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| layout | page_title | sidebar_current | description |
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| guides | Load Balancing with Nomad | guides-load-balancing | There are multiple approaches to load balancing within a Nomad cluster. One approach involves using [fabio][fabio]. Fabio integrates natively with Consul and provides rich features with an optional Web UI. |
Load Balancing with Fabio
Fabio integrates natively with Consul and provides an optional Web UI to visualize routing.
The main use case for fabio is to distribute incoming HTTP(S) and TCP requests from the internet to frontend services that can handle these requests. This guide will show you one such example using Apache web server.
Reference Material
Estimated Time to Complete
20 minutes
Challenge
Think of a scenario where a Nomad operator needs to configure an environment to make Apache web server highly available behind an endpoint and distribute incoming traffic evenly.
Solution
Deploy fabio as a system scheduler so that it can route incoming traffic evenly to the Apache web server group regardless of which client nodes Apache is running on. Place all client nodes behind an AWS load balancer to provide the end user with a single endpoint for access.
Prerequisites
To perform the tasks described in this guide, you need to have a Nomad environment with Consul installed. You can use this repo to easily provision a sandbox environment. This guide will assume a cluster with one server node and three client nodes.
-> Please Note: This guide is for demo purposes and is only using a single server node. In a production cluster, 3 or 5 server nodes are recommended.
Steps
Step 1: Create a Job for Fabio
Create a job for Fabio and name it fabio.nomad
job "fabio" {
datacenters = ["dc1"]
type = "system"
group "fabio" {
task "fabio" {
driver = "docker"
config {
image = "fabiolb/fabio"
network_mode = "host"
}
resources {
cpu = 200
memory = 128
network {
mbits = 20
port "lb" {
static = 9999
}
port "ui" {
static = 9998
}
}
}
}
}
}
Setting type to system will ensure that fabio is run on all clients.
Please note that the network_mode option is set to host so that fabio can
communicate with Consul which is also running on the client nodes.
Step 2: Run the Fabio Job
We can now register our fabio job:
$ nomad job run fabio.nomad
==> 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 see the web interface for fabio. The routing table will be empty
since we 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 will get a 404 HTTP response. That will change soon.
Step 3: Create a Job for Apache Web Server
Create a job for Apache and name it webserver.nomad
job "webserver" {
datacenters = ["dc1"]
type = "service"
group "webserver" {
count = 3
restart {
attempts = 2
interval = "30m"
delay = "15s"
mode = "fail"
}
ephemeral_disk {
size = 300
}
task "apache" {
driver = "docker"
config {
image = "httpd:latest"
port_map {
http = 80
}
}
resources {
network {
mbits = 10
port "http" {}
}
}
service {
name = "apache-webserver"
tags = ["urlprefix-/"]
port = "http"
check {
name = "alive"
type = "http"
path = "/"
interval = "10s"
timeout = "2s"
}
}
}
}
}
Notice the tag in the service stanza begins with urlprefix-. This is how a
path is registered with fabio. In this case, we are registering the path '/'
with fabio (which will route us to the default page for Apache web server).
Step 4: Run the Job for Apache Web Server
We can now register our job for Apache:
$ nomad job run webserver.nomad
==> 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! At this point,
you should be able to visit any of the Nomad clients at port 9999 and
see the default web page for Apache web server. If you visit fabio's web
interface by going to any of the client nodes at port 9998, you will see that
the routing table has been populated as shown below (Note: your destination IP
addresses will be different).
Feel free to reduce the count in webserver.nomad for testing purposes. You
will see that you still get routed to the Apache home page by accessing
any client node on port 9999. Accordingly, the routing table
in the web interface on port 9999 will reflect the changes.
Step 5: Place Nomad Client Nodes Behing AWS Load Balancer
At this point, you are ready to place your Nomad client nodes behind an AWS load balancer. Your Nomad client nodes may change over time, and it is important to provide your end users with a single endpoint to access your services. This guide will use the Classic Load Balancer.
The AWS documentation provides instruction on how to create a load balancer. The basic steps involve creating a load balancer, registering instances behind the load balancer (in our case these will be the Nomad client nodes), creating listeners, and configuring health checks.
Once you are done
with this, you should be able to hit the DNS name of your load balancer at port
80 (or whichever port you configured in your listener) and see the home page of
Apache web server. If you configured your listener to also forward traffic to
the web interface at port 9998, you should be able to access that as well.
