145 lines
4.7 KiB
Markdown
145 lines
4.7 KiB
Markdown
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---
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tags: [kubernetes, service, ingress, networking, service-discovery]
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create time: 2026-05-18 00:30
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---
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# K8s 网络与服务发现 — Service 与 Ingress
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## 概述
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Kubernetes 的网络模型解决了容器 IP 频繁变动的问题。Service 提供**稳定的服务发现入口**，Ingress 提供**L7 HTTP 路由能力**。本文将梳理核心概念、典型模式和常见问题。
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## Service 类型
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| 类型 | 特点 | 使用场景 |
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|------|------|---------|
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| **ClusterIP** | 集群内 IP，外部不可访问 | 默认，内部服务间调用 |
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| **NodePort** | 在每个 Node 上开端口 | 调试、临时访问 |
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| **LoadBalancer** | 云厂商分配公网 IP | 对外暴露的服务 |
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| **ExternalName** | CNAME 到外部域名 | 对接外部系统 |
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### ClusterIP Service — 服务发现的载体
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```yaml
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apiVersion: v1
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kind: Service
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metadata:
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name: order-service
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spec:
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selector:
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app: order # 匹配带此 label 的 Pod
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ports:
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- port: 80 # Service 端口（对外暴露）
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targetPort: 8080 # 容器实际监听端口
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protocol: TCP
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type: ClusterIP
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```
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调用方只需 `http://order-service:80`，K8s 通过 iptables/IPVS 自动实现负载均衡。
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> [!question] Service 是怎么做到负载均衡的？
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>
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> 每个 Node 上的 kube-proxy 会监控 Service 的变动，自动生成 iptables 规则或 IPVS 虚拟服务器配置。当请求发往 ClusterIP 时，内核将其 DNAT 到后端 Pod IP 之一，负载均衡算法默认是 round-robin。K8s 1.14+ 推荐使用 IPVS 模式（`kube-proxy --proxy-mode=ipvs`），性能更高且支持更多算法。
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## Ingress — HTTP/HTTPS 路由
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```yaml
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apiVersion: networking.k8s.io/v1
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kind: Ingress
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metadata:
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name: main-ingress
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annotations:
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nginx.ingress.kubernetes.io/rewrite-target: /
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spec:
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rules:
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- host: api.example.com
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http:
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paths:
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- path: /orders
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pathType: Prefix
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backend:
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service:
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name: order-service
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port:
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number: 80
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- path: /users
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pathType: Prefix
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backend:
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service:
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name: user-service
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port:
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number: 80
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```
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> [!info] Ingress Controller 是什么？
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>
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> Ingress 只是一个 API 对象，真正的 HTTP 路由由 Ingress Controller（如 NGINX、Traefik、Envoy）执行。安装后会在集群中运行一个 LoadBalancer 类型的 Pod 集群，监听 Ingress 资源变化并生成对应配置。
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### 常见 Ingress Annotation（NGINX 为例）
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| Annotation | 用途 | 示例值 |
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|------------|------|--------|
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| `rewrite-target` | URL 重写 | `/` |
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| `ssl-redirect` | 强制 HTTPS | `"true"` |
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| `rate-limit` | 限流 | `100` |
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| `whitelist-source-range` | IP 白名单 | `10.0.0.0/8` |
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| `client-max-body-size` | 上传文件大小限制 | `50m` |
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## Headless Service — 无头服务
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Headless Service (`ClusterIP: None`) 不分配虚拟 IP，而是返回所有匹配 Pod 的真实 IP。这是 StatefulSet 的灵魂搭档：
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```yaml
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apiVersion: v1
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kind: Service
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metadata:
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name: mysql-headless
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spec:
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clusterIP: None # 关键：不分配 ClusterIP
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selector:
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app: mysql
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ports:
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- port: 3306
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```
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通过 DNS 可以直接访问单个 Pod：
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- `mysql-cluster-0.mysql-headless.production.svc.cluster.local:3306`
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- `mysql-cluster-1.mysql-headless.production.svc.cluster.local:3306`
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## K8s 网络模型总结
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```mermaid
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flowchart LR
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EXT["外部流量"] --> INGRESS["Ingress Controller"]
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INGRESS --> SVC_A["order-service:80"]
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INGRESS --> SVC_B["user-service:80"]
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SVC_A --> Pod1["order-pod-1\n10.244.1.5:8080"]
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SVC_A --> Pod2["order-pod-2\n10.244.2.3:8080"]
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SVC_B --> Pod3["user-pod-1\n10.244.1.8:3000"]
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Pod1 -->|DNS解析| COREDNS["CoreDNS<br/>svc.cluster.local"]
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style EXT fill:#e3f2fd
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style INGRESS fill:#fff3e0
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style SVC_A fill:#e8f5e9
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style SVC_B fill:#fce4ec
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```
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> [!tip] 调试技巧：Service 不通怎么办？
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>
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> 1. `kubectl get svc <name>` 确认 Service 存在且有 ClusterIP
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> 2. `kubectl get endpoints <name>` 检查 Endpoint 列表是否为空
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> 3. Endpoint 为空 → 检查 selector 标签是否匹配 Pod
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> 4. Endpoint 有值但 curl 不通 → 进入 Pod `curl <ClusterIP>:<port>` 验证
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> 5. ClusterIP 通但外部不通 → 检查 Ingress / LoadBalancer 配置
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## 关联笔记
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- [[../01-核心概念与Deployment]] — Deployment 通过 selector 与 Service 关联
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- [[../02-配置管理]] — Service 的端点配置不直接涉及 ConfigMap/Secret
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- [[../04-扩缩容与有状态应用]] — Headless Service + StatefulSet 配合
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- [[../hhs/MS/02-服务治理/04-服务发现]] — K8s Service 是服务端发现模式的代表
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