|
|
@@ -23,15 +23,15 @@ happens, for a few reasons:
|
|
|
|
|
|
* *Size*: VMs are very large which makes them impractical to store and transfer.
|
|
|
* *Performance*: running VMs consumes significant CPU and memory, which makes them impractical in many scenarios, for example local development of multi-tier applications, and
|
|
|
- large-scale deployment of cpu and memory-intensive applications on large numbers of machines.
|
|
|
+ large-scale deployment of cpu and memory-intensive applications on large numbers of machines.
|
|
|
* *Portability*: competing VM environments don't play well with each other. Although conversion tools do exist, they are limited and add even more overhead.
|
|
|
* *Hardware-centric*: VMs were designed with machine operators in mind, not software developers. As a result, they offer very limited tooling for what developers need most:
|
|
|
- building, testing and running their software. For example, VMs offer no facilities for application versioning, monitoring, configuration, logging or service discovery.
|
|
|
+ building, testing and running their software. For example, VMs offer no facilities for application versioning, monitoring, configuration, logging or service discovery.
|
|
|
|
|
|
By contrast, Docker relies on a different sandboxing method known as *containerization*. Unlike traditional virtualization,
|
|
|
containerization takes place at the kernel level. Most modern operating system kernels now support the primitives necessary
|
|
|
for containerization, including Linux with [openvz](http://openvz.org), [vserver](http://linux-vserver.org) and more recently [lxc](http://lxc.sourceforge.net),
|
|
|
- Solaris with [zones](http://docs.oracle.com/cd/E26502_01/html/E29024/preface-1.html#scrolltoc) and FreeBSD with [Jails](http://www.freebsd.org/doc/handbook/jails.html).
|
|
|
+ Solaris with [zones](http://docs.oracle.com/cd/E26502_01/html/E29024/preface-1.html#scrolltoc) and FreeBSD with [Jails](http://www.freebsd.org/doc/handbook/jails.html).
|
|
|
|
|
|
Docker builds on top of these low-level primitives to offer developers a portable format and runtime environment that solves
|
|
|
all 4 problems. Docker containers are small (and their transfer can be optimized with layers), they have basically zero memory and cpu overhead,
|
|
|
@@ -56,17 +56,17 @@ A common problem for developers is the difficulty of managing all their applicat
|
|
|
This is usually difficult for several reasons:
|
|
|
|
|
|
* *Cross-platform dependencies*. Modern applications often depend on a combination of system libraries and binaries, language-specific packages, framework-specific modules,
|
|
|
- internal components developed for another project, etc. These dependencies live in different "worlds" and require different tools - these tools typically don't work
|
|
|
- well with each other, requiring awkward custom integrations.
|
|
|
+ internal components developed for another project, etc. These dependencies live in different "worlds" and require different tools - these tools typically don't work
|
|
|
+ well with each other, requiring awkward custom integrations.
|
|
|
|
|
|
* Conflicting dependencies. Different applications may depend on different versions of the same dependency. Packaging tools handle these situations with various degrees of ease -
|
|
|
- but they all handle them in different and incompatible ways, which again forces the developer to do extra work.
|
|
|
+ but they all handle them in different and incompatible ways, which again forces the developer to do extra work.
|
|
|
|
|
|
- * Custom dependencies. A developer may need to prepare a custom version of his application's dependency. Some packaging systems can handle custom versions of a dependency,
|
|
|
- others can't - and all of them handle it differently.
|
|
|
+ * Custom dependencies. A developer may need to prepare a custom version of their application's dependency. Some packaging systems can handle custom versions of a dependency,
|
|
|
+ others can't - and all of them handle it differently.
|
|
|
|
|
|
|
|
|
-Docker solves dependency hell by giving the developer a simple way to express *all* his application's dependencies in one place,
|
|
|
+Docker solves dependency hell by giving the developer a simple way to express *all* their application's dependencies in one place,
|
|
|
and streamline the process of assembling them. If this makes you think of [XKCD 927](http://xkcd.com/927/), don't worry. Docker doesn't
|
|
|
*replace* your favorite packaging systems. It simply orchestrates their use in a simple and repeatable way. How does it do that? With layers.
|
|
|
|
Alex Gaynor