When comparing Docker vs Puppet, the Slant community recommends Docker for most people. In the question“What are the best WordPress deployment tools?” Docker is ranked 4th while Puppet is ranked 5th. The most important reason people chose Docker is:
Docker creates a single object, containing an application with its dependencies, that can be moved between any docker-enabled machines, guaranteeing the same environment for application execution.
Specs
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Pros
Pro Allows for portable application deployment
Docker creates a single object, containing an application with its dependencies, that can be moved between any docker-enabled machines, guaranteeing the same environment for application execution.
Pro Git-like capabilities
Docker tracks changes in systems. It allows for commits and rollbacks and for quick deployment due to having to deploy only the updated code.
Pro Allows re-using components
Docker essentially allows creating boilerplate systems (a LAMP stack, for example) that can be used as a starting point on multiple projects. And you can find multiple such containers already created by people in their public registry.
Pro Automatic build
Allows automatically assembling a container from its source code.
Pro Provides easy sharing and installation of containers through a public registry
Docker allows easily pushing and pulling containers to and from their public index.docker.io registry. Additionally, dotCloud maintains a list of official repositories of the more popular containers.
Pro Application-centric
Pro Works in virtualized environments
You can set up Docker within an already virtualized environment such as a virtual machine. This allows you to run Docker on Mac and Windows, among other use-cases.
Pro Low overhead
Pro Supports a wide range of isolation tools
Docker can be used with OpenVZ, systemd-nspawn, libvirt-lxc, libvirt-sandbox, qemu/kvm, BSD Jails, Solaris Zones, and chroot.
Pro Tool ecosystem

Pro Declarative sematic
You define the state the server should be in and Puppet transforms it that state. This is opposed to explicitly declaring a list of actions to be performed.
If a developer wants more flexibility and control there's always the option of falling back to explicitly running commands but that's discouraged.
Pro Broad cross-platform support
Puppet is supported on a wide range of operating systems. See the Docs for a complete list.
Pro Large helpful community
Puppet is very mature and relatively old. This means that it has gathered quite a following over the years. This large community means that there are a lot of modules, guides and configuration recipes ready to use built by the community.
Pro Complete
Puppet is a complete solution in terms of available features and modules. It has full support for all the main Operating Systems and provides lots of tools for its users.
Pro Exceptional enterprise support
Puppet Enterprise is used by 75 of the fortune 100 companies.
Pro All-in-one Package since version 4
With Facter, Collective and Hiera.
Pro Helpful UI
Puppet's UI is very useful. It allows real-time control of managed nodes by using modules and configuration recipes that are on the master servers. Although the UI is great for management, it lacks when trying to configure modules.
Pro Easy to learn
Puppet is model-driven and easier for diverse teams (that may include non-devs) to learn than it's main competitor, Chef.
Pro Can enforce policy even without a connection to the puppet master
With cached catalogs, puppet agents can continue to enforce policy even while your masters aren't functional
Cons
Con Large image size
Con Security concerns
Con Kernel OS fragmentation
Con Poor training materials
The puppet documentation does not contain any proper tutorials to help new users on board easily.
Con Interaction between modules can get quite complex very fast
Due to it's out of order execution you can easily get into race condition between different modules. You have to be very careful declaring pre-requisites for the tasks so they don't step on top of each other. On the other hand when you get this lets you deploy things much faster than straight line execution tools
Con Lacks flexibility
The lack of control over Puppet's model-driven approach can result in less flexibility and power from the tool.
Con Solid knowledge of Ruby is needed to create your own modules
Modules and configurations are written in a specific language based on Ruby or in Ruby itself. So in order to be able to create custom configuration and modules you need a solid knowledge of Ruby.
Although it's fair to mention that there are many modules already available for every use-case.
Con Requires culture shifts
You might find difficulty adopting puppet due to the effort involved in convincing admins to switch from procedural automation to desired state automation.
Con Does not enforce policy when the puppetmaster is offline
Does not enforce policy when the puppetmaster is offline, does have a caching mechanism but since it does not include any files that need to be transfer it basically does not work
Con Slow as hell
Compared with other CM tools it's very slow and needs to do a lot of caching to give it the impression that it's fast (which it's not)
Con Syntax is a mess
To use puppet to the full extent you need to know the following tools; most of them are an integral part of puppet, Ruby, Ruby templates, puppet DSL, Hiera, Facter and Mcollective which all have a different syntax
