Load balancing with Fabio

Fabio distributes incoming HTTP(S) and TCP requests from the internet to front-end services that can handle these requests. It integrates natively with Consul and provides an optional web UI to visualize routing.

Follow these steps to use Fabio as a load balancer:

1. Deploy Fabio as a system job so that it can route incoming traffic evenly to your application's server group regardless of which client nodes your application is running on.
2. Configure a urlprefix- tag in your application job specification's group.service block. Refer to the Fabio Quickstart for more information on the urlprefix- tag requirement.
3. Place all Nomad client nodes behind your cloud provider's load balancer to provide the end user with a single endpoint for access to your application.

This guide shows you how to deploy Fabio as a load balancer for an Apache web server.

Prerequisites

You must configure your Nomad installation to use Consul. Refer to the Consul integration content for more information.

Deploy Fabio as a system job

Create a job specification for Fabio and name it fabio.nomad.hcl. Note the following:

• type is system so that the job runs as a system job.
• network_mode is host so that Fabio can communicate with Consul on the client nodes.

job "fabio" {
  datacenters = ["dc1"]
  type = "system"

  group "fabio" {
    network {
      port "lb" {
        static = 9999
      }
      port "ui" {
        static = 9998
      }
    }
    task "fabio" {
      driver = "docker"
      config {
        image = "fabiolb/fabio"
        network_mode = "host"
        ports = ["lb","ui"]
      }

      resources {
        cpu    = 200
        memory = 128
      }
    }
  }
}

Deploy the Fabio job with the nomad run command.

$ nomad job run fabio.nomad.hcl
==> Monitoring evaluation "fba4f04a"
    Evaluation triggered by job "fabio"
    Allocation "6e6367d4" created: node "f3739267", group "fabio"
    Allocation "d17573b4" created: node "28d7f859", group "fabio"
    Allocation "f3ad9b16" created: node "510898b6", group "fabio"
    Evaluation status changed: "pending" -> "complete"
==> Evaluation "fba4f04a" finished with status "complete"

At this point, you should be able to visit any one of your client nodes at port 9998 and access the web interface for Fabio. The routing table should be empty because you have not yet deployed anything that Fabio can route to. Accordingly, if you visit any of the client nodes at port 9999 at this point, you get a 404 HTTP response. This error is to be expected because there are no routes built yet.

Configure your application

Create a job for the Apache web server and name it webserver.nomad.hcl. Notice the tag in the service stanza begins with urlprefix-. Fabio looks for services with that special tag and builds routes for them. In this case, the job registers the path / with Fabio. This routes incoming traffic to / to the default page for the Apache web server.

job "webserver" {
  datacenters = ["dc1"]
  type = "service"

  group "webserver" {
    count = 3
    network {
      port "http" {
        to = 80
      }
    }

    service {
      name = "apache-webserver"
      tags = ["urlprefix-/"]
      port = "http"
      check {
        name     = "alive"
        type     = "http"
        path     = "/"
        interval = "10s"
        timeout  = "2s"
      }
    }

    restart {
      attempts = 2
      interval = "30m"
      delay = "15s"
      mode = "fail"
    }

    task "apache" {
      driver = "docker"
      config {
        image = "httpd:latest"
        ports = ["http"]
      }
    }
  }
}

Deploy the Apache web server job with the nomad run command.

$ nomad job run webserver.nomad.hcl
==> Monitoring evaluation "c7bcaf40"
    Evaluation triggered by job "webserver"
    Evaluation within deployment: "e3603b50"
    Allocation "20951ad4" created: node "510898b6", group "webserver"
    Allocation "43807686" created: node "28d7f859", group "webserver"
    Allocation "7b60eb24" created: node "f3739267", group "webserver"
    Evaluation status changed: "pending" -> "complete"
==> Evaluation "c7bcaf40" finished with status "complete"

You have now deployed and registered your web servers with Fabio. You should be able to visit any of the Nomad clients at port 9999 to visit Apache's default web page. If you visit Fabio's web interface by going to any of the client nodes at port 9998, you can observe that the routing table is populated.

Place Nomad client nodes behind a cloud provider load balancer

Your Nomad client nodes may change over time, so it is important to provide your end users with a single endpoint to access your services. You may do this by placing your Nomad client nodes behind a cloud provider's load balancer, such as AWS Elastic Load Balancing (ELB), Azure Load Balancer, or Google Cloud Load Balancing.

The basic steps involve creating a load balancer, registering Nomad client nodes behind the load balancer, creating listeners, and configuring health checks. If you followed this guide, be sure to create ingress routes for Fabio.

After you configure your cloud provider's load balancer, you should be able to access the cloud load balancer DNS name:

• At port 80 to visit the Apache home page.
• At port 9998 to access the Fabio web UI.