Docker Container Monitoring

Docker containers run your applications, but a "running" container isn't the same as a "working" service. External monitoring verifies that your containerized applications actually respond to requests correctly.

Why external Docker monitoring matters

Container status isn't service status

A container can be "healthy" according to Docker while the application inside is broken—database connection failures, deadlocks, or resource exhaustion don't always crash containers.

Orchestrators hide failures

Docker Swarm and Kubernetes restart failed containers automatically. Without external monitoring, you might not know your service crashed and restarted 50 times today.

Network and routing issues

Containers can be healthy but unreachable due to network configuration, load balancer issues, or DNS problems. External monitoring catches these infrastructure-level failures.

What to monitor in Docker environments

Monitoring patterns for Docker

Health check endpoints

Expose a /health or /healthz endpoint that verifies internal dependencies (database, cache, external services). Monitor this endpoint externally.

# Example: Add to your Docker cron job
0 * * * * /app/hourly-task.sh && curl -fsS https://updog.watch/ping/YOUR_TOKEN

Heartbeat monitoring for cron

Add a curl command at the end of scheduled tasks. If the task fails or doesn't run, the heartbeat monitor will alert you.

# In your docker-compose.yml cron service
command: >
  sh -c "run-my-task && curl -fsS https://updog.watch/ping/YOUR_TOKEN"

Multi-service monitoring

For microservices architectures, monitor each service's public endpoint. This tells you which specific service is failing, not just that "something is wrong."

Docker Compose example

Here's a typical monitoring setup for a Docker Compose application:

services:
  web:
    image: myapp:latest
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:8080/health"]
      interval: 30s
      timeout: 10s
      retries: 3

  cron:
    image: myapp:latest
    command: >
      sh -c "while true; do
        /app/process-jobs.sh && curl -fsS https://updog.watch/ping/TOKEN;
        sleep 3600;
      done"

Then configure UpDog to monitor https://your-app.com/health for the web service, and set up a heartbeat monitor expecting pings every hour for the cron job.

FAQ

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Related resources

• Kubernetes CronJob monitoring
• Heartbeat monitoring
• Port monitoring
• Cron job monitoring