With Packer installed, it is time to build your first image. For speed, simplicity's sake, and because it's free to download, you will build a Docker container. You can download Docker here if you don't have it installed.
A Packer template is a configuration file that defines the image you want to build and how to build it. Packer templates use the Hashicorp Configuration Language (HCL).
Create a new directory named packer_tutorial. This directory will contain your Packer template for this tutorial.
Navigate into the directory.
Create a file docker-ubuntu.pkr.hcl.
$ touch docker-ubuntu.pkr.hcl
Add the following HCL block to it and save the file.
packer {
required_plugins {
docker = {
version = ">= 1.0.8"
source = "github.com/hashicorp/docker"
}
}
}
source "docker" "ubuntu" {
image = "ubuntu:jammy"
commit = true
}
build {
name = "learn-packer"
sources = [
"source.docker.ubuntu"
]
}
This is a complete Packer template that you will use to build an Ubuntu Docker image. In the following sections, you will review each block of this template in more detail.
Packer BlockThe packer {} block contains Packer settings, including specifying a required Packer version.
In addition, you will find required_plugins block in the Packer block, which specifies all the plugins required by the template to build your image. Even though Packer is packaged into a single binary, it depends on plugins for much of its functionality. Some of these plugins, like the Docker Builder which you will to use, are built, maintained, and distributed by HashiCorp — but anyone can write and use plugins.
Each plugin block contains a version and source attribute. Packer will use these attributes to download the appropriate plugin(s).
source attribute is only necessary when requiring a plugin outside the HashiCorp domain. You can find the full list of HashiCorp and community maintained builders plugins in the Packer Builders documentation page.In the example template above, Packer will use the Packer Docker builder plugin that is greater than or equal to version 1.0.8.
The source block configures a specific builder plugin, which is then invoked by a build block. Source blocks use builders and communicators to define what kind of virtualization to use, how to launch the image you want to provision, and how to connect to it. Builders and communicators are bundled together and configured side-by-side in a source block. A source can be reused across multiple builds, and you can use multiple sources in a single build. A builder plugin is a component of Packer that is responsible for creating a machine and turning that machine into an image.
A source block has two important labels: a builder type and a name. These two labels together will allow us to uniquely reference sources later on when we define build runs.
In the example template, the builder type is docker and the name is ubuntu.
source "docker" "ubuntu" {
image = "ubuntu:jammy"
commit = true
}
Each builder has its own unique set of configuration attributes. The Docker builder starts a Docker container, runs provisioners within this container, then exports the container for reuse or commits the image.
In the example template, the Docker builder configuration creates a new Docker image using ubuntu:jammy as the base image, then commits the container to an image.
Tip
The example template does not configure any communicators, because the Docker builder is a special case where Packer can't use a typical ssh or winrm connection. To see an example of configuring a communicator, refer to the AWS EBS example.
The build block defines what Packer should do with the Docker container after it launches.
In the example template, the build block references the Docker image defined by the source block above (source.docker.ubuntu).
build {
name = "learn-packer"
sources = [
"source.docker.ubuntu"
]
}
Tip
In later tutorials, you will add the provision block (define additional provisioning steps) and post-process block (define what do to with the build artifacts) to the build block.
Initialize your Packer configuration.
Packer will download the plugin you've defined above. In this case, Packer will download the Packer Docker plugin that is greater than or equal to version 1.0.8.
You can run packer init as many times as you'd like. If you have already have the plugins you need, Packer will exit without an output.
Packer has now downloaded and installed the Docker plugin. It is ready to build the Docker image!
We recommend using consistent formatting in all of your template files. The packer fmt command updates templates in the current directory for readability and consistency.
Format your template. Packer will print out the names of the files it modified, if any. In this case, your template file was already formatted correctly, so Packer won't return any file names.
You can also make sure your configuration is syntactically valid and internally consistent by using the packer validate command.
Validate your template. If Packer detects any invalid configuration, Packer will print out the file name, the error type and line number of the invalid configuration. The example configuration provided above is valid, so Packer will return nothing.
Build the image with the packer build command. Packer will print output similar to what is shown below.
$ packer build docker-ubuntu.pkr.hcl
learn-packer.docker.ubuntu: output will be in this color.
==> learn-packer.docker.ubuntu: Creating a temporary directory for sharing data...
==> learn-packer.docker.ubuntu: Pulling Docker image: ubuntu:jammy
learn-packer.docker.ubuntu: jammy: Pulling from library/ubuntu
learn-packer.docker.ubuntu: 4007a89234b4: Pulling fs layer
## ...
learn-packer.docker.ubuntu: Digest: sha256:bb84bbf2ff36d46acaf0bb0c6bcb33dae64cd93cba8652d74c9aaf438fada438
learn-packer.docker.ubuntu: Status: Downloaded newer image for ubuntu:jammy
learn-packer.docker.ubuntu: docker.io/library/ubuntu:jammy
==> learn-packer.docker.ubuntu: Starting docker container...
learn-packer.docker.ubuntu: Run command: docker run -v /Users/youruser/.packer.d/tmp819964324:/packer-files -d -i -t --entrypoint=/bin/sh -- ubuntu:jammy
learn-packer.docker.ubuntu: Container ID: 6e18a8066f5f9b758a35a257bb7a08a2e06b5b257d51d3599f15466ccab74691
==> learn-packer.docker.ubuntu: Using docker communicator to connect: 172.17.0.2
==> learn-packer.docker.ubuntu: Committing the container
learn-packer.docker.ubuntu: Image ID: sha256:13d5a06b9ad37668669ecef6b8ddcaa81c0e6bcacc140f6e954268e8181ad140
==> learn-packer.docker.ubuntu: Killing the container: 6e18a8066f5f9b758a35a257bb7a08a2e06b5b257d51d3599f15466ccab74691
Build 'learn-packer.docker.ubuntu' finished after 32 seconds 28 milliseconds.
==> Wait completed after 32 seconds 29 milliseconds
==> Builds finished. The artifacts of successful builds are:
--> learn-packer.docker.ubuntu: Imported Docker image: sha256:13d5a06b9ad37668669ecef6b8ddcaa81c0e6bcacc140f6e954268e8181ad140
List all the Docker images to confirm that Packer successfully built your Docker image.
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
<none> <none> 13d5a06b9ad3 About a minute ago 134MB
Congratulations — you built your first image using Packer!
Packer only builds images. It does not attempt to manage them in any way. After they're built, it is up to you to launch or destroy them as you see fit.
You can delete your Docker image by running the following command. Replace IMAGE_ID with the image ID return by the Packer output.
In this tutorial, you launched a Docker container and saved it as an image. Although you essentially repackaged an existing image, you should now have a general idea of how Packer works, what templates are and how to validate and build templates into machine images. Now that you have create your first Packer image, continue to the next tutorial to install and configure software into your image with provisioners.
Refer to the following resources for additional details on the concepts covered in this tutorial:
packer init and packer build commands.RetroSearch is an open source project built by @garambo | Open a GitHub Issue
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