Hello, my name is Alena Prokharchyk and I am a part of the software
development team at Rancher Labs. In this article I’m going to give an
overview of a new feature I’ve been working on, which was released this
week with Rancher 0.16 – a Docker Load Balancing service. One of the
most frequently requested Rancher features, load balancers are used to
distribute traffic between docker containers. Now Rancher users
can configure, update and scale up an integrated load balancing service
to meet their application needs, using either Rancher’s UI or API. To
implement our load balancing functionality we decided to use HAproxy,
which is deployed as a contianer, and managed by the Rancher
orchestration functionality. With Rancher’s Load Balancing capability,
users are now able to use a consistent, portable load balancing service
on any infrastructure where they can run Docker. Whether it is running
in a public cloud, private cloud, lab, cluster, or even on a laptop, any
container can be a target for the load balancer.
Creating a Load Balancer
Once you have an environment running in Rancher, it is simple to create
a Load Balancer. You’ll see a new top level tab in the Rancher UI
called “Balancing” from which you can create and access your load
balancers. 
To create a new load balancer click on + Add Load Balancer. You’ll
be given a configuration screen to provide details on how you want the
load balancer to function. 
There are a number of different options for configuration, and I’ve
created a video demonstration to walk through the process.
Updating an active Load Balancer
In some cases after your Load Balancer has been created, you might want
to change its settings – for example to add or remove listener ports,
configure a health check, or simply add more target containers. Rancher
performs all the updates without any downtime for your application. To
update the Load Balancer, bring up the Load Balancer “Details” view by
clicking on its name in the UI:
Then navigate to the toolbar of the setting you want to change, and
make the update:
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Understanding Health Checks
Health checks can be incredibly helpful when running a production
application. Health checks monitor the availability of target
containers, so that if one of the load balanced containers in your app
becomes unresponsive, it can be excluded from the list of balanced
hosts, until its functioning again. You can delegate this task to the
Rancher Load Balancer by configuring the health check on it from the UI.
Just provide a monitoring URL for the target container, as well as
check intervals and healthy and unhealthy response thresholds. You can
see the UI for this in the image below.
Stickiness Policies
Some applications require that a user continues to connect to the same
backend server within the same login session. This persistence is
achieved by configuring Stickiness policy on the Load Balancer. With
stickiness, you can control whether the session cookie is provided by
the application, or directly from the load balancer.
Scaling your application
The Load Balancer service is primarily used to help scale up
applications as you add additional targets to the load balancer.
However, to provide an additional layer of scaling, the load balancer
itself can also scale across multiple hosts, creating a clustered load
balancing service. With the Load Balancer deployed on multiple hosts,
you can use a Global Load Balancing service, such as Amazon Web
Services, Route 53, to distribute incoming traffic across load
balancers. This can be especially useful when running load balancers in
different physical locations. The diagram below explains how this can be
done. 
Load Balancing and Service Discovery
This new load balancing support has plenty of independent value, but it
will also be an important part of the work we’re doing on service
discovery, and support for Docker Compose. We’re still working on this
and testing it, but you should start to see this functionality in
Rancher over the next four to six weeks. If you’d like to learn about
load balancing, Docker Compose, service discovery and running
microservices with Rancher, please join our next online meetup where
we’ll be covering all of these topics by clicking the button
below. Alena Prokharchyk @lemonjet https://github.com/alena1108