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 will show 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 guide, you need to have a Nomad environment with Consul installed. You can use this Terraform environment to provision a sandbox environment. This tutorial will assume a cluster with one server node and three client nodes.

»Steps

»Step 1: Create a Job for Demo Web App

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

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

  group "demo" {
    count = 3

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

      driver = "docker"

      config {
        image = "hashicorp/demo-webapp-lb-guide"
      }

      resources {
        network {
          mbits = 10
          port  "http"{}
        }
      }

      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"
        }
      }
    }
  }
}

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

• We are using tags to configure routing to our web app. Even though our application listens on /, it is possible to define /myapp as the route because of the Path option.

»Step 2: Deploy the Demo Web App

We can now deploy our demo web application:

$ nomad run webapp.nomad
==> 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"

»Step 3: Create a Job for Traefik

Create a job for Traefik and name it traefik.nomad. This will be our load balancer that will balance requests to the deployed instances of our web application.

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

  group "traefik" {
    count = 1

    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

        network {
          mbits = 10

          port "http" {
            static = 8080
          }

          port "api" {
            static = 8081
          }
        }
      }

      service {
        name = "traefik"

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

• We have statically set the port of our load balancer to 8080. This will allow us to query traefik.service.consul:8080 at the appropriate paths (as configured in the tags section of webapp.nomad from anywhere inside our cluster so we can reach our web application.

• The Traefik dashboard is configured at port 8081.

• Please note that although we have defined the template inline, we 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.

»Step 4: Run the Traefik Job

We can now register our Traefik job:

$ nomad run traefik.nomad
==> 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"

»Step 5: 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.

»Step 6: 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, you will see that the IP address changes.