Docker Cookbook

50 | Chapter 2: Image Creation and Sharing
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warding ports from a Docker container to the host can be done with the regular
Vagrant command:
config
.
vm
.
network
"forwarded_port"
,
guest
:
5000
,
host
:
5000
Overall, it is my opinion that the Docker support in Vagrant should be seen as a tran‐
sitioning step for developers who might have invested a lot of work with Vagrant and
would like to slowly adopt Docker.
Vagrant also features a Docker 
provisioner
. It can be used when
you are starting virtual machines, provisioning them with configu‐
ration management solutions (e.g., Puppet or Chef) but would also
like to start containers within those virtual machines.
See Also
• Vagrant Docker provider 
configuration
• Vagrant Docker provider 
documentation
2.8 Using Packer to Create a Docker Image
Problem
You have developed several configuration management recipes using 
Chef
, 
Puppet
,
Ansible
, or 
SaltStack
. You would like to reuse those recipes to build Docker images.
Solution
Use 
Packer
 from HashiCorp. Packer is a tool to create identical machine images for
multiple platforms from a single template definition. For example, from a template it
can automatically create images for Amazon EC2 (an Amazon Machine Image, or
AMI), VMware, VirtualBox, and DigitalOcean. One of those target platforms is
Docker.
This means that if you define a Packer template, you can automatically generate a
Docker image. You can also post-process it to tag the image and push it to Docker
Hub (see 
Recipe 2.9
).
The following template shows three main steps. First it specifies a 
builder
; here you
use Docker and specify to use the base image 
ubuntu:14.04
. Second, it defines the
provisioning step. Here we use a simple shell provisioning. Finally, it lists post-
processing steps. Here we tag only the resulting image: