Consul Service Discovery

Example setup

We will consider an example setup with 3 machines with the following characteristics.

See also

HashiCorp's Vagrant

Install the Consul Server

We will install a Consul server on a machine and run it as a Systemd service.

1. Download and install Consul on your Consul server machine.

   For example, on a Debian-based Linux distribution:

   $ curl -fsSL https://apt.releases.hashicorp.com/gpg | sudo apt-key add -
   $ sudo apt-add-repository \
       "deb [arch=amd64] https://apt.releases.hashicorp.com $(lsb_release -cs) main"
   $ sudo apt-get update && sudo apt-get install consul

2. Replace the content of the /etc/consul.d/consul.hcl configuration file with the following.

   datacenter = "dc1"
   server = true
   data_dir = "/opt/consul/"
   bind_addr = "192.168.50.21"
   client_addr = "192.168.50.21"
   bootstrap = true
   bootstrap_expect = 1
   
   ui_config {
     enabled = true
   }
   
   enable_syslog = true
   log_level = "INFO"

   Notable fields	Value	Description
   datacenter	Consul datacenter name	The private networking environment all Consul agents belong to.
   server	true	This Consul agent will run in server mode.
   bind_addr and client_addr	Consul server machine's static IP address	IP address Consul agents will connect to when they join the cluster.

3. Start Consul.

   $ sudo systemctl enable consul
   $ sudo systemctl start consul

4. To check if the Consul server is up and running, open the Consul web UI at http://<Consul Server IP address>:8500 in a web browser.

   Check available nodes and services.

   

See also

Consul documentation

Install a Consul agent on your web server machine

We will install and run a Consul agent on the web server machine.

1. Install Consul and create the following /etc/consul.d/consul.hcl file.

   datacenter = "dc1"
   server = false
   data_dir = "/opt/consul/"
   bind_addr = "192.168.50.22"
   retry_join = ["192.168.50.21"]
   enable_syslog = true
   log_level = "INFO"

   Notable fields	Value	Description
   datacenter	Consul datacenter name	The private networking environment all Consul agents belong to.
   server	false	This Consul agent will not run in server mode.
   bind_addr	Web server machine's static IP address	IP address Consul agents will connect to when they join the cluster.
   retry_join	Web server machine's static IP address	IP address of the Consul server, which the agent uses to join the Consul cluster.

2. Start the Consul agent.

   $ sudo systemctl enable consul
   $ sudo systemctl start consul

3. To check if the Consul agent is up and running, open the Consul web UI at http://<Consul Server IP address>:8500 in a web browser.

   Check available nodes.

   

The webserver node was created but does not contain any service as yet.

Register the web server as a service

We will register the web server as a Consul service.

1. Create a Consul service configuration file on the web server machine.

   For example, create the web.json file with the following contents:

   {
     "service": {
   
       "name": "web",
       "port": 80
     }
   }

   Field	Description
   port	Port of the listening web server.
   name	Name that will display in the Consul registry.

   To add more servers to the same backend, register more services with Consul. Keep the same name, web, in their JSON files.

2. Register your web server as a Consul service.

   $ consul services register web.json

3. To check if the service was registered, open the Consul web UI at http://<Consul Server IP address>:8500 in a web browser.

   To check the details of the service, click its name in the Services tab.

   

See also

Consul Services

Enable service discovery in HAProxy Enterprise

We will install the HAProxy Enterprise Data Plane API on the load balancer machine.

1. Follow the steps to install the HAProxy Data Plane API on your HAProxy Enterprise server.

2. To enable HAProxy Enterprise to use the Consul API, send a POST request to the HAProxy Enterprise Data Plane API's /v2/services_discovery/consul endpoint.

   $ curl -u admin:adminpwd \
       -H 'Content-Type: application/json' \
       -d '{
         "address": "192.168.50.21",
         "port": 8500,
         "enabled": true,
         "retry_timeout": 10
       }' http://192.168.50.20:5555/v2/service_discovery/consul

   The body of the request is a JSON string with the following fields:

   Field	Description
   address	The Consul server's IP address.
   port	The Consul server's HTTP API port (i.e. 8500).
   enabled	Whether to enable this integration.
   retry_timeout	Duration in seconds in-between requesting data from the Consul server.

   The HAProxy Enterprise Data Plane API now begins monitoring Consul's service catalog.

3. Check the /etc/hapee-1.6/hapee-lb.cfg file.

   A new backend section contains the web server.

   backend consul-backend-192.168.50.21-8500-web
     server SRV_V2u4y 192.168.50.22:80 check weight 128
     server SRV_1NQXA 127.0.0.1:80 disabled weight 128
     server SRV_DWcAP 127.0.0.1:80 disabled weight 128
     server SRV_IIcqg 127.0.0.1:80 disabled weight 128

   The HAProxy Enterprise Data Plane API has also added several disabled server lines.

   When you register more instances of the same service, HAProxy Enterprise fills in disabled server slots. You can thus scale up or down without a reload, in most cases.

You can now configure a frontend section that routes traffic to this backend pool of servers.

See also

Data Plane API installation