This repository contains the packer configuration for creating the worker AMI from scratch. (The worker AMI is the image that runs the Docker container that runs the student submission.)

The packer-worker.json file contains the configuration for the AMI, including choosing the base image (currently Ubuntu 18.04) and specifying which script to run to set up the AMI. In this case, that script is setup.sh, which does a few things:

1. Install packages.
2. Install Docker and pull the latest Docker image.
3. Save the GitHub key in the image so we can easily clone student work.
4. Install the Autolab autodriver from the Tango repository.

Continuous deployment is set up for this repository on TravisCI. If you have been added to the GitHub organization and you navigate to https://travis-ci.com, you will see the build history for this repository. TravisCI initiates a build for this image each time you commit and push this repository to GitHub.

TravisCI needs to access our AWS_ACCESS_KEY, our AWS_SECRET_KEY, a private GitHub key for the user cmu-15-411-bot, our DOCKER_USERNAME, and our DOCKER_PASSWORD. To do this, we use encryption. Currently, these values are stored in the .travis.yml file. Travis CI generates a key-pair for each repository, so if you change this repository's name or want to change the stored credentials, you will have to run some commands. In particular, you can run travis encrypt AWS_ACCESS_KEY=... AWS_SECRET_KEY=... DOCKER_USERNAME=... DOCKER_PASSWORD=... --add (with the ellipses replaced by the value correponding to that key) to add the encrypted secret keys to the .travis.yml file. (The GitHub key, in contrast, is stored in the encrypted .enc file and decrypted in the .travis.yml file. To encrypt a different key, use travis encrypt-file FILENAME --add.)

The worker will be named in the format "15411_worker_TIMESTAMP.img", where TIMESTAMP is replaced with a TIMESTAMP of when the repo was built.

The worker-docker repository, when pushed, will trigger a build on DockerHub for the cmu411/autograder repository. When this build completes, DockerHub sends a POST request (as specified by the webhook for the autograder repository) to the Heroku app for the docker-to-aws-cd repository. This webapp initiates a build for THIS repository, worker-aws. This will mean that the latest Docker image will be cached on the latest version of the image built from this repository; this avoids re-pulling the latest Docker image when a new worker instance starts up.

Manually building the AMI can be done with the following command:

AWS_ACCESS_KEY=... \
  AWS_SECRET_KEY=... \
  DOCKER_USERNAME=... \
  DOCKER_PASSWORD=... \
  packer build packer-worker.json

You should replace the ellipses ... in each case with the appropriate secret values. Note that this command will actually create the image in the AWS organization. You will also have to have a decrypted SSH key for the cmu-15-411-bot GitHub user in the file cmu-15-411-bot-key.