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Virtual Machines versus Containers
5:25The contents of Docker containers run directly on top of the host operating system, unlike a virtual machine where they run on top of a guest operating system. Eliminating that guest OS and emulated hardware makes Docker containers much more lightweight than virtual machines.
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In the last stage we took a look at
what Docker is and why people use it.
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In this stage we'll look at how Docker can
streamline your software development in
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a big way.
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Long ago, developers had to install all of
their apps' dependencies on the OS itself
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before they could even
begin development work.
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This may work for your purposes, but
when it comes time to let a team mate or
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customer use your code,
there can be many problems.
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It's not always easy to reproduce what
worked on your machine on their machine.
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Then came virtual machines
which really save the day.
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VMs essentially emulated entire computers
within a developer's computer,
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VMs were great because they allow
developers to install their app's
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dependencies in a virtual machine
keeping it isolated from main OS.
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In certain configurations and for
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certain apps, they can even be faster
than running on native hardware.
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But this isn't the case most of the time.
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Because a virtual machine has
to emulate all the hardware and
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firmware it runs on,
it can be slow to start up.
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And VMs are slower to run
in most circumstances.
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And because the images contain an entire
operating system including packages
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an app may not need, the disk images
are big and impractical to distribute.
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Despite these drawbacks, virtual
machines made it much easier to build
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reproducible environments for apps to
run on, so they exploded in popularity.
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And in 2010, a software project
named Vagrant came along,
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that promised to automate
the creation of VMs.
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Vagrant allowed developers to build
new VMs using a configuration file
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that specified an OS and
software packages to install.
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But Vagrant still suffered from
the inherent problem of virtual machines,
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distributing applications was still
difficult, it wasn't practical to
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pass the VM from developer to developer or
developer to customer.
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Anyone who wanted to
work on Vagrant VM had
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run the initial build to
create their VM from scratch.
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That was the situation when Docker and
the concept of containers arrived in 2013.
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The contents of Docker
containers run directly on
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top of the host operating system.
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Unlike a virtual machine where they run
on top of a guest operating system.
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Eliminating that guest OS and
emulated hardware
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makes Docker containers much more
lightweight than virtual machines.
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A Docker still offers many of the same
benefits of Virtual Machines,
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because they're isolated in a container,
the services running in docker containers
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can't interfere with each other,
or with services on the host.
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Because there's no need for
a full guest OS,
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docker containers offer
many benefits over VMs.
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They start up faster,
because you don't have to wait for
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a whole separate OS to load.
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You can re-use systems
resources more efficiently.
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A virtual machine, usually has to receive
some parts of the host resources and
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can't release them when it's
not actively using them.
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Docker containers can free
resources they are not using.
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Containers can usually take advantage
of the hardware on the host machine and
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ways a VM can.
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For example a VMK usually use the GPU
to run codes but a container is up
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can make full use of it, and
there's less redundancy with containers.
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Whereas VMs usually need the entire
guest OS in order to run successfully,
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containers run strip down versions of
the OS with unnecessary parts removed.
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That means you can run more containers
on the same host than you can with VMs.
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There's one limitation
you should be aware of.
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Depending on the app you're running
a container may not be having faster than
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a virtual machine.
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Containers usually start up
faster than VMs though so
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you'll still see a speed
benefit from switching.
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Docker's architecture has significant
differences from traditional virtual
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machine architecture.
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Docker runs containers on top of light
weight virtualized environments without
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fully virtualized in the home machine.
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Because docker doesn't virtualizing
entire OS, it can run much quicker and
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be far more affordable
than a traditional VM.
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Both virtual machines and containers
run on top of a host operating system.
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To run virtual machines, the host OS
runs software called a hypervisor.
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A hypervisor manages the life cycle of
VMs, starting and stopping them as needed,
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managing their resources and
keeping the whole
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setup secure by isolating the VMs
from the host OS and from each other.
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An entire guest operating system runs
within each virtual machine, and
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your app's dependencies as well as the app
itself are run within the guest OS.
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Contrast this with Docker,
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where containers are run by
the Docker Daemon software.
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Docker containers omit most of
the guest OS except for a few packages.
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Meaning most of the container resources
are devoted to your app's dependencies and
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the app itself.
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Docker doesn't have to run
the entire guest OS to run an app,
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it simply share the host resources
like processors, memory and
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networking devices between each container.
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Even better Docker doesn't exclusively
hold the resources of the host OS.
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When resources are released from a
container other Docker containers can use
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those same resources.
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Rather than entire virtual machines,
it's simpler to think of containers of
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very heavy processes which
the Docker components manage.
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This is what makes Docker a faster and
better way to deploy absent services.
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So that's how Docker containers
differ from virtual machines.
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Up next we'll look at
the details of how Docker works.
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