Rolling your own servers with Kubernetes

https://gravitational.com/blog/aws_vs_colocation/

May 5, 2019
by Ev Kontsevoy

Why leave AWS?

In this three-part blog series, we’ll try to address some of the fears and
uncertainties faced by organizations who had successfully started their projects
on public clouds, like AWS, but for one reason or another found themselves needing to replicate their cloud environment from scratch, starting with an
empty rack in their own enterprise server room or a colocation facility.

If you are reading this, perhaps you already know why it makes sense in your
case
. If you are just curious, as makers of open source tools for
Kubernetes application packaging and server access management, here is what we have heard from users
of our software:

  • It can be dramatically cheaper, especially for predictable workloads.
  • Regulations: sometimes you have to run software modified for countries it
    runs in (or even in certain states!)
  • Need to use specialized hardware.
  • Latency: sometimes your software must be deployed 5ms away from the data
    it’s processing and there isn’t an AWS region nearby.
  • The data center belongs to your customer and they want your software to run
    there.

There are myriad other reasons. The colocation market is still growing, after
all, so let’s get the question “why” out of the way and focus on “how”.

Rolling your own servers can be a daunting proposition, especially for younger
technologists who are used to bootstrapping formidable server fleets with an
API key, not with their bare hands covered in a mixture of blood, sweat and a
server rail grease. However, it can be done with sizable cost, performance and
compliance benefits – and Kubernetes (aka, K8s) can be your secret weapon!

server racks

“… Sometimes I feel nobody gives me no warning
Find my head is always up in the clouds in a dream world
It’s not easy, living on my own…”
Freddie Mercury

Why Kubernetes?

We can all agree that our industry is prone to hype and sometimes we feel the
pressure of adopting a new technology simply because our peers and competitors
do. Before diving into challenges of adopting Kubernetes, let’s remind
ourselves of why someone should (or should not) bother.

The primary benefit of K8s is to increase infrastructure utilization through
the efficient sharing of computing resources across multiple processes. As your
organization adopts more workloads of varying performance envelopes, the art of
bin packing hundreds of micro-services
across available computing resources becomes more and more critical. Kubernetes
is the master of dynamically allocating computing resources to fill the demand.
This allows users to define infrastructure requirements for their applications
using code, and shortens the time to production significantly relative to
trying to manually “bin pack” your micro-services into a static hardware cabinet.

In other words, in addition to dynamic resource scheduling, Kubernetes allows
users to realize many of the cloud benefits while running on bare metal servers
.

Should you roll your own servers?

If you are not certain, the answer is most likely “no”. The staggering
growth of AWS happened for a reason. Software-defined and globally distributed
infrastructure which allows users to pay only for the resources they are using
on a per-second basis is incredible. (If you are a typical SaaS provider that
is entertaining the idea of managing your own servers, Gitlab’s exploration
into going off the cloud
is a good overview of how they came to the
determination it was not the right choice for them.)

This post is for those who either don’t have the luxury of using a cloud
provider or who have reached the conclusion that the benefits of colo outweigh
the costs of using a cloud provider.

The number one piece of advice is to hire someone who has done this before. If
you do that you probably (hopefully) don’t need this blog post. However, this
post may help you hire that person or may help you evaluate what’s involved.

As mentioned above, a reason for expanding beyond public clouds includes wanting a better cost/performance ratio that can be realized by having complete
control over the infrastructure tuning.

One example of such tuning can be the need to run a large amount of mostly idle
instances of a cloud application, perhaps as POCs for customers or sales demos.
A physical server with 20 real cores can run a hundred VMs with their own
virtual vCPUs
(and you can over-provision RAM too!)

This is a blog post, not a book, so let’s keep it focused and make a few assumptions about our mini-datacenter to limit the scope:

  • A single server rack with up to 42 physical servers.
  • Located in a single data center.
  • We’ll use a simple network without hardware redundancy (more about this later).

Colocation and Hardware

If you are rolling your own hardware, you need a place to put your machines. You generally don’t want them next to you unless you have really good noise-cancelling headphones and/or you need a strong heater. Companies who rent “pieces of data centers” are called colocation facilities and the “pieces” they rent are called server cabinets (or
racks). Cabinets usually have individual locks, but if additional physical
security is required, you may request a “cage” i.e. a separate room with its
own lock which will host all of your server cabinets.

There are several form factors for server cabinets to be aware of. It is easier
to get started with a standard 19-inch cabinet
and your local colo facility will likely have that to offer. If you are
going to become a datacenter nerd, you will eventually discover the
OpenCompute project (OCP), which have different dimensions.
That’s a sexy subject on its own and it probably deserves a separate blog post.

A rack is divided into logical units of vertical space called a “U”. Most data
center racks have a height of 42Us. This means they can hold up to 42 of 1U
servers. However, you’ll probably need some Us for the network gear as well.

There are many factors to consider when picking server hardware. Due to the
recent price drops for flash memory and the resurgence of AMD as a viable
competitor to Intel, we now have access to incredible performance concentrated
in a small amount of space. Here’s an example of a system you can have:

  • 2 CPUs of up to 32 cores each.
  • Up to 2TB of error-correcting ECC RAM running at 2666Mhz.
  • 4+ NVMe SSDs and 8 or more SATA SSDs.
  • At least 2 10G network cards.

Even for our limited deployment, we can easily provision over a thousand
physical CPU cores and 40+ terabytes of RAM in a single cabinet! Efficiently
managing this amount of processing power is impossible by hand. That is where
private cloud software, or Kubernetes in our case, comes in handy.

The hardware above is quite vanilla. But as we mentioned above, some companies
use colocation to take advantage of specialized hardware such as FPGAs, GPUs or
even consumer-grade CPUs because they offer much higher single thread
performance, often at the expense of not having ECC memory support or limited
I/O throughput.

Redundancy

An important topic probably worth touching on is designing for failure. Which
things need redundancy? Is that achieved in hardware (HW) or in software (SW)?
The trend is generally to move away from achieving HA via HW and instead using
SW. K8s will move containers around if a server fails, so servers don’t need HW
redundancy (e.g. HA power or HA network interface controllers).

Although, you need to leave sufficient
cluster capacity. Even if each server doesn’t need HA power, you may want to
straddle servers in the cluster and put 12 on circuit A and 12 on circuit B,
provided those have upstream power failure isolation from the colo provider
(this is somewhat of a poor man’s availability zone).

To limit the scope of this article, let’s assume that we do no need separate
availability zones in your setup, but it’s worth mentioning that the level of desired redundancy is an huge factor in the cost!

Now, let’s talk about money.

When you call a colocation company for a price quote, the most common first
question they’ll ask will be: “how much power do you need?” The colo industry
is basically reselling electricity at a premium. Your answer needs to be in
amps (A), where:

A = power (W) / voltage (V)

i.e. a single server consuming 300w will need 2.5 amps at 120 volts. The power
is usually sold on a per-cabinet basis, i.e. if you bought a 15amp cabinet, it
means you can only fit six servers into one. Power is all they care about and
it is not uncommon to receive a fixed-price quote for pre-provisioned
electricity regardless of how much bandwidth you’d consume. A “starter pack”
15amp cabinet with a gigabit connection can be rented for as little as $400 per
month.

The prices will vary, but the number one question you probably have is: “is it
cheaper than AWS?” The only answer I am comfortable saying is “it depends.”
If you already have the skills to manage the infrastructure and your servers
will be well-utilized most of the time, then the DIY route will be
cheaper. But if your workloads are highly variable, you may find
yourself massively over-provisioning and paying for resources that are idle
most of the time. Another major expense of DIY is having to hire a team of SREs to
keep your databases and other infrastructure software running smoothly.

Before concluding that colocation is vastly cheaper, please bear in mind
that AWS also offers unique billing models not available in DIY deployments,
namely spot instances and reserved instances. Spot instances allow you to run
workloads that can tolerate interruption (e.g. non-time sensitive batch
processing jobs) at a significant discount (50-80%). AWS lets you bid a lower
price for EC2 instances and when AWS demand necessitates more capacity, they
reclaim your spot instances with a few minutes notice. Reserved instances are
meant to mimic purchasing your own physical servers which typically have a 3
year life / amortization. You make a commitment to run a particular EC2
instance for 1 or 3 years in exchange for 30-70% discount. Convertible reserved
instances are even more flexible and let you exchange your commitments over
time as you EC2 instance needs change. Just remember that managing reserved instances can be very
difficult and you can actually end up paying more than on-demand rates if you
aren’t careful.

Before leaving AWS strictly because of cost-related concerns, we recommend
checking out vendors who do automated reserved instance management.

Next…

So far, we have covered:

  • Yes, people still (in 2019!) build their own environments in colocation (and
    even leave public clouds like AWS behind). Plenty of our customers do.
  • Kubernetes is a reasonable and much more lightweight alternative to
    virtualization in order to build “cloudy” environments on bare metal servers.
  • The costs can be much lower… or much higher!

In the next chapter, we’ll cover building a bare metal network to run Kubernetes,
among other things.

Stay tuned!


Thanks to Aaron Sullivan and Erik Carlin for reading the draft of this post
and providing valuable suggestions
.

kubernetes

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