Docker Application Packages

An experimental utility to help make Compose files more reusable and sharable.

The problem application packages solve

Compose files do a great job of describing a set of related services. Not only are Compose files easy to write, they are generally easy to read as well. However, a couple of problems often emerge:

1. You have several environments where you want to deploy the application, with small configuration differences
2. You have lots of similar applications

Fundamentally, Compose files are not easy to share between concerns. Docker Application Packages aim to solve these problems and make Compose more useful for development and production.

Looking at an example

Let's take the following Compose file. It launches an HTTP server which prints the specified text when hit on the configured port.

version: '3.2'
services:
  hello:
    image: hashicorp/http-echo
    command: ["-text", "hello world"]
    ports:
      - 5678:5678

With docker-app installed let's create an Application Package based on this Compose file:

$ docker-app init --single-file hello
$ ls
docker-compose.yml
hello.dockerapp

We created a new file hello.dockerapp that contains three YAML documents:

• metadatas
• the Compose file
• settings for your application

It should look like this:

version: 0.1.0
name: hello
description: ""
namespace: ""
maintainers:
- name: yourusername
  email: ""
targets:
  swarm: true
  kubernetes: true

--
version: '3.2'
services:
  hello:
    image: hashicorp/http-echo
    command: ["-text", "hello world"]
    ports:
      - 5678:5678

--
{}

Let's edit the settings section and add the following default values for our application:

port: 5678
text: hello development
version: latest

Then modify the Compose file section in hello.dockerapp, adding in the variables.

version: '3.2'
services:
  hello:
    image: hashicorp/http-echo:${version}
    command: ["-text", "${text}"]
    ports:
      - ${port}:5678

Finally you can test everything is working, by rendering the Compose file with the provided default values.

$ docker-app render
version: "3.2"
services:
  hello:
    command:
    - -text
    - hello development
    image: hashicorp/http-echo:latest
    ports:
    - mode: ingress
      target: 5678
      published: 5678
      protocol: tcp

You can then use that Compose file like any other. You could save it to disk or pipe it straight to docker stack or docker-compose to launch the application.

$ docker-app render | docker-compose -f - up

This is where it gets interesting. We can override those settings at runtime, using the --set option. Let's specify different option and run render again:

$ docker-app render --set version=0.2.3 --set port=4567 --set text="hello production"
version: "3.2"
services:
  hello:
    command:
    - -text
    - hello production
    image: hashicorp/http-echo:0.2.3
    ports:
    - mode: ingress
      target: 5678
      published: 4567
      protocol: tcp

If you prefer you can create a standalone configuration file to store those settings. Let's create prod.yml with the following contents:

version: 0.2.3
text: hello production
port: 4567

You can then run using that configuration file like so:

$ docker-app render -f prod.yml

More examples are available in the examples directory.

Installation

Pre-built binaries are available on GitHub releases for Windows, Linux and macOS.

wget https://github.com/docker/app/releases/download/v0.2.0/docker-app-linux.tar.gz
tar xf docker-app-linux.tar.gz
cp docker-app-linux /usr/local/bin/docker-app

Integrating with Helm

docker-app comes with a few other helpful commands as well, in particular the ability to create Helm Charts from your Docker Applications. This can be useful if you're adopting Kubernetes, and standardising on Helm to manage the lifecycle of your application components, but want to maintain the simplicity of Compose when writing you applications. This also makes it easy to run the same applications locally just using Docker, if you don't want to be running a full Kubernetes cluster.

$ docker-app helm

This will create a folder, <my-application-name>.chart, in the current directory. The folder contains the required Chart.yaml file and templates describing the stack Kubernetes object based on the Compose file in your application.

Note that this requires the Compose Kubernetes controller available in Docker for Windows and Docker for Mac, and in Docker Enterprise Edition.

Single file or directory representation

If you prefer having the three documents in separate YAML files, omit the -s option to the docker-app init command. This will create a directory instead of a singe file, containing metadata.yml, docker-compose.yml and settings.yml.

Sharing your application on the Hub

You can push any application to the Hub using docker-app push:

$ docker-app push --namespace myHubUser --tag latest

This command will create an image named myHubUser/hello.dockerapp:latest on your local Docker daemon, and push it to the Hub.

By default, this command uses the application version defined in metadata.yml as the tag, and the value of the metadata field namespace as the image namespace.

All docker-app commands accept a local image name as input, which means you can run on a different host:

$ docker pull myHubUser/hello.dockerapp:latest
$ docker-app inspect myHubUser/hello

Next steps

We have lots of ideas for making Compose-based applications easier to share and reuse, and making applications a first-class part of the Docker toolchain. Please let us know what you think about this initial release and about any of the ideas below:

• Introducing environments to the settings file
• Docker images which launch the application when run
• Built-in commands for running applications
• Saving required images into the application artifact to support offline installation
• Automatically validating Compose files against the schema for the specified version
• Signing applications with notary

Usage

$ docker-app
Docker App Packages

Usage:
  docker-app [command]

Available Commands:
  helm        Render the Compose file for this app as an Helm package
  help        Help about any command
  init        Initialize an app package in the current working directory
  inspect     Retrieve metadata for a given app package
  render      Render the Compose file for this app
  version     Print version information

Flags:
  -h, --help   help for docker-app

Use "docker-app [command] --help" for more information about a command.