Demo Check Service Status from the Catalog

In this guide, we’ll explore how to verify the status of your services in HashiCorp Consul using the UI, DNS interface, and HTTP API. We’ll also walk through adding a second node to the cluster and confirming that multiple service instances are correctly registered.

Viewing Services in the Consul UI

We have a client node named web-server-01 which registers the front-end-eCommerce service. On the Consul UI home screen, you’ll see two entries:

consul (2 instances)
front-end-eCommerce (1 instance)

The image shows a web interface for HashiCorp Consul, displaying two services: "consul" with two instances and "front-end-eCommerce" with one instance.

Click front-end-eCommerce to view the service details and health check (check web on port 80), which passes since Apache is running on the host.

The image shows a web interface displaying health check statuses for a server, indicating that the agent is alive and reachable, and a successful TCP connection on port 80.

Querying the Service Catalog

You can also query Consul programmatically via DNS or the HTTP API. Below is a quick comparison:

Query Method	Command	Output Format
DNS (port 8600)	`dig @<CONSUL_IP> -p 8600 front-end-eCommerce.service.consul A`	A records (IP addresses)
HTTP API (port 8500)	`curl http://<CONSUL_IP>:8500/v1/catalog/service/front-end-eCommerce?ns=default \| jq`	JSON array

DNS Lookup

Note

Consul’s built-in DNS server listens on port 8600 by default. Ensure your firewall allows UDP/TCP traffic on this port.

Run:

dig @10.0.101.110 -p 8600 front-end-eCommerce.service.consul A

Sample output:

;; ANSWER SECTION:
front-end-eCommerce.service.consul. 0 IN A 10.0.101.177

HTTP API Query

Fetch the service catalog via HTTP:

curl --request GET \
  http://54.92.155.215:8500/v1/catalog/service/front-end-eCommerce?ns=default \
  | jq

Example response:

[
  {
    "Node": "web-server-01",
    "Address": "10.0.101.177",
    "ServiceName": "front-end-eCommerce",
    "ServiceTags": ["v7.05", "production"],
    "ServiceAddress": "10.0.101.177",
    "ServiceTaggedAddresses": {
      "lan_ipv4": { "Address": "10.0.101.177", "Port": 80 }
    }
  }
]

This output shows the node name, IP address, and metadata for each instance.

Adding a Second Server

Let’s register web-server-02 with the same front-end-eCommerce service.

Step	Command	Expected Result
Start Consul agent	`sudo systemctl start consul`	Agent is running
Join the cluster	`consul join 10.0.101.110`	`web-server-02` shows in `consul members`
Register the service	`consul services register service-with-health.json`	Service appears in UI

Verifying Multiple Instances

In the UI

Refresh the Consul UI. front-end-eCommerce now displays two healthy instances: web-server-01 and web-server-02.

Via HTTP API

Re-run the catalog query:

curl http://54.92.155.215:8500/v1/catalog/service/front-end-eCommerce?ns=default | jq

You’ll see both nodes:

[
  { "Node": "web-server-01", "Address": "10.0.101.177", … },
  { "Node": "web-server-02", "Address": "10.0.101.178", … }
]

Via DNS

Query DNS again:

dig @10.0.101.110 -p 8600 front-end-eCommerce.service.consul A

Sample ANSWER SECTION:

front-end-eCommerce.service.consul. 0 IN A 10.0.101.177
front-end-eCommerce.service.consul. 0 IN A 10.0.101.178

This confirms that both Consul DNS and the HTTP API correctly reflect the two running instances.