

DNS Proxy 行为：

1. 应用程序执行 api.example.com DNS 查询
2. Envoy DNS Proxy 返回虚拟 IP（例如 240.240.0.1）
3. 应用程序向虚拟 IP 发送请求
4. Envoy 转换为实际 IP 并传输

多 Host 注册

apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-services
spec:
  hosts:
  - "*.example.com"  # Wildcard supported
  - api.partner.com
  - cdn.assets.com
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  - number: 80
    name: http
    protocol: HTTP
  location: MESH_EXTERNAL
  resolution: DNS

显式 Endpoints

apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-database
spec:
  hosts:
  - database.external.com
  addresses:
  - 203.0.113.0/24  # External network range
  ports:
  - number: 3306
    name: mysql
    protocol: TCP
  location: MESH_EXTERNAL
  resolution: STATIC
  endpoints:
  - address: 203.0.113.10
  - address: 203.0.113.11
  - address: 203.0.113.12

DNS 缓存配置

DNS 缓存可提升外部 DNS 查询性能。

启用 Envoy DNS 缓存

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: dns-cache-filter
  namespace: istio-system
spec:
  configPatches:
  - applyTo: CLUSTER
    match:
      context: SIDECAR_OUTBOUND
      cluster:
        service: "*.example.com"
    patch:
      operation: MERGE
      value:
        dns_refresh_rate: 30s  # DNS cache refresh interval
        dns_lookup_family: V4_ONLY  # Use IPv4 only
        dns_failure_refresh_rate:
          base_interval: 5s  # Retry interval on failure
          max_interval: 30s

高级 DNS 缓存配置

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: advanced-dns-cache
  namespace: istio-system
spec:
  configPatches:
  - applyTo: CLUSTER
    match:
      context: SIDECAR_OUTBOUND
    patch:
      operation: MERGE
      value:
        # DNS cache TTL settings
        dns_refresh_rate: 60s

        # DNS lookup timeout
        dns_query_timeout: 5s

        # IP version priority
        dns_lookup_family: AUTO  # Auto select IPv4/IPv6

        # Cache policy on failure
        dns_failure_refresh_rate:
          base_interval: 2s
          max_interval: 10s

        # Respect DNS TTL
        respect_dns_ttl: true

仅应用于特定服务

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: api-dns-cache
  namespace: default
spec:
  workloadSelector:
    labels:
      app: frontend
  configPatches:
  - applyTo: CLUSTER
    match:
      cluster:
        service: api.external.com
    patch:
      operation: MERGE
      value:
        dns_refresh_rate: 30s
        dns_lookup_family: V4_ONLY

自动地址分配

DNS Proxy 会自动为注册在 ServiceEntry 中的服务分配虚拟 IP。

自动分配行为

地址范围配置

默认使用 240.240.0.0/16 范围。如需更改：

apiVersion: install.istio.io/v1alpha1
kind: IstioOperator
spec:
  meshConfig:
    defaultConfig:
      proxyMetadata:
        ISTIO_META_DNS_CAPTURE: "true"
        ISTIO_META_DNS_AUTO_ALLOCATE: "true"
    # Change automatic allocation address range
    defaultServiceExportTo:
    - "*"
    # Address range (example, actually managed internally by Envoy)
    outboundTrafficPolicy:
      mode: ALLOW_ANY

验证已分配的 IP

# Check allocated virtual IP in Envoy config
istioctl proxy-config clusters <pod-name> -n <namespace> --fqdn api.example.com -o json

# Example output
{
  "name": "outbound|443||api.example.com",
  "type": "STRICT_DNS",
  "connectTimeout": "10s",
  "loadAssignment": {
    "clusterName": "outbound|443||api.example.com",
    "endpoints": [{
      "lbEndpoints": [{
        "endpoint": {
          "address": {
            "socketAddress": {
              "address": "240.240.0.1",  # Virtual IP
              "portValue": 443
            }
          }
        }
      }]
    }]
  }
}

故障排除

验证 DNS Proxy 运行情况

# 1. Check DNS Proxy environment variable
kubectl get pod <pod-name> -o jsonpath='{.spec.containers[?(@.name=="istio-proxy")].env[?(@.name=="ISTIO_META_DNS_CAPTURE")].value}'

# 2. Check iptables rules
kubectl exec -it <pod-name> -c istio-proxy -- iptables -t nat -L ISTIO_OUTPUT -n | grep 15053

# 3. Verify Envoy DNS Listener
istioctl proxy-config listeners <pod-name> --port 15053

# 4. DNS query test
kubectl exec -it <pod-name> -c app -- nslookup api.example.com

# 5. Check Envoy logs
kubectl logs <pod-name> -c istio-proxy | grep -i dns

常见问题

问题 1：DNS 查询仍然发送到 CoreDNS

原因：DNS Proxy 未启用

解决方案：

# Check environment variable
kubectl get pod <pod-name> -o yaml | grep ISTIO_META_DNS_CAPTURE

# If not present, add annotation
kubectl patch deployment <deployment-name> -p '
spec:
  template:
    metadata:
      annotations:
        proxy.istio.io/config: |
          proxyMetadata:
            ISTIO_META_DNS_CAPTURE: "true"
'

# Restart pods
kubectl rollout restart deployment <deployment-name>

问题 2：ServiceEntry 未反映在 DNS Proxy 中

原因：ServiceEntry 配置错误或 xDS 同步延迟

解决方案：

# Validate ServiceEntry
istioctl analyze serviceentry <name> -n <namespace>

# Check xDS sync
istioctl proxy-status

# Verify Envoy config
istioctl proxy-config clusters <pod-name> | grep <service-name>

# Force xDS resync
kubectl delete pod -n <namespace> <pod-name>

问题 3：使用虚拟 IP 时连接失败

原因：地址冲突或路由问题

解决方案：

# Verify virtual IP allocation
istioctl proxy-config clusters <pod-name> --fqdn <service-host> -o json

# Check Listener config
istioctl proxy-config listeners <pod-name> --address 240.240.0.1

# Check Envoy logs
kubectl logs <pod-name> -c istio-proxy --tail=100 | grep -i "240.240"

# Test request
kubectl exec -it <pod-name> -c app -- curl -v http://240.240.0.1

调试工具

使用 Envoy Admin API

# Port forward to pod
kubectl port-forward <pod-name> 15000:15000

# DNS Cache statistics
curl http://localhost:15000/stats | grep dns

# Cluster status
curl http://localhost:15000/clusters

# Full config dump
curl http://localhost:15000/config_dump > config.json

数据包捕获

# Capture DNS traffic
kubectl exec -it <pod-name> -c istio-proxy -- tcpdump -i any -n port 53 -w /tmp/dns.pcap

# Download file
kubectl cp <pod-name>:/tmp/dns.pcap ./dns.pcap -c istio-proxy

# Analyze with Wireshark
wireshark dns.pcap

最佳实践

1. DNS Proxy 启用策略

推荐方法：渐进式发布

2. ServiceEntry 管理

# Create separate ServiceEntry per external service
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: payment-api
  namespace: default
  labels:
    app: payment
    team: platform
spec:
  hosts:
  - api.payment-provider.com
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL
  resolution: DNS
---
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: analytics-api
  namespace: default
  labels:
    app: analytics
    team: data
spec:
  hosts:
  - api.analytics-provider.com
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL
  resolution: DNS

3. DNS 缓存 TTL 配置

# Adjust TTL based on service characteristics
apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: dns-cache-ttl
  namespace: istio-system
spec:
  configPatches:
  # Static content (long TTL)
  - applyTo: CLUSTER
    match:
      cluster:
        service: cdn.static-assets.com
    patch:
      operation: MERGE
      value:
        dns_refresh_rate: 300s  # 5 minutes

  # Dynamic API (short TTL)
  - applyTo: CLUSTER
    match:
      cluster:
        service: api.dynamic-service.com
    patch:
      operation: MERGE
      value:
        dns_refresh_rate: 10s  # 10 seconds

4. 监控指标

# DNS Proxy activity
sum(rate(envoy_dns_cache_dns_query_attempt[5m])) by (pod)

# DNS Cache hit rate
sum(rate(envoy_dns_cache_hit[5m]))
/
sum(rate(envoy_dns_cache_dns_query_attempt[5m]))
* 100

# DNS lookup latency
histogram_quantile(0.99,
  sum(rate(envoy_dns_cache_dns_query_duration_bucket[5m])) by (le)
)

# DNS lookup failure rate
sum(rate(envoy_dns_cache_dns_query_failure[5m]))
/
sum(rate(envoy_dns_cache_dns_query_attempt[5m]))
* 100

5. 安全注意事项

# Integrate DNS Proxy with AuthorizationPolicy
apiVersion: security.istio.io/v1
kind: AuthorizationPolicy
metadata:
  name: external-api-access
  namespace: default
spec:
  selector:
    matchLabels:
      app: frontend
  action: ALLOW
  rules:
  - to:
    - operation:
        hosts:
        - api.approved-partner.com  # Only approved external services
        - cdn.trusted-cdn.com
        ports:
        - "443"
---
apiVersion: security.istio.io/v1
kind: AuthorizationPolicy
metadata:
  name: deny-all-external
  namespace: default
spec:
  action: DENY
  rules:
  - to:
    - operation:
        notHosts:
        - "*.svc.cluster.local"  # Deny all requests not to cluster internal

6. 性能调优

# Optimization for high performance environments
apiVersion: install.istio.io/v1alpha1
kind: IstioOperator
spec:
  meshConfig:
    defaultConfig:
      proxyMetadata:
        ISTIO_META_DNS_CAPTURE: "true"
        ISTIO_META_DNS_AUTO_ALLOCATE: "true"
      concurrency: 4  # Envoy worker thread count
  components:
    pilot:
      k8s:
        resources:
          requests:
            cpu: 500m
            memory: 2Gi
          limits:
            cpu: 2000m
            memory: 4Gi
        hpaSpec:
          minReplicas: 2
          maxReplicas: 5

参考资料

官方文档

• Istio DNS Proxy
• Envoy DNS 缓存
• ServiceEntry

相关文档

• Istio 架构 - DNS 处理机制
• ServiceEntry
• 出口控制