Load balancing with Traefik

The main use case for Traefik in this scenario is to distribute incoming HTTP(S) and TCP requests from the Internet to front-end services that can handle these requests. This tutorial shows you one such example using a demo web application.

Traefik can natively integrate with Consul using the Consul Catalog Provider and can use tags to route traffic.

Reference material

• Traefik
• Traefik Consul Catalog Provider Documentation

Prerequisites

To perform the tasks described in this tutorial, you need to have a Nomad environment with Consul installed. You can use this Terraform environment to provision a sandbox environment. This tutorial uses a cluster with one server node and three client nodes.

Create and run a demo web app job

Create a job for a demo web application and name the file webapp.nomad.hcl:

job "demo-webapp" {
  datacenters = ["dc1"]

  group "demo" {
    count = 3

    network {
      port  "http"{
        to = -1
      }
    }

    service {
      name = "demo-webapp"
      port = "http"

      tags = [
        "traefik.enable=true",
        "traefik.http.routers.http.rule=Path(`/myapp`)",
      ]

      check {
        type     = "http"
        path     = "/"
        interval = "2s"
        timeout  = "2s"
      }
    }

    task "server" {
      env {
        PORT    = "${NOMAD_PORT_http}"
        NODE_IP = "${NOMAD_IP_http}"
      }

      driver = "docker"

      config {
        image = "hashicorp/demo-webapp-lb-guide"
        ports = ["http"]
      }
    }
  }
}

• Note that this job deploys 3 instances of the demo web application which you load balance with Traefik in the next few steps.

• The job uses tags to configure routing to the web app. Even though the application listens on /, it is possible to define /myapp as the route because of the Path option.

You can now deploy the demo web application:

$ nomad run webapp.nomad.hcl
==> Monitoring evaluation "a2061ab7"
    Evaluation triggered by job "demo-webapp"
    Evaluation within deployment: "8ca6d358"
    Allocation "1d14babe" created: node "2d6eea6e", group "demo"
    Allocation "3abb950d" created: node "a62fa99d", group "demo"
    Allocation "c65e14bf" created: node "a209a662", group "demo"
    Evaluation status changed: "pending" -> "complete"
==> Evaluation "a2061ab7" finished with status "complete"

Create and run a Traefik job

Create a job named traefik.nomad.hcl. This job starts an instance of Traefik and configures it to discover its configuration from Consul. This Traefik instance provides routing and load balancing to the sample web application.

job "traefik" {
  region      = "global"
  datacenters = ["dc1"]
  type        = "service"

  group "traefik" {
    count = 1

    network {
      port "http" {
        static = 8080
      }

      port "api" {
        static = 8081
      }
    }

    service {
      name = "traefik"

      check {
        name     = "alive"
        type     = "tcp"
        port     = "http"
        interval = "10s"
        timeout  = "2s"
      }
    }

    task "traefik" {
      driver = "docker"

      config {
        image        = "traefik:v2.2"
        network_mode = "host"

        volumes = [
          "local/traefik.toml:/etc/traefik/traefik.toml",
        ]
      }

      template {
        data = <<EOF
[entryPoints]
    [entryPoints.http]
    address = ":8080"
    [entryPoints.traefik]
    address = ":8081"

[api]
    dashboard = true
    insecure  = true

# Enable Consul Catalog configuration backend.
[providers.consulCatalog]
    prefix           = "traefik"
    exposedByDefault = false

    [providers.consulCatalog.endpoint]
      address = "127.0.0.1:8500"
      scheme  = "http"
EOF

        destination = "local/traefik.toml"
      }

      resources {
        cpu    = 100
        memory = 128
      }
    }
  }
}

• This configuration uses a static port for the load balancer to 8080. This allow you to query traefik.service.consul:8080 at the appropriate paths (as configured in the tags section of webapp.nomad.hcl from anywhere inside your cluster so you can reach the web application.

• The Traefik dashboard is configured at port 8081.

• Please note that although the job contains an inline template, you could alternatively use the template stanza in conjunction with the artifact stanza to download an input template from a remote source such as an S3 bucket.

Now, run the Traefik job:

$ nomad run traefik.nomad.hcl
==> Monitoring evaluation "e22ce276"
    Evaluation triggered by job "traefik"
    Evaluation within deployment: "c6466497"
    Allocation "695c5632" created: node "a62fa99d", group "traefik"
    Evaluation status changed: "pending" -> "complete"
==> Evaluation "e22ce276" finished with status "complete"

Check the Traefik dashboard

You can visit the dashboard for Traefik at http://<Your-Traefik-IP-address>:8081. You can use this page to verify your settings and for basic monitoring.

Make a request to the load balancer

If you query the Traefik load balancer, you should be able to see a response similar to the one shown below (this command should be run from a node inside your cluster):

$ curl http://traefik.service.consul:8080/myapp
Welcome! You are on node 172.31.28.103:28893

Note that your request has been forwarded to one of the several deployed instances of the demo web application (which is spread across 3 Nomad clients). The output shows the IP address of the host it is deployed on. If you repeat your requests, the IP address changes based on which backend web server instance received the request.