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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.

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Registering a Basic Consul Service

First, create a minimal service definition and register it with Consul.
Simulate a service restart to see how Consul handles temporary outages:
When you’re done, deregister the service:
The basic service definition offers no health checks, so Consul assumes it is always healthy.

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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:
Register the enhanced service:
Until the first TCP check passes, Consul marks the service as failing and will not return it in discovery queries.

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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.

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Simulating Failure and Recovery

To test Consul’s failure detection:
Within the next interval, the Consul UI shows the failure details: Restart Apache to restore health:
After the next 10-second interval, the TCP check passes and Consul marks the service as healthy again.

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Service Definition Comparison

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Practice Lab