Docker Compose in Greengrass

This repository is an example layout for building multiple Docker images and Greengrass components, where each component can contain a docker-compose file for referencing public Docker images or privately-hosted Docker images.

Project Structure

This project contains the following:

1. components directory - each subdirectory in this directory contains the source code for a Greengrass component. The subdirectory name matches the component name.
2. docker directory - each subdirectory in this directory contains the source code for a Docker image. The subdirectory name matches the image name.
3. .env file - contains ECR repository variable and any user-defined environment variables for use during the build.
4. build_all.sh file - script to build all Greengrass components and Docker images.
5. publish_all.sh file - script to publish all Greengrass components and Docker images.

Using the Projet

Requirements

• AWS CLI
• GDK
• jq - apt install jq
• docker
• docker-compose

Setup

Greengrass Permission

As per the Greengrass Docker documentation, the Greengrass device role may need extra policies attached for correct function.

To pull images hosted in private ECR repositories, add the following policy:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": [
        "ecr:GetAuthorizationToken",
        "ecr:BatchGetImage",
        "ecr:GetDownloadUrlForLayer"
      ],
      "Resource": [
        "*"
      ],
      "Effect": "Allow"
    }
  ]
}

In addition, to pull components stored in S3 buckets (including the Docker Compose file in this project), add the following policy:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": [
        "s3:GetObject"
      ],
      "Resource": [
        "*"
      ],
      "Effect": "Allow"
    }
  ]
}

Elastic Container Registry

By default, this project pushes an image tagged python-hello-world:latest and expects an ECR repository of the same name to exist. In the AWS console, create a new ECR repository with default options named python-hello-world. View the push commands and copy the base URL for the ECR repository into the .env file, replacing the ECR_REPO variable. For example:

ECR_REPO=012345678901.dkr.ecr.us-west-2.amazonaws.com

Note that the python-hello-world:latest has been stripped off to get the base URL.

A new ECR repository will be required for each Docker image pushed.

Build

To build all components and images at once, run ./build_all.sh. To build an individual component/image, change to its directory and run source ../../.env && ./build.sh.

Publish

To publish all components at once, run ./publish_all.sh.

To publish an individual Docker image, change to that image's directory and run source ../../.env && ./publish.sh. To publish an individual Greengrass component, change to that component's directory and run gdk component publish.

Deploy

From the AWS Console, select a deployment for a healthy Greengrass core device and deploy the latest version of the com.docker.PythonHelloWorld component. On the local device, the logs will show that the component successfully sent and received a number of messages. Alternatively, the Debug Console can be used to view the messages being published and received live. However, the component starts up, publishes its messages, then stops; if no messages are appearing, ensure to run the component again.