Initial commit
This commit is contained in:
Zhongwei Li
@@ -0,0 +1,753 @@
|
||||
# Kubernetes Deployment Specification Reference
|
||||
|
||||
Comprehensive reference for Kubernetes Deployment resources, covering all key fields, best practices, and common patterns.
|
||||
|
||||
## Overview
|
||||
|
||||
A Deployment provides declarative updates for Pods and ReplicaSets. It manages the desired state of your application, handling rollouts, rollbacks, and scaling operations.
|
||||
|
||||
## Complete Deployment Specification
|
||||
|
||||
```yaml
|
||||
apiVersion: apps/v1
|
||||
kind: Deployment
|
||||
metadata:
|
||||
name: my-app
|
||||
namespace: production
|
||||
labels:
|
||||
app.kubernetes.io/name: my-app
|
||||
app.kubernetes.io/version: "1.0.0"
|
||||
app.kubernetes.io/component: backend
|
||||
app.kubernetes.io/part-of: my-system
|
||||
annotations:
|
||||
description: "Main application deployment"
|
||||
contact: "backend-team@example.com"
|
||||
spec:
|
||||
# Replica management
|
||||
replicas: 3
|
||||
revisionHistoryLimit: 10
|
||||
|
||||
# Pod selection
|
||||
selector:
|
||||
matchLabels:
|
||||
app: my-app
|
||||
version: v1
|
||||
|
||||
# Update strategy
|
||||
strategy:
|
||||
type: RollingUpdate
|
||||
rollingUpdate:
|
||||
maxSurge: 1
|
||||
maxUnavailable: 0
|
||||
|
||||
# Minimum time for pod to be ready
|
||||
minReadySeconds: 10
|
||||
|
||||
# Deployment will fail if it doesn't progress in this time
|
||||
progressDeadlineSeconds: 600
|
||||
|
||||
# Pod template
|
||||
template:
|
||||
metadata:
|
||||
labels:
|
||||
app: my-app
|
||||
version: v1
|
||||
annotations:
|
||||
prometheus.io/scrape: "true"
|
||||
prometheus.io/port: "9090"
|
||||
spec:
|
||||
# Service account for RBAC
|
||||
serviceAccountName: my-app
|
||||
|
||||
# Security context for the pod
|
||||
securityContext:
|
||||
runAsNonRoot: true
|
||||
runAsUser: 1000
|
||||
fsGroup: 1000
|
||||
seccompProfile:
|
||||
type: RuntimeDefault
|
||||
|
||||
# Init containers run before main containers
|
||||
initContainers:
|
||||
- name: init-db
|
||||
image: busybox:1.36
|
||||
command: ['sh', '-c', 'until nc -z db-service 5432; do sleep 1; done']
|
||||
securityContext:
|
||||
allowPrivilegeEscalation: false
|
||||
runAsNonRoot: true
|
||||
runAsUser: 1000
|
||||
|
||||
# Main containers
|
||||
containers:
|
||||
- name: app
|
||||
image: myapp:1.0.0
|
||||
imagePullPolicy: IfNotPresent
|
||||
|
||||
# Container ports
|
||||
ports:
|
||||
- name: http
|
||||
containerPort: 8080
|
||||
protocol: TCP
|
||||
- name: metrics
|
||||
containerPort: 9090
|
||||
protocol: TCP
|
||||
|
||||
# Environment variables
|
||||
env:
|
||||
- name: POD_NAME
|
||||
valueFrom:
|
||||
fieldRef:
|
||||
fieldPath: metadata.name
|
||||
- name: POD_NAMESPACE
|
||||
valueFrom:
|
||||
fieldRef:
|
||||
fieldPath: metadata.namespace
|
||||
- name: DATABASE_URL
|
||||
valueFrom:
|
||||
secretKeyRef:
|
||||
name: db-credentials
|
||||
key: url
|
||||
|
||||
# ConfigMap and Secret references
|
||||
envFrom:
|
||||
- configMapRef:
|
||||
name: app-config
|
||||
- secretRef:
|
||||
name: app-secrets
|
||||
|
||||
# Resource requests and limits
|
||||
resources:
|
||||
requests:
|
||||
memory: "256Mi"
|
||||
cpu: "250m"
|
||||
limits:
|
||||
memory: "512Mi"
|
||||
cpu: "500m"
|
||||
|
||||
# Liveness probe
|
||||
livenessProbe:
|
||||
httpGet:
|
||||
path: /health/live
|
||||
port: http
|
||||
httpHeaders:
|
||||
- name: Custom-Header
|
||||
value: Awesome
|
||||
initialDelaySeconds: 30
|
||||
periodSeconds: 10
|
||||
timeoutSeconds: 5
|
||||
successThreshold: 1
|
||||
failureThreshold: 3
|
||||
|
||||
# Readiness probe
|
||||
readinessProbe:
|
||||
httpGet:
|
||||
path: /health/ready
|
||||
port: http
|
||||
initialDelaySeconds: 5
|
||||
periodSeconds: 5
|
||||
timeoutSeconds: 3
|
||||
successThreshold: 1
|
||||
failureThreshold: 3
|
||||
|
||||
# Startup probe (for slow-starting containers)
|
||||
startupProbe:
|
||||
httpGet:
|
||||
path: /health/startup
|
||||
port: http
|
||||
initialDelaySeconds: 0
|
||||
periodSeconds: 10
|
||||
timeoutSeconds: 3
|
||||
successThreshold: 1
|
||||
failureThreshold: 30
|
||||
|
||||
# Volume mounts
|
||||
volumeMounts:
|
||||
- name: data
|
||||
mountPath: /var/lib/app
|
||||
- name: config
|
||||
mountPath: /etc/app
|
||||
readOnly: true
|
||||
- name: tmp
|
||||
mountPath: /tmp
|
||||
|
||||
# Security context for container
|
||||
securityContext:
|
||||
allowPrivilegeEscalation: false
|
||||
readOnlyRootFilesystem: true
|
||||
runAsNonRoot: true
|
||||
runAsUser: 1000
|
||||
capabilities:
|
||||
drop:
|
||||
- ALL
|
||||
|
||||
# Lifecycle hooks
|
||||
lifecycle:
|
||||
postStart:
|
||||
exec:
|
||||
command: ["/bin/sh", "-c", "echo Container started > /tmp/started"]
|
||||
preStop:
|
||||
exec:
|
||||
command: ["/bin/sh", "-c", "sleep 15"]
|
||||
|
||||
# Volumes
|
||||
volumes:
|
||||
- name: data
|
||||
persistentVolumeClaim:
|
||||
claimName: app-data
|
||||
- name: config
|
||||
configMap:
|
||||
name: app-config
|
||||
- name: tmp
|
||||
emptyDir: {}
|
||||
|
||||
# DNS configuration
|
||||
dnsPolicy: ClusterFirst
|
||||
dnsConfig:
|
||||
options:
|
||||
- name: ndots
|
||||
value: "2"
|
||||
|
||||
# Scheduling
|
||||
nodeSelector:
|
||||
disktype: ssd
|
||||
|
||||
affinity:
|
||||
podAntiAffinity:
|
||||
preferredDuringSchedulingIgnoredDuringExecution:
|
||||
- weight: 100
|
||||
podAffinityTerm:
|
||||
labelSelector:
|
||||
matchExpressions:
|
||||
- key: app
|
||||
operator: In
|
||||
values:
|
||||
- my-app
|
||||
topologyKey: kubernetes.io/hostname
|
||||
|
||||
tolerations:
|
||||
- key: "app"
|
||||
operator: "Equal"
|
||||
value: "my-app"
|
||||
effect: "NoSchedule"
|
||||
|
||||
# Termination
|
||||
terminationGracePeriodSeconds: 30
|
||||
|
||||
# Image pull secrets
|
||||
imagePullSecrets:
|
||||
- name: regcred
|
||||
```
|
||||
|
||||
## Field Reference
|
||||
|
||||
### Metadata Fields
|
||||
|
||||
#### Required Fields
|
||||
- `apiVersion`: `apps/v1` (current stable version)
|
||||
- `kind`: `Deployment`
|
||||
- `metadata.name`: Unique name within namespace
|
||||
|
||||
#### Recommended Metadata
|
||||
- `metadata.namespace`: Target namespace (defaults to `default`)
|
||||
- `metadata.labels`: Key-value pairs for organization
|
||||
- `metadata.annotations`: Non-identifying metadata
|
||||
|
||||
### Spec Fields
|
||||
|
||||
#### Replica Management
|
||||
|
||||
**`replicas`** (integer, default: 1)
|
||||
- Number of desired pod instances
|
||||
- Best practice: Use 3+ for production high availability
|
||||
- Can be scaled manually or via HorizontalPodAutoscaler
|
||||
|
||||
**`revisionHistoryLimit`** (integer, default: 10)
|
||||
- Number of old ReplicaSets to retain for rollback
|
||||
- Set to 0 to disable rollback capability
|
||||
- Reduces storage overhead for long-running deployments
|
||||
|
||||
#### Update Strategy
|
||||
|
||||
**`strategy.type`** (string)
|
||||
- `RollingUpdate` (default): Gradual pod replacement
|
||||
- `Recreate`: Delete all pods before creating new ones
|
||||
|
||||
**`strategy.rollingUpdate.maxSurge`** (int or percent, default: 25%)
|
||||
- Maximum pods above desired replicas during update
|
||||
- Example: With 3 replicas and maxSurge=1, up to 4 pods during update
|
||||
|
||||
**`strategy.rollingUpdate.maxUnavailable`** (int or percent, default: 25%)
|
||||
- Maximum pods below desired replicas during update
|
||||
- Set to 0 for zero-downtime deployments
|
||||
- Cannot be 0 if maxSurge is 0
|
||||
|
||||
**Best practices:**
|
||||
```yaml
|
||||
# Zero-downtime deployment
|
||||
strategy:
|
||||
type: RollingUpdate
|
||||
rollingUpdate:
|
||||
maxSurge: 1
|
||||
maxUnavailable: 0
|
||||
|
||||
# Fast deployment (can have brief downtime)
|
||||
strategy:
|
||||
type: RollingUpdate
|
||||
rollingUpdate:
|
||||
maxSurge: 2
|
||||
maxUnavailable: 1
|
||||
|
||||
# Complete replacement
|
||||
strategy:
|
||||
type: Recreate
|
||||
```
|
||||
|
||||
#### Pod Template
|
||||
|
||||
**`template.metadata.labels`**
|
||||
- Must include labels matching `spec.selector.matchLabels`
|
||||
- Add version labels for blue/green deployments
|
||||
- Include standard Kubernetes labels
|
||||
|
||||
**`template.spec.containers`** (required)
|
||||
- Array of container specifications
|
||||
- At least one container required
|
||||
- Each container needs unique name
|
||||
|
||||
#### Container Configuration
|
||||
|
||||
**Image Management:**
|
||||
```yaml
|
||||
containers:
|
||||
- name: app
|
||||
image: registry.example.com/myapp:1.0.0
|
||||
imagePullPolicy: IfNotPresent # or Always, Never
|
||||
```
|
||||
|
||||
Image pull policies:
|
||||
- `IfNotPresent`: Pull if not cached (default for tagged images)
|
||||
- `Always`: Always pull (default for :latest)
|
||||
- `Never`: Never pull, fail if not cached
|
||||
|
||||
**Port Declarations:**
|
||||
```yaml
|
||||
ports:
|
||||
- name: http # Named for referencing in Service
|
||||
containerPort: 8080
|
||||
protocol: TCP # TCP (default), UDP, or SCTP
|
||||
hostPort: 8080 # Optional: Bind to host port (rarely used)
|
||||
```
|
||||
|
||||
#### Resource Management
|
||||
|
||||
**Requests vs Limits:**
|
||||
|
||||
```yaml
|
||||
resources:
|
||||
requests:
|
||||
memory: "256Mi" # Guaranteed resources
|
||||
cpu: "250m" # 0.25 CPU cores
|
||||
limits:
|
||||
memory: "512Mi" # Maximum allowed
|
||||
cpu: "500m" # 0.5 CPU cores
|
||||
```
|
||||
|
||||
**QoS Classes (determined automatically):**
|
||||
|
||||
1. **Guaranteed**: requests = limits for all containers
|
||||
- Highest priority
|
||||
- Last to be evicted
|
||||
|
||||
2. **Burstable**: requests < limits or only requests set
|
||||
- Medium priority
|
||||
- Evicted before Guaranteed
|
||||
|
||||
3. **BestEffort**: No requests or limits set
|
||||
- Lowest priority
|
||||
- First to be evicted
|
||||
|
||||
**Best practices:**
|
||||
- Always set requests in production
|
||||
- Set limits to prevent resource monopolization
|
||||
- Memory limits should be 1.5-2x requests
|
||||
- CPU limits can be higher for bursty workloads
|
||||
|
||||
#### Health Checks
|
||||
|
||||
**Probe Types:**
|
||||
|
||||
1. **startupProbe** - For slow-starting applications
|
||||
```yaml
|
||||
startupProbe:
|
||||
httpGet:
|
||||
path: /health/startup
|
||||
port: 8080
|
||||
initialDelaySeconds: 0
|
||||
periodSeconds: 10
|
||||
failureThreshold: 30 # 5 minutes to start (10s * 30)
|
||||
```
|
||||
|
||||
2. **livenessProbe** - Restarts unhealthy containers
|
||||
```yaml
|
||||
livenessProbe:
|
||||
httpGet:
|
||||
path: /health/live
|
||||
port: 8080
|
||||
initialDelaySeconds: 30
|
||||
periodSeconds: 10
|
||||
timeoutSeconds: 5
|
||||
failureThreshold: 3 # Restart after 3 failures
|
||||
```
|
||||
|
||||
3. **readinessProbe** - Controls traffic routing
|
||||
```yaml
|
||||
readinessProbe:
|
||||
httpGet:
|
||||
path: /health/ready
|
||||
port: 8080
|
||||
initialDelaySeconds: 5
|
||||
periodSeconds: 5
|
||||
failureThreshold: 3 # Remove from service after 3 failures
|
||||
```
|
||||
|
||||
**Probe Mechanisms:**
|
||||
|
||||
```yaml
|
||||
# HTTP GET
|
||||
httpGet:
|
||||
path: /health
|
||||
port: 8080
|
||||
httpHeaders:
|
||||
- name: Authorization
|
||||
value: Bearer token
|
||||
|
||||
# TCP Socket
|
||||
tcpSocket:
|
||||
port: 3306
|
||||
|
||||
# Command execution
|
||||
exec:
|
||||
command:
|
||||
- cat
|
||||
- /tmp/healthy
|
||||
|
||||
# gRPC (Kubernetes 1.24+)
|
||||
grpc:
|
||||
port: 9090
|
||||
service: my.service.health.v1.Health
|
||||
```
|
||||
|
||||
**Probe Timing Parameters:**
|
||||
|
||||
- `initialDelaySeconds`: Wait before first probe
|
||||
- `periodSeconds`: How often to probe
|
||||
- `timeoutSeconds`: Probe timeout
|
||||
- `successThreshold`: Successes needed to mark healthy (1 for liveness/startup)
|
||||
- `failureThreshold`: Failures before taking action
|
||||
|
||||
#### Security Context
|
||||
|
||||
**Pod-level security context:**
|
||||
```yaml
|
||||
spec:
|
||||
securityContext:
|
||||
runAsNonRoot: true
|
||||
runAsUser: 1000
|
||||
runAsGroup: 1000
|
||||
fsGroup: 1000
|
||||
fsGroupChangePolicy: OnRootMismatch
|
||||
seccompProfile:
|
||||
type: RuntimeDefault
|
||||
```
|
||||
|
||||
**Container-level security context:**
|
||||
```yaml
|
||||
containers:
|
||||
- name: app
|
||||
securityContext:
|
||||
allowPrivilegeEscalation: false
|
||||
readOnlyRootFilesystem: true
|
||||
runAsNonRoot: true
|
||||
runAsUser: 1000
|
||||
capabilities:
|
||||
drop:
|
||||
- ALL
|
||||
add:
|
||||
- NET_BIND_SERVICE # Only if needed
|
||||
```
|
||||
|
||||
**Security best practices:**
|
||||
- Always run as non-root (`runAsNonRoot: true`)
|
||||
- Drop all capabilities and add only needed ones
|
||||
- Use read-only root filesystem when possible
|
||||
- Enable seccomp profile
|
||||
- Disable privilege escalation
|
||||
|
||||
#### Volumes
|
||||
|
||||
**Volume Types:**
|
||||
|
||||
```yaml
|
||||
volumes:
|
||||
# PersistentVolumeClaim
|
||||
- name: data
|
||||
persistentVolumeClaim:
|
||||
claimName: app-data
|
||||
|
||||
# ConfigMap
|
||||
- name: config
|
||||
configMap:
|
||||
name: app-config
|
||||
items:
|
||||
- key: app.properties
|
||||
path: application.properties
|
||||
|
||||
# Secret
|
||||
- name: secrets
|
||||
secret:
|
||||
secretName: app-secrets
|
||||
defaultMode: 0400
|
||||
|
||||
# EmptyDir (ephemeral)
|
||||
- name: cache
|
||||
emptyDir:
|
||||
sizeLimit: 1Gi
|
||||
|
||||
# HostPath (avoid in production)
|
||||
- name: host-data
|
||||
hostPath:
|
||||
path: /data
|
||||
type: DirectoryOrCreate
|
||||
```
|
||||
|
||||
#### Scheduling
|
||||
|
||||
**Node Selection:**
|
||||
|
||||
```yaml
|
||||
# Simple node selector
|
||||
nodeSelector:
|
||||
disktype: ssd
|
||||
zone: us-west-1a
|
||||
|
||||
# Node affinity (more expressive)
|
||||
affinity:
|
||||
nodeAffinity:
|
||||
requiredDuringSchedulingIgnoredDuringExecution:
|
||||
nodeSelectorTerms:
|
||||
- matchExpressions:
|
||||
- key: kubernetes.io/arch
|
||||
operator: In
|
||||
values:
|
||||
- amd64
|
||||
- arm64
|
||||
```
|
||||
|
||||
**Pod Affinity/Anti-Affinity:**
|
||||
|
||||
```yaml
|
||||
# Spread pods across nodes
|
||||
affinity:
|
||||
podAntiAffinity:
|
||||
requiredDuringSchedulingIgnoredDuringExecution:
|
||||
- labelSelector:
|
||||
matchLabels:
|
||||
app: my-app
|
||||
topologyKey: kubernetes.io/hostname
|
||||
|
||||
# Co-locate with database
|
||||
affinity:
|
||||
podAffinity:
|
||||
preferredDuringSchedulingIgnoredDuringExecution:
|
||||
- weight: 100
|
||||
podAffinityTerm:
|
||||
labelSelector:
|
||||
matchLabels:
|
||||
app: database
|
||||
topologyKey: kubernetes.io/hostname
|
||||
```
|
||||
|
||||
**Tolerations:**
|
||||
|
||||
```yaml
|
||||
tolerations:
|
||||
- key: "node.kubernetes.io/unreachable"
|
||||
operator: "Exists"
|
||||
effect: "NoExecute"
|
||||
tolerationSeconds: 30
|
||||
- key: "dedicated"
|
||||
operator: "Equal"
|
||||
value: "database"
|
||||
effect: "NoSchedule"
|
||||
```
|
||||
|
||||
## Common Patterns
|
||||
|
||||
### High Availability Deployment
|
||||
|
||||
```yaml
|
||||
spec:
|
||||
replicas: 3
|
||||
strategy:
|
||||
type: RollingUpdate
|
||||
rollingUpdate:
|
||||
maxSurge: 1
|
||||
maxUnavailable: 0
|
||||
template:
|
||||
spec:
|
||||
affinity:
|
||||
podAntiAffinity:
|
||||
requiredDuringSchedulingIgnoredDuringExecution:
|
||||
- labelSelector:
|
||||
matchLabels:
|
||||
app: my-app
|
||||
topologyKey: kubernetes.io/hostname
|
||||
topologySpreadConstraints:
|
||||
- maxSkew: 1
|
||||
topologyKey: topology.kubernetes.io/zone
|
||||
whenUnsatisfiable: DoNotSchedule
|
||||
labelSelector:
|
||||
matchLabels:
|
||||
app: my-app
|
||||
```
|
||||
|
||||
### Sidecar Container Pattern
|
||||
|
||||
```yaml
|
||||
spec:
|
||||
template:
|
||||
spec:
|
||||
containers:
|
||||
- name: app
|
||||
image: myapp:1.0.0
|
||||
volumeMounts:
|
||||
- name: shared-logs
|
||||
mountPath: /var/log
|
||||
- name: log-forwarder
|
||||
image: fluent-bit:2.0
|
||||
volumeMounts:
|
||||
- name: shared-logs
|
||||
mountPath: /var/log
|
||||
readOnly: true
|
||||
volumes:
|
||||
- name: shared-logs
|
||||
emptyDir: {}
|
||||
```
|
||||
|
||||
### Init Container for Dependencies
|
||||
|
||||
```yaml
|
||||
spec:
|
||||
template:
|
||||
spec:
|
||||
initContainers:
|
||||
- name: wait-for-db
|
||||
image: busybox:1.36
|
||||
command:
|
||||
- sh
|
||||
- -c
|
||||
- |
|
||||
until nc -z database-service 5432; do
|
||||
echo "Waiting for database..."
|
||||
sleep 2
|
||||
done
|
||||
- name: run-migrations
|
||||
image: myapp:1.0.0
|
||||
command: ["./migrate", "up"]
|
||||
env:
|
||||
- name: DATABASE_URL
|
||||
valueFrom:
|
||||
secretKeyRef:
|
||||
name: db-credentials
|
||||
key: url
|
||||
containers:
|
||||
- name: app
|
||||
image: myapp:1.0.0
|
||||
```
|
||||
|
||||
## Best Practices
|
||||
|
||||
### Production Checklist
|
||||
|
||||
- [ ] Set resource requests and limits
|
||||
- [ ] Implement all three probe types (startup, liveness, readiness)
|
||||
- [ ] Use specific image tags (not :latest)
|
||||
- [ ] Configure security context (non-root, read-only filesystem)
|
||||
- [ ] Set replica count >= 3 for HA
|
||||
- [ ] Configure pod anti-affinity for spread
|
||||
- [ ] Set appropriate update strategy (maxUnavailable: 0 for zero-downtime)
|
||||
- [ ] Use ConfigMaps and Secrets for configuration
|
||||
- [ ] Add standard labels and annotations
|
||||
- [ ] Configure graceful shutdown (preStop hook, terminationGracePeriodSeconds)
|
||||
- [ ] Set revisionHistoryLimit for rollback capability
|
||||
- [ ] Use ServiceAccount with minimal RBAC permissions
|
||||
|
||||
### Performance Tuning
|
||||
|
||||
**Fast startup:**
|
||||
```yaml
|
||||
spec:
|
||||
minReadySeconds: 5
|
||||
strategy:
|
||||
rollingUpdate:
|
||||
maxSurge: 2
|
||||
maxUnavailable: 1
|
||||
```
|
||||
|
||||
**Zero-downtime updates:**
|
||||
```yaml
|
||||
spec:
|
||||
minReadySeconds: 10
|
||||
strategy:
|
||||
rollingUpdate:
|
||||
maxSurge: 1
|
||||
maxUnavailable: 0
|
||||
```
|
||||
|
||||
**Graceful shutdown:**
|
||||
```yaml
|
||||
spec:
|
||||
template:
|
||||
spec:
|
||||
terminationGracePeriodSeconds: 60
|
||||
containers:
|
||||
- name: app
|
||||
lifecycle:
|
||||
preStop:
|
||||
exec:
|
||||
command: ["/bin/sh", "-c", "sleep 15 && kill -SIGTERM 1"]
|
||||
```
|
||||
|
||||
## Troubleshooting
|
||||
|
||||
### Common Issues
|
||||
|
||||
**Pods not starting:**
|
||||
```bash
|
||||
kubectl describe deployment <name>
|
||||
kubectl get pods -l app=<app-name>
|
||||
kubectl describe pod <pod-name>
|
||||
kubectl logs <pod-name>
|
||||
```
|
||||
|
||||
**ImagePullBackOff:**
|
||||
- Check image name and tag
|
||||
- Verify imagePullSecrets
|
||||
- Check registry credentials
|
||||
|
||||
**CrashLoopBackOff:**
|
||||
- Check container logs
|
||||
- Verify liveness probe is not too aggressive
|
||||
- Check resource limits
|
||||
- Verify application dependencies
|
||||
|
||||
**Deployment stuck in progress:**
|
||||
- Check progressDeadlineSeconds
|
||||
- Verify readiness probes
|
||||
- Check resource availability
|
||||
|
||||
## Related Resources
|
||||
|
||||
- [Kubernetes Deployment API Reference](https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.28/#deployment-v1-apps)
|
||||
- [Pod Security Standards](https://kubernetes.io/docs/concepts/security/pod-security-standards/)
|
||||
- [Resource Management](https://kubernetes.io/docs/concepts/configuration/manage-resources-containers/)
|
||||
@@ -0,0 +1,724 @@
|
||||
# Kubernetes Service Specification Reference
|
||||
|
||||
Comprehensive reference for Kubernetes Service resources, covering service types, networking, load balancing, and service discovery patterns.
|
||||
|
||||
## Overview
|
||||
|
||||
A Service provides stable network endpoints for accessing Pods. Services enable loose coupling between microservices by providing service discovery and load balancing.
|
||||
|
||||
## Service Types
|
||||
|
||||
### 1. ClusterIP (Default)
|
||||
|
||||
Exposes the service on an internal cluster IP. Only reachable from within the cluster.
|
||||
|
||||
```yaml
|
||||
apiVersion: v1
|
||||
kind: Service
|
||||
metadata:
|
||||
name: backend-service
|
||||
namespace: production
|
||||
spec:
|
||||
type: ClusterIP
|
||||
selector:
|
||||
app: backend
|
||||
ports:
|
||||
- name: http
|
||||
port: 80
|
||||
targetPort: 8080
|
||||
protocol: TCP
|
||||
sessionAffinity: None
|
||||
```
|
||||
|
||||
**Use cases:**
|
||||
- Internal microservice communication
|
||||
- Database services
|
||||
- Internal APIs
|
||||
- Message queues
|
||||
|
||||
### 2. NodePort
|
||||
|
||||
Exposes the service on each Node's IP at a static port (30000-32767 range).
|
||||
|
||||
```yaml
|
||||
apiVersion: v1
|
||||
kind: Service
|
||||
metadata:
|
||||
name: frontend-service
|
||||
spec:
|
||||
type: NodePort
|
||||
selector:
|
||||
app: frontend
|
||||
ports:
|
||||
- name: http
|
||||
port: 80
|
||||
targetPort: 8080
|
||||
nodePort: 30080 # Optional, auto-assigned if omitted
|
||||
protocol: TCP
|
||||
```
|
||||
|
||||
**Use cases:**
|
||||
- Development/testing external access
|
||||
- Small deployments without load balancer
|
||||
- Direct node access requirements
|
||||
|
||||
**Limitations:**
|
||||
- Limited port range (30000-32767)
|
||||
- Must handle node failures
|
||||
- No built-in load balancing across nodes
|
||||
|
||||
### 3. LoadBalancer
|
||||
|
||||
Exposes the service using a cloud provider's load balancer.
|
||||
|
||||
```yaml
|
||||
apiVersion: v1
|
||||
kind: Service
|
||||
metadata:
|
||||
name: public-api
|
||||
annotations:
|
||||
service.beta.kubernetes.io/aws-load-balancer-type: "nlb"
|
||||
service.beta.kubernetes.io/aws-load-balancer-scheme: "internet-facing"
|
||||
spec:
|
||||
type: LoadBalancer
|
||||
selector:
|
||||
app: api
|
||||
ports:
|
||||
- name: https
|
||||
port: 443
|
||||
targetPort: 8443
|
||||
protocol: TCP
|
||||
loadBalancerSourceRanges:
|
||||
- 203.0.113.0/24
|
||||
```
|
||||
|
||||
**Cloud-specific annotations:**
|
||||
|
||||
**AWS:**
|
||||
```yaml
|
||||
annotations:
|
||||
service.beta.kubernetes.io/aws-load-balancer-type: "nlb" # or "external"
|
||||
service.beta.kubernetes.io/aws-load-balancer-scheme: "internet-facing"
|
||||
service.beta.kubernetes.io/aws-load-balancer-cross-zone-load-balancing-enabled: "true"
|
||||
service.beta.kubernetes.io/aws-load-balancer-ssl-cert: "arn:aws:acm:..."
|
||||
service.beta.kubernetes.io/aws-load-balancer-backend-protocol: "http"
|
||||
```
|
||||
|
||||
**Azure:**
|
||||
```yaml
|
||||
annotations:
|
||||
service.beta.kubernetes.io/azure-load-balancer-internal: "true"
|
||||
service.beta.kubernetes.io/azure-pip-name: "my-public-ip"
|
||||
```
|
||||
|
||||
**GCP:**
|
||||
```yaml
|
||||
annotations:
|
||||
cloud.google.com/load-balancer-type: "Internal"
|
||||
cloud.google.com/backend-config: '{"default": "my-backend-config"}'
|
||||
```
|
||||
|
||||
### 4. ExternalName
|
||||
|
||||
Maps service to external DNS name (CNAME record).
|
||||
|
||||
```yaml
|
||||
apiVersion: v1
|
||||
kind: Service
|
||||
metadata:
|
||||
name: external-db
|
||||
spec:
|
||||
type: ExternalName
|
||||
externalName: db.external.example.com
|
||||
ports:
|
||||
- port: 5432
|
||||
```
|
||||
|
||||
**Use cases:**
|
||||
- Accessing external services
|
||||
- Service migration scenarios
|
||||
- Multi-cluster service references
|
||||
|
||||
## Complete Service Specification
|
||||
|
||||
```yaml
|
||||
apiVersion: v1
|
||||
kind: Service
|
||||
metadata:
|
||||
name: my-service
|
||||
namespace: production
|
||||
labels:
|
||||
app: my-app
|
||||
tier: backend
|
||||
annotations:
|
||||
description: "Main application service"
|
||||
prometheus.io/scrape: "true"
|
||||
spec:
|
||||
# Service type
|
||||
type: ClusterIP
|
||||
|
||||
# Pod selector
|
||||
selector:
|
||||
app: my-app
|
||||
version: v1
|
||||
|
||||
# Ports configuration
|
||||
ports:
|
||||
- name: http
|
||||
port: 80 # Service port
|
||||
targetPort: 8080 # Container port (or named port)
|
||||
protocol: TCP # TCP, UDP, or SCTP
|
||||
|
||||
# Session affinity
|
||||
sessionAffinity: ClientIP
|
||||
sessionAffinityConfig:
|
||||
clientIP:
|
||||
timeoutSeconds: 10800
|
||||
|
||||
# IP configuration
|
||||
clusterIP: 10.0.0.10 # Optional: specific IP
|
||||
clusterIPs:
|
||||
- 10.0.0.10
|
||||
ipFamilies:
|
||||
- IPv4
|
||||
ipFamilyPolicy: SingleStack
|
||||
|
||||
# External traffic policy
|
||||
externalTrafficPolicy: Local
|
||||
|
||||
# Internal traffic policy
|
||||
internalTrafficPolicy: Local
|
||||
|
||||
# Health check
|
||||
healthCheckNodePort: 30000
|
||||
|
||||
# Load balancer config (for type: LoadBalancer)
|
||||
loadBalancerIP: 203.0.113.100
|
||||
loadBalancerSourceRanges:
|
||||
- 203.0.113.0/24
|
||||
|
||||
# External IPs
|
||||
externalIPs:
|
||||
- 80.11.12.10
|
||||
|
||||
# Publishing strategy
|
||||
publishNotReadyAddresses: false
|
||||
```
|
||||
|
||||
## Port Configuration
|
||||
|
||||
### Named Ports
|
||||
|
||||
Use named ports in Pods for flexibility:
|
||||
|
||||
**Deployment:**
|
||||
```yaml
|
||||
spec:
|
||||
template:
|
||||
spec:
|
||||
containers:
|
||||
- name: app
|
||||
ports:
|
||||
- name: http
|
||||
containerPort: 8080
|
||||
- name: metrics
|
||||
containerPort: 9090
|
||||
```
|
||||
|
||||
**Service:**
|
||||
```yaml
|
||||
spec:
|
||||
ports:
|
||||
- name: http
|
||||
port: 80
|
||||
targetPort: http # References named port
|
||||
- name: metrics
|
||||
port: 9090
|
||||
targetPort: metrics
|
||||
```
|
||||
|
||||
### Multiple Ports
|
||||
|
||||
```yaml
|
||||
spec:
|
||||
ports:
|
||||
- name: http
|
||||
port: 80
|
||||
targetPort: 8080
|
||||
protocol: TCP
|
||||
- name: https
|
||||
port: 443
|
||||
targetPort: 8443
|
||||
protocol: TCP
|
||||
- name: grpc
|
||||
port: 9090
|
||||
targetPort: 9090
|
||||
protocol: TCP
|
||||
```
|
||||
|
||||
## Session Affinity
|
||||
|
||||
### None (Default)
|
||||
|
||||
Distributes requests randomly across pods.
|
||||
|
||||
```yaml
|
||||
spec:
|
||||
sessionAffinity: None
|
||||
```
|
||||
|
||||
### ClientIP
|
||||
|
||||
Routes requests from same client IP to same pod.
|
||||
|
||||
```yaml
|
||||
spec:
|
||||
sessionAffinity: ClientIP
|
||||
sessionAffinityConfig:
|
||||
clientIP:
|
||||
timeoutSeconds: 10800 # 3 hours
|
||||
```
|
||||
|
||||
**Use cases:**
|
||||
- Stateful applications
|
||||
- Session-based applications
|
||||
- WebSocket connections
|
||||
|
||||
## Traffic Policies
|
||||
|
||||
### External Traffic Policy
|
||||
|
||||
**Cluster (Default):**
|
||||
```yaml
|
||||
spec:
|
||||
externalTrafficPolicy: Cluster
|
||||
```
|
||||
- Load balances across all nodes
|
||||
- May add extra network hop
|
||||
- Source IP is masked
|
||||
|
||||
**Local:**
|
||||
```yaml
|
||||
spec:
|
||||
externalTrafficPolicy: Local
|
||||
```
|
||||
- Traffic goes only to pods on receiving node
|
||||
- Preserves client source IP
|
||||
- Better performance (no extra hop)
|
||||
- May cause imbalanced load
|
||||
|
||||
### Internal Traffic Policy
|
||||
|
||||
```yaml
|
||||
spec:
|
||||
internalTrafficPolicy: Local # or Cluster
|
||||
```
|
||||
|
||||
Controls traffic routing for cluster-internal clients.
|
||||
|
||||
## Headless Services
|
||||
|
||||
Service without cluster IP for direct pod access.
|
||||
|
||||
```yaml
|
||||
apiVersion: v1
|
||||
kind: Service
|
||||
metadata:
|
||||
name: database
|
||||
spec:
|
||||
clusterIP: None # Headless
|
||||
selector:
|
||||
app: database
|
||||
ports:
|
||||
- port: 5432
|
||||
targetPort: 5432
|
||||
```
|
||||
|
||||
**Use cases:**
|
||||
- StatefulSet pod discovery
|
||||
- Direct pod-to-pod communication
|
||||
- Custom load balancing
|
||||
- Database clusters
|
||||
|
||||
**DNS returns:**
|
||||
- Individual pod IPs instead of service IP
|
||||
- Format: `<pod-name>.<service-name>.<namespace>.svc.cluster.local`
|
||||
|
||||
## Service Discovery
|
||||
|
||||
### DNS
|
||||
|
||||
**ClusterIP Service:**
|
||||
```
|
||||
<service-name>.<namespace>.svc.cluster.local
|
||||
```
|
||||
|
||||
Example:
|
||||
```bash
|
||||
curl http://backend-service.production.svc.cluster.local
|
||||
```
|
||||
|
||||
**Within same namespace:**
|
||||
```bash
|
||||
curl http://backend-service
|
||||
```
|
||||
|
||||
**Headless Service (returns pod IPs):**
|
||||
```
|
||||
<pod-name>.<service-name>.<namespace>.svc.cluster.local
|
||||
```
|
||||
|
||||
### Environment Variables
|
||||
|
||||
Kubernetes injects service info into pods:
|
||||
|
||||
```bash
|
||||
# Service host and port
|
||||
BACKEND_SERVICE_SERVICE_HOST=10.0.0.100
|
||||
BACKEND_SERVICE_SERVICE_PORT=80
|
||||
|
||||
# For named ports
|
||||
BACKEND_SERVICE_SERVICE_PORT_HTTP=80
|
||||
```
|
||||
|
||||
**Note:** Pods must be created after the service for env vars to be injected.
|
||||
|
||||
## Load Balancing
|
||||
|
||||
### Algorithms
|
||||
|
||||
Kubernetes uses random selection by default. For advanced load balancing:
|
||||
|
||||
**Service Mesh (Istio example):**
|
||||
```yaml
|
||||
apiVersion: networking.istio.io/v1beta1
|
||||
kind: DestinationRule
|
||||
metadata:
|
||||
name: my-destination-rule
|
||||
spec:
|
||||
host: my-service
|
||||
trafficPolicy:
|
||||
loadBalancer:
|
||||
simple: LEAST_REQUEST # or ROUND_ROBIN, RANDOM, PASSTHROUGH
|
||||
connectionPool:
|
||||
tcp:
|
||||
maxConnections: 100
|
||||
```
|
||||
|
||||
### Connection Limits
|
||||
|
||||
Use pod disruption budgets and resource limits:
|
||||
|
||||
```yaml
|
||||
apiVersion: policy/v1
|
||||
kind: PodDisruptionBudget
|
||||
metadata:
|
||||
name: my-app-pdb
|
||||
spec:
|
||||
minAvailable: 2
|
||||
selector:
|
||||
matchLabels:
|
||||
app: my-app
|
||||
```
|
||||
|
||||
## Service Mesh Integration
|
||||
|
||||
### Istio Virtual Service
|
||||
|
||||
```yaml
|
||||
apiVersion: networking.istio.io/v1beta1
|
||||
kind: VirtualService
|
||||
metadata:
|
||||
name: my-service
|
||||
spec:
|
||||
hosts:
|
||||
- my-service
|
||||
http:
|
||||
- match:
|
||||
- headers:
|
||||
version:
|
||||
exact: v2
|
||||
route:
|
||||
- destination:
|
||||
host: my-service
|
||||
subset: v2
|
||||
- route:
|
||||
- destination:
|
||||
host: my-service
|
||||
subset: v1
|
||||
weight: 90
|
||||
- destination:
|
||||
host: my-service
|
||||
subset: v2
|
||||
weight: 10
|
||||
```
|
||||
|
||||
## Common Patterns
|
||||
|
||||
### Pattern 1: Internal Microservice
|
||||
|
||||
```yaml
|
||||
apiVersion: v1
|
||||
kind: Service
|
||||
metadata:
|
||||
name: user-service
|
||||
namespace: backend
|
||||
labels:
|
||||
app: user-service
|
||||
tier: backend
|
||||
spec:
|
||||
type: ClusterIP
|
||||
selector:
|
||||
app: user-service
|
||||
ports:
|
||||
- name: http
|
||||
port: 8080
|
||||
targetPort: http
|
||||
protocol: TCP
|
||||
- name: grpc
|
||||
port: 9090
|
||||
targetPort: grpc
|
||||
protocol: TCP
|
||||
```
|
||||
|
||||
### 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
|
||||
```
|
||||
|
||||
### 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