init-c

Init Container for probing dependant services in Kubernetes

About

In certain use cases you would want to delay starting up your deployment by checking if dependent services are up either through http or tcp probing. This helps your services to boot up in the correct order, for reference check out this example. Particular use cases include service discovery and fetching startup configs for spring boot applications.

Features

• HTTP probe
• TCP Probe
• DNS Probe

Usage

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: frontend
  namespace: default
  labels:
    app: frontend
spec:
  replicas: 1
  selector:
    matchLabels:
      app: frontend
  template:
    metadata:
      labels:
        app: frontend
    spec:
      # Add your init container here            
      initContainers:
      - name: init-c
        image: jdube/init-c
        args: ['http', '-u', "http://backend.default"]
      containers:
      - name: frontend
        image: jdube/frontend
        ports:
        - containerPort: 8000

Local Testing

docker run --rm jdube/init-c http -u https://www.google.com

DNS Probe Usage

To use the DNS probe, specify dns as the probe type and use the -h or --hostname argument to provide the hostname to probe.

initContainers:
  - name: init-c
    image: jdube/init-c
    args: ['dns', '-h', "google.com"]

docker run --rm jdube/init-c dns -h google.com

TCP Probe Usage

To use the TCP probe, specify tcp as the probe type and use the -i or --ip argument to provide the IP address and -p or --port argument to provide the port to probe.

Basic TCP Probe Examples

Database Connection (PostgreSQL)

initContainers:
  - name: init-c
    image: jdube/init-c
    args: ['tcp', '-i', "database.default", '-p', "5432"]

Redis Cache

initContainers:
  - name: init-c
    image: jdube/init-c
    args: ['tcp', '-i', "redis.default", '-p', "6379"]

MySQL Database

initContainers:
  - name: init-c
    image: jdube/init-c
    args: ['tcp', '-i', "mysql.default", '-p', "3306"]

MongoDB

initContainers:
  - name: init-c
    image: jdube/init-c
    args: ['tcp', '-i', "mongodb.default", '-p', "27017"]

Custom Application Service

initContainers:
  - name: init-c
    image: jdube/init-c
    args: ['tcp', '-i', "backend-service.default", '-p', "8080"]

TCP Probe with Custom Timeout

You can specify a custom timeout using the -t or --timeout argument:

initContainers:
  - name: init-c
    image: jdube/init-c
    args: ['tcp', '-i', "database.default", '-p', "5432", '-t', "30"]

Local Testing Examples

# Test local service
docker run --rm jdube/init-c tcp -i 127.0.0.1 -p 80

# Test database connection
docker run --rm jdube/init-c tcp -i 127.0.0.1 -p 5432

# Test with custom timeout (30 seconds)
docker run --rm jdube/init-c tcp -i 127.0.0.1 -p 3306 -t 30

# Test external service
docker run --rm jdube/init-c tcp -i google.com -p 80

Complete Deployment Example with TCP Probe

Here's a complete example showing how to use TCP probes in a real deployment scenario:

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-application
  namespace: default
  labels:
    app: web-application
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web-application
  template:
    metadata:
      labels:
        app: web-application
    spec:
      # Wait for database and cache to be ready
      initContainers:
      - name: wait-for-db
        image: jdube/init-c
        args: ['tcp', '-i', "postgres.default", '-p', "5432", '-t', "60"]
      - name: wait-for-cache
        image: jdube/init-c
        args: ['tcp', '-i', "redis.default", '-p', "6379", '-t', "30"]
      containers:
      - name: web-app
        image: myapp/web-application:latest
        ports:
        - containerPort: 8080
        env:
        - name: DATABASE_URL
          value: "postgres://postgres.default:5432/myapp"
        - name: REDIS_URL
          value: "redis://redis.default:6379"

Contributing

Please read CONTRIBUTING.md for details on our code of conduct, and the process for submitting pull requests to us.

Versioning

We use SemVer for versioning. For the versions available, see the tags on this repository.