Demo Working with Health Checks

In this tutorial, we’ll walk through enhancing a Consul service definition by adding a TCP health check. You will learn how to:

• Register a basic Consul service
• Add a TCP health check on port 80
• Observe and interpret the service’s health status in the Consul UI

Prerequisites
You need a running Consul agent and an Apache HTTP server on your node.

Registering a Basic Consul Service

First, create a minimal service definition and register it with Consul.

# Open the service definition file
ec2-user@ip-10-0-101-177:~$ vi service.json

# Register the service
ec2-user@ip-10-0-101-177:~$ consul services register service.json
Registered service: front-end-eCommerce

Simulate a service restart to see how Consul handles temporary outages:

ec2-user@ip-10-0-101-177:~$ sudo systemctl stop httpd
ec2-user@ip-10-0-101-177:~$ sudo systemctl start httpd

When you’re done, deregister the service:

ec2-user@ip-10-0-101-177:~$ consul services deregister service.json
Deregistered service: web-server-01

Adding a TCP Health Check

To ensure only healthy instances are returned by service discovery, update the definition to include a TCP health check on port 80. Save the following as service-with-health.json:

{
  "node_name": "web-server-01",
  "service": {
    "id": "web-server-01",
    "name": "front-end-eCommerce",
    "tags": ["v7.05", "production"],
    "address": "10.0.101.177",
    "port": 80,
    "check": {
      "id": "web",
      "name": "Check web on port 80",
      "tcp": "localhost:80",
      "interval": "10s",
      "timeout": "1s"
    }
  }
}

Register the enhanced service:

ec2-user@ip-10-0-101-177:~$ consul services register service-with-health.json
Registered service: front-end-eCommerce

Observing Health Check Status

1. Open the Consul UI.
2. Look for the front-end-eCommerce entry under Services.
3. If the check is still pending or failing, you’ll see a red “X” icon.

After approximately 10 seconds, Consul performs the TCP check against localhost:80. A successful connection flips the status to passing, indicated by a green checkmark.

Simulating Failure and Recovery

To test Consul’s failure detection:

ec2-user@ip-10-0-101-177:~$ sudo systemctl stop httpd

Within the next interval, the Consul UI shows the failure details:

Restart Apache to restore health:

ec2-user@ip-10-0-101-177:~$ sudo systemctl start httpd

After the next 10-second interval, the TCP check passes and Consul marks the service as healthy again.

Service Definition Comparison

Links and References

• Consul Health Checks Documentation
• Service Discovery with Consul
• Consul CLI Reference