DevOps

Wait4X: The Elegant Service Readiness Notifier for DevOps

Huzaif Shah

19 Apr 2025 • 4 min read

Introduction

In modern container-based architectures, one challenge is ensuring that services are ready before their dependencies attempt to use them. Wait4X is a handy CLI tool which solves this problem with a simple notification system.

What Makes Wait4X Special?

Unlike complex monitoring tools, Wait4X does one thing extremely well - it waits for services to become available and then notifies you with an exit code:

Exit code 0: Service is ready
Non-zero exit code: Service is not ready within the timeout

This simplicity makes it perfect for scripting and automation in CI/CD pipelines, docker-compose files, or Kubernetes deployment strategies.

Real-World Examples with Exit Codes

1: Checking Redis service (6380)

$ wait4x tcp localhost:6380 --timeout 3s
2025-04-10T15:16:27Z INF [TCP] Checking the localhost:6380 ...

✅ SUCCESS: Service is ready! Exit code: 0

2: Checking a port that's not in use (7777)

$ wait4x tcp localhost:7777 --timeout 3s
2025-04-10T15:16:27Z INF [TCP] Checking the localhost:7777 ...
2025-04-10T15:16:27Z ERR Expectation failed error="failed to establish a tcp connection, caused by: dial tcp [::1]:7777: connect: connection refused"
2025-04-10T15:16:28Z INF [TCP] Checking the localhost:7777 ...
2025-04-10T15:16:28Z ERR Expectation failed error="failed to establish a tcp connection, caused by: dial tcp [::1]:7777: connect: connection refused"
2025-04-10T15:16:29Z INF [TCP] Checking the localhost:7777 ...
2025-04-10T15:16:29Z ERR Expectation failed error="failed to establish a tcp connection, caused by: dial tcp [::1]:7777: connect: connection refused"
Error: context deadline exceeded
❌ FAILED: Service is not ready within the timeout. Exit code: 124

3: MySQL-specific check on port 3306

$ wait4x tcp localhost:3306 --timeout 3s
2025-04-10T15:16:30Z INF [TCP] Checking the localhost:3306 ...
✅ SUCCESS: Service is ready! Exit code: 0

4: Checking multiple services in parallel

$ wait4x tcp localhost:3306 localhost:6380 localhost:7777 --timeout 3s
2025-04-10T15:16:30Z INF [TCP] Checking the localhost:3306 ...
2025-04-10T15:16:30Z INF [TCP] Checking the localhost:6380 ...
2025-04-10T15:16:30Z INF [TCP] Checking the localhost:7777 ...
2025-04-10T15:16:30Z ERR Expectation failed error="failed to establish a tcp connection, caused by: dial tcp [::1]:7777: connect: connection refused"
2025-04-10T15:16:31Z INF [TCP] Checking the localhost:7777 ...
2025-04-10T15:16:31Z ERR Expectation failed error="failed to establish a tcp connection, caused by: dial tcp [::1]:7777: connect: connection refused"
2025-04-10T15:16:32Z INF [TCP] Checking the localhost:7777 ...
2025-04-10T15:16:32Z ERR Expectation failed error="failed to establish a tcp connection, caused by: dial tcp [::1]:7777: connect: connection refused"
Error: context deadline exceeded
❌ At least one service is not ready

5: Inverted check - waiting for a port to be free

$ wait4x tcp localhost:7777 --invert-check --timeout 3s
2025-04-10T15:16:33Z INF [TCP] Checking the localhost:7777 ...
2025-04-10T15:16:33Z ERR Expectation failed error="failed to establish a tcp connection, caused by: dial tcp [::1]:7777: connect: connection refused"
✅ SUCCESS: Service is ready! Exit code: 0$ wait4x tcp localhost:3306 --invert-check --timeout 3s

2025-04-10T15:16:33Z INF [TCP] Checking the localhost:3306 ...
2025-04-10T15:16:34Z INF [TCP] Checking the localhost:3306 ...
2025-04-10T15:16:35Z INF [TCP] Checking the localhost:3306 ...
Error: context deadline exceeded
❌ FAILED: Service is not ready within the timeout. Exit code: 124

6: Checking HTTP endpoint with expected status code

$ wait4x http https://httpbin.org/status/200 --expect-status-code 200 --timeout 5s
2025-04-10T15:16:36Z INF [HTTP] Checking the https://httpbin.org/status/200 ...
✅ SUCCESS: Service is ready! Exit code: 0

$ wait4x http https://httpbin.org/status/404 --expect-status-code 200 --timeout 5s
2025-04-10T15:16:37Z INF [HTTP] Checking the https://httpbin.org/status/404 ...
2025-04-10T15:16:40Z ERR Expectation failed error="the status code doesn't expect" actual=404 expect=200
2025-04-10T15:16:41Z INF [HTTP] Checking the https://httpbin.org/status/404 ...
2025-04-10T15:16:42Z ERR Expectation failed error="timed out while making an http call, caused by: Get \"https://httpbin.org/status/404\": context deadline exceeded" timeout=3s
Error: context deadline exceeded

❌ FAILED: Service is not ready within the timeout. Exit code: 124

Docker Integration

Example docker-compose usage:

version: '3.8'
services:
  app:
    image: my-app
    depends_on:
      - db
    command: sh -c "wait4x tcp db:5432 --timeout 30s && npm start"
  db:
    image: postgres

Kubernetes Integration

Example Kubernetes init container usage:

initContainers:
  - name: wait-for-services
    image: wait4x/wait4x
    command: ["wait4x", "tcp", "db:5432", "redis:6379"]

Best Practices

Timeouts: Set appropriate timeouts based on your environment
- Local development: 30-60 seconds
- Production: Consider network latency and service startup times
Intervals: Choose appropriate check intervals
- Too frequent: May impact performance
- Too infrequent: May delay application startup
Error Handling: Always implement proper error handling
- Log failures
- Set appropriate exit codes
- Consider retry mechanisms
Security: Handle sensitive data properly
- Use environment variables
- Consider Docker secrets in production
- Avoid hardcoding credentials

Conclusion

Wait4X is a lightweight, effective cli tool for managing service readiness in modern app deployments. It brings:

Reliability: Services are verified before startup.
Flexibility: Wide protocol and config support.
Integration: Fits naturally in Docker and Kubernetes.
Simplicity: Easy to set up and use.

At KubeNine, tools like Wait4X help us reduce downtime, prevent startup errors, and streamline service orchestration across environments. Whether you're building locally or deploying to production, adding Wait4X to your workflow is a simple step toward more resilient applications.