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Zhongwei Li
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skills/k8s-manifest-generator/references/service-spec.md
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skills/k8s-manifest-generator/references/service-spec.md
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# Kubernetes Service Specification Reference
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Comprehensive reference for Kubernetes Service resources, covering service types, networking, load balancing, and service discovery patterns.
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## Overview
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A Service provides stable network endpoints for accessing Pods. Services enable loose coupling between microservices by providing service discovery and load balancing.
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## Service Types
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### 1. ClusterIP (Default)
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Exposes the service on an internal cluster IP. Only reachable from within the cluster.
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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: backend-service
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namespace: production
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spec:
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type: ClusterIP
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selector:
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app: backend
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ports:
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- name: http
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port: 80
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targetPort: 8080
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protocol: TCP
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sessionAffinity: None
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```
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**Use cases:**
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- Internal microservice communication
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- Database services
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- Internal APIs
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- Message queues
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### 2. NodePort
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Exposes the service on each Node's IP at a static port (30000-32767 range).
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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: frontend-service
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spec:
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type: NodePort
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selector:
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app: frontend
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ports:
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- name: http
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port: 80
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targetPort: 8080
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nodePort: 30080 # Optional, auto-assigned if omitted
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protocol: TCP
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```
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**Use cases:**
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- Development/testing external access
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- Small deployments without load balancer
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- Direct node access requirements
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**Limitations:**
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- Limited port range (30000-32767)
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- Must handle node failures
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- No built-in load balancing across nodes
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### 3. LoadBalancer
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Exposes the service using a cloud provider's load balancer.
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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: public-api
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annotations:
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service.beta.kubernetes.io/aws-load-balancer-type: "nlb"
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service.beta.kubernetes.io/aws-load-balancer-scheme: "internet-facing"
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spec:
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type: LoadBalancer
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selector:
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app: api
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ports:
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- name: https
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port: 443
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targetPort: 8443
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protocol: TCP
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loadBalancerSourceRanges:
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- 203.0.113.0/24
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```
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**Cloud-specific annotations:**
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**AWS:**
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```yaml
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annotations:
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service.beta.kubernetes.io/aws-load-balancer-type: "nlb" # or "external"
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service.beta.kubernetes.io/aws-load-balancer-scheme: "internet-facing"
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service.beta.kubernetes.io/aws-load-balancer-cross-zone-load-balancing-enabled: "true"
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service.beta.kubernetes.io/aws-load-balancer-ssl-cert: "arn:aws:acm:..."
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service.beta.kubernetes.io/aws-load-balancer-backend-protocol: "http"
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```
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**Azure:**
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```yaml
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annotations:
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service.beta.kubernetes.io/azure-load-balancer-internal: "true"
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service.beta.kubernetes.io/azure-pip-name: "my-public-ip"
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```
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**GCP:**
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```yaml
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annotations:
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cloud.google.com/load-balancer-type: "Internal"
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cloud.google.com/backend-config: '{"default": "my-backend-config"}'
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```
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### 4. ExternalName
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Maps service to external DNS name (CNAME record).
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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: external-db
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spec:
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type: ExternalName
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externalName: db.external.example.com
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ports:
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- port: 5432
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```
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**Use cases:**
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- Accessing external services
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- Service migration scenarios
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- Multi-cluster service references
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## Complete Service Specification
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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: my-service
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namespace: production
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labels:
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app: my-app
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tier: backend
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annotations:
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description: "Main application service"
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prometheus.io/scrape: "true"
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spec:
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# Service type
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type: ClusterIP
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# Pod selector
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selector:
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app: my-app
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version: v1
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# Ports configuration
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ports:
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- name: http
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port: 80 # Service port
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targetPort: 8080 # Container port (or named port)
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protocol: TCP # TCP, UDP, or SCTP
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# Session affinity
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sessionAffinity: ClientIP
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sessionAffinityConfig:
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clientIP:
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timeoutSeconds: 10800
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# IP configuration
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clusterIP: 10.0.0.10 # Optional: specific IP
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clusterIPs:
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- 10.0.0.10
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ipFamilies:
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- IPv4
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ipFamilyPolicy: SingleStack
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# External traffic policy
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externalTrafficPolicy: Local
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# Internal traffic policy
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internalTrafficPolicy: Local
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# Health check
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healthCheckNodePort: 30000
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# Load balancer config (for type: LoadBalancer)
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loadBalancerIP: 203.0.113.100
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loadBalancerSourceRanges:
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- 203.0.113.0/24
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# External IPs
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externalIPs:
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- 80.11.12.10
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# Publishing strategy
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publishNotReadyAddresses: false
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```
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## Port Configuration
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### Named Ports
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Use named ports in Pods for flexibility:
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**Deployment:**
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```yaml
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spec:
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template:
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spec:
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containers:
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- name: app
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ports:
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- name: http
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containerPort: 8080
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- name: metrics
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containerPort: 9090
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```
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**Service:**
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```yaml
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spec:
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ports:
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- name: http
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port: 80
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targetPort: http # References named port
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- name: metrics
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port: 9090
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targetPort: metrics
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```
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### Multiple Ports
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```yaml
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spec:
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ports:
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- name: http
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port: 80
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targetPort: 8080
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protocol: TCP
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- name: https
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port: 443
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targetPort: 8443
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protocol: TCP
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- name: grpc
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port: 9090
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targetPort: 9090
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protocol: TCP
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```
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## Session Affinity
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### None (Default)
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Distributes requests randomly across pods.
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```yaml
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spec:
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sessionAffinity: None
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```
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### ClientIP
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Routes requests from same client IP to same pod.
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```yaml
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spec:
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sessionAffinity: ClientIP
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sessionAffinityConfig:
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clientIP:
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timeoutSeconds: 10800 # 3 hours
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```
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**Use cases:**
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- Stateful applications
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- Session-based applications
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- WebSocket connections
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## Traffic Policies
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### External Traffic Policy
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**Cluster (Default):**
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```yaml
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spec:
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externalTrafficPolicy: Cluster
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```
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- Load balances across all nodes
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- May add extra network hop
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- Source IP is masked
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**Local:**
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```yaml
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spec:
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externalTrafficPolicy: Local
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```
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- Traffic goes only to pods on receiving node
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- Preserves client source IP
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- Better performance (no extra hop)
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- May cause imbalanced load
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### Internal Traffic Policy
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```yaml
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spec:
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internalTrafficPolicy: Local # or Cluster
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```
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Controls traffic routing for cluster-internal clients.
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## Headless Services
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Service without cluster IP for direct pod access.
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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: database
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spec:
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clusterIP: None # Headless
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selector:
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app: database
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ports:
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- port: 5432
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targetPort: 5432
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```
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**Use cases:**
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- StatefulSet pod discovery
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- Direct pod-to-pod communication
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- Custom load balancing
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- Database clusters
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**DNS returns:**
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- Individual pod IPs instead of service IP
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- Format: `<pod-name>.<service-name>.<namespace>.svc.cluster.local`
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## Service Discovery
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### DNS
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**ClusterIP Service:**
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```
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<service-name>.<namespace>.svc.cluster.local
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```
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Example:
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```bash
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curl http://backend-service.production.svc.cluster.local
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```
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**Within same namespace:**
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```bash
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curl http://backend-service
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```
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**Headless Service (returns pod IPs):**
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```
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<pod-name>.<service-name>.<namespace>.svc.cluster.local
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```
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### Environment Variables
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Kubernetes injects service info into pods:
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```bash
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# Service host and port
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BACKEND_SERVICE_SERVICE_HOST=10.0.0.100
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BACKEND_SERVICE_SERVICE_PORT=80
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# For named ports
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BACKEND_SERVICE_SERVICE_PORT_HTTP=80
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```
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**Note:** Pods must be created after the service for env vars to be injected.
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## Load Balancing
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### Algorithms
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Kubernetes uses random selection by default. For advanced load balancing:
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**Service Mesh (Istio example):**
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```yaml
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apiVersion: networking.istio.io/v1beta1
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kind: DestinationRule
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metadata:
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name: my-destination-rule
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spec:
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host: my-service
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trafficPolicy:
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loadBalancer:
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simple: LEAST_REQUEST # or ROUND_ROBIN, RANDOM, PASSTHROUGH
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connectionPool:
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tcp:
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maxConnections: 100
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```
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### Connection Limits
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Use pod disruption budgets and resource limits:
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|
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```yaml
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apiVersion: policy/v1
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kind: PodDisruptionBudget
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metadata:
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name: my-app-pdb
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spec:
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minAvailable: 2
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selector:
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matchLabels:
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app: my-app
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```
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## Service Mesh Integration
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### Istio Virtual Service
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```yaml
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apiVersion: networking.istio.io/v1beta1
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kind: VirtualService
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metadata:
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name: my-service
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spec:
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hosts:
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- my-service
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http:
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- match:
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- headers:
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version:
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exact: v2
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route:
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- destination:
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host: my-service
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subset: v2
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- route:
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- destination:
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host: my-service
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subset: v1
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weight: 90
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- destination:
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host: my-service
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subset: v2
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weight: 10
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```
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## Common Patterns
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|
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### Pattern 1: Internal Microservice
|
||||
|
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```yaml
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apiVersion: v1
|
||||
kind: Service
|
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metadata:
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name: user-service
|
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namespace: backend
|
||||
labels:
|
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app: user-service
|
||||
tier: backend
|
||||
spec:
|
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type: ClusterIP
|
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selector:
|
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app: user-service
|
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ports:
|
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- name: http
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port: 8080
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targetPort: http
|
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protocol: TCP
|
||||
- name: grpc
|
||||
port: 9090
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targetPort: grpc
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protocol: TCP
|
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```
|
||||
|
||||
### Pattern 2: Public API with Load Balancer
|
||||
|
||||
```yaml
|
||||
apiVersion: v1
|
||||
kind: Service
|
||||
metadata:
|
||||
name: api-gateway
|
||||
annotations:
|
||||
service.beta.kubernetes.io/aws-load-balancer-type: "nlb"
|
||||
service.beta.kubernetes.io/aws-load-balancer-ssl-cert: "arn:aws:acm:..."
|
||||
spec:
|
||||
type: LoadBalancer
|
||||
externalTrafficPolicy: Local
|
||||
selector:
|
||||
app: api-gateway
|
||||
ports:
|
||||
- name: https
|
||||
port: 443
|
||||
targetPort: 8443
|
||||
protocol: TCP
|
||||
loadBalancerSourceRanges:
|
||||
- 0.0.0.0/0
|
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```
|
||||
|
||||
### Pattern 3: StatefulSet with Headless Service
|
||||
|
||||
```yaml
|
||||
apiVersion: v1
|
||||
kind: Service
|
||||
metadata:
|
||||
name: cassandra
|
||||
spec:
|
||||
clusterIP: None
|
||||
selector:
|
||||
app: cassandra
|
||||
ports:
|
||||
- port: 9042
|
||||
targetPort: 9042
|
||||
---
|
||||
apiVersion: apps/v1
|
||||
kind: StatefulSet
|
||||
metadata:
|
||||
name: cassandra
|
||||
spec:
|
||||
serviceName: cassandra
|
||||
replicas: 3
|
||||
selector:
|
||||
matchLabels:
|
||||
app: cassandra
|
||||
template:
|
||||
metadata:
|
||||
labels:
|
||||
app: cassandra
|
||||
spec:
|
||||
containers:
|
||||
- name: cassandra
|
||||
image: cassandra:4.0
|
||||
```
|
||||
|
||||
### Pattern 4: External Service Mapping
|
||||
|
||||
```yaml
|
||||
apiVersion: v1
|
||||
kind: Service
|
||||
metadata:
|
||||
name: external-database
|
||||
spec:
|
||||
type: ExternalName
|
||||
externalName: prod-db.cxyz.us-west-2.rds.amazonaws.com
|
||||
---
|
||||
# Or with Endpoints for IP-based external service
|
||||
apiVersion: v1
|
||||
kind: Service
|
||||
metadata:
|
||||
name: external-api
|
||||
spec:
|
||||
ports:
|
||||
- port: 443
|
||||
targetPort: 443
|
||||
protocol: TCP
|
||||
---
|
||||
apiVersion: v1
|
||||
kind: Endpoints
|
||||
metadata:
|
||||
name: external-api
|
||||
subsets:
|
||||
- addresses:
|
||||
- ip: 203.0.113.100
|
||||
ports:
|
||||
- port: 443
|
||||
```
|
||||
|
||||
### Pattern 5: Multi-Port Service with Metrics
|
||||
|
||||
```yaml
|
||||
apiVersion: v1
|
||||
kind: Service
|
||||
metadata:
|
||||
name: web-app
|
||||
annotations:
|
||||
prometheus.io/scrape: "true"
|
||||
prometheus.io/port: "9090"
|
||||
prometheus.io/path: "/metrics"
|
||||
spec:
|
||||
type: ClusterIP
|
||||
selector:
|
||||
app: web-app
|
||||
ports:
|
||||
- name: http
|
||||
port: 80
|
||||
targetPort: 8080
|
||||
- name: metrics
|
||||
port: 9090
|
||||
targetPort: 9090
|
||||
```
|
||||
|
||||
## Network Policies
|
||||
|
||||
Control traffic to services:
|
||||
|
||||
```yaml
|
||||
apiVersion: networking.k8s.io/v1
|
||||
kind: NetworkPolicy
|
||||
metadata:
|
||||
name: allow-frontend-to-backend
|
||||
spec:
|
||||
podSelector:
|
||||
matchLabels:
|
||||
app: backend
|
||||
policyTypes:
|
||||
- Ingress
|
||||
ingress:
|
||||
- from:
|
||||
- podSelector:
|
||||
matchLabels:
|
||||
app: frontend
|
||||
ports:
|
||||
- protocol: TCP
|
||||
port: 8080
|
||||
```
|
||||
|
||||
## Best Practices
|
||||
|
||||
### Service Configuration
|
||||
|
||||
1. **Use named ports** for flexibility
|
||||
2. **Set appropriate service type** based on exposure needs
|
||||
3. **Use labels and selectors consistently** across Deployments and Services
|
||||
4. **Configure session affinity** for stateful apps
|
||||
5. **Set external traffic policy to Local** for IP preservation
|
||||
6. **Use headless services** for StatefulSets
|
||||
7. **Implement network policies** for security
|
||||
8. **Add monitoring annotations** for observability
|
||||
|
||||
### Production Checklist
|
||||
|
||||
- [ ] Service type appropriate for use case
|
||||
- [ ] Selector matches pod labels
|
||||
- [ ] Named ports used for clarity
|
||||
- [ ] Session affinity configured if needed
|
||||
- [ ] Traffic policy set appropriately
|
||||
- [ ] Load balancer annotations configured (if applicable)
|
||||
- [ ] Source IP ranges restricted (for public services)
|
||||
- [ ] Health check configuration validated
|
||||
- [ ] Monitoring annotations added
|
||||
- [ ] Network policies defined
|
||||
|
||||
### Performance Tuning
|
||||
|
||||
**For high traffic:**
|
||||
```yaml
|
||||
spec:
|
||||
externalTrafficPolicy: Local
|
||||
sessionAffinity: ClientIP
|
||||
sessionAffinityConfig:
|
||||
clientIP:
|
||||
timeoutSeconds: 3600
|
||||
```
|
||||
|
||||
**For WebSocket/long connections:**
|
||||
```yaml
|
||||
spec:
|
||||
sessionAffinity: ClientIP
|
||||
sessionAffinityConfig:
|
||||
clientIP:
|
||||
timeoutSeconds: 86400 # 24 hours
|
||||
```
|
||||
|
||||
## Troubleshooting
|
||||
|
||||
### Service not accessible
|
||||
|
||||
```bash
|
||||
# Check service exists
|
||||
kubectl get service <service-name>
|
||||
|
||||
# Check endpoints (should show pod IPs)
|
||||
kubectl get endpoints <service-name>
|
||||
|
||||
# Describe service
|
||||
kubectl describe service <service-name>
|
||||
|
||||
# Check if pods match selector
|
||||
kubectl get pods -l app=<app-name>
|
||||
```
|
||||
|
||||
**Common issues:**
|
||||
- Selector doesn't match pod labels
|
||||
- No pods running (endpoints empty)
|
||||
- Ports misconfigured
|
||||
- Network policy blocking traffic
|
||||
|
||||
### DNS resolution failing
|
||||
|
||||
```bash
|
||||
# Test DNS from pod
|
||||
kubectl run debug --rm -it --image=busybox -- nslookup <service-name>
|
||||
|
||||
# Check CoreDNS
|
||||
kubectl get pods -n kube-system -l k8s-app=kube-dns
|
||||
kubectl logs -n kube-system -l k8s-app=kube-dns
|
||||
```
|
||||
|
||||
### Load balancer issues
|
||||
|
||||
```bash
|
||||
# Check load balancer status
|
||||
kubectl describe service <service-name>
|
||||
|
||||
# Check events
|
||||
kubectl get events --sort-by='.lastTimestamp'
|
||||
|
||||
# Verify cloud provider configuration
|
||||
kubectl describe node
|
||||
```
|
||||
|
||||
## Related Resources
|
||||
|
||||
- [Kubernetes Service API Reference](https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.28/#service-v1-core)
|
||||
- [Service Networking](https://kubernetes.io/docs/concepts/services-networking/service/)
|
||||
- [DNS for Services and Pods](https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/)
|
||||
Reference in New Issue
Block a user