> ## Documentation Index > Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt > Use this file to discover all available pages before exploring further. # Demo Working with Health Checks > This tutorial covers enhancing a Consul service definition by adding a TCP health check and observing its status. 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. ```bash theme={null} # 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: ```bash theme={null} 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: ```bash theme={null} ec2-user@ip-10-0-101-177:~$ consul services deregister service.json Deregistered service: web-server-01 ``` The basic service definition offers no health checks, so Consul assumes it is always healthy. *** ## 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`: ```json theme={null} { "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: ```bash theme={null} ec2-user@ip-10-0-101-177:~$ consul services register service-with-health.json Registered service: front-end-eCommerce ``` Until the first TCP check passes, Consul marks the service as **failing** and will not return it in discovery queries. *** ## Observing Health Check Status 1. Open the [Consul UI](http://localhost:8500/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: ```bash theme={null} ec2-user@ip-10-0-101-177:~$ sudo systemctl stop httpd ``` Within the next interval, the Consul UI shows the failure details: | Check Name | Status | Output | | -------------------- | ------- | -------------------------------------------------- | | Check web on port 80 | failed | dial tcp 127.0.0.1:80: connect: connection refused | | Serf Health Status | passing | Agent alive and reachable | Restart Apache to restore health: ```bash theme={null} 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 | Feature | Basic Definition | With TCP Health Check | | ----------------------- | ---------------- | ----------------------------------------- | | `check` block | Not present | Present with `tcp`, `interval`, `timeout` | | Initial health status | Always passing | Marked failing until first check | | Service discoverability | Immediate | Delayed until healthy | *** ## Links and References * [Consul Health Checks Documentation](https://www.consul.io/docs/health-checks) * [Service Discovery with Consul](https://www.consul.io/docs/discovery) * [Consul CLI Reference](https://www.consul.io/docs/commands)