#Grim: Dead simple build server

Grim is the "GitHub Responder In MediaMath". We liked the acronym and awkwardly filled in the details to fit it. In short, it is a task runner that is triggered by GitHub push/pull request hooks that is intended as a much simpler and easy-to-use build server than the more modular alternatives (eg. Jenkins).

On start up, Grim will:

1. Create (or reuse) an Amazon SQS queue with the name specified in its config file as GrimQueueName
2. Detect which GitHub repositories it is configured to work with
3. Create (or reuse) an Amazon SNS topic for each repository
4. Configure each created topic to push to the Grim queue
5. Configure each repositories' AmazonSNS service to push hook updates (push, pull_request) to the topic

An example including two repositories watched by three Grimd's (one in EC2 and two MacBookPros).

Each GitHub repo can push to exactly one SNS topic. Multiple SQS queues can subscribe to one topic and multiple Grim instances can read from the same SQS queue. If a Grim instance isn't configured to respond to the repo specified in the hook it silently ignores the event.

##Installation

1. Get grimd

wget https://artifactory.mediamath.com/artifactory/libs-release-global/com/mediamath/grim/grimd/[RELEASE]/grimd-[RELEASE].zip

2. Global Configuration

Grim tries to honor the conventional Unix filesystem hierarchy as much as possible. Configuration files are by default found in /etc/grim. You may override that default by specifying --config-root [some dir], more briefly -c [some dir] or by setting the GRIM_CONFIG_ROOT environment variable. Inside that directory there is expected to be a config.json that specifies the other paths used as well as global defaults. Here is an example:

{
	"GrimQueueName": "grim-queue",
	"ResultRoot": "/var/log/grim",
	"WorkspaceRoot": "/var/tmp/grim",
	"AWSRegion": "us-east-1",
	"AWSKey": "xxxx",
	"AWSSecret": "xxxx",
	"GitHubToken": "xxxx",
	"HipChatToken": "xxxx"
}

If you don't configure GrimQueueName, ResultRoot or WorkspaceRoot Grim will use default values. The AWS credentials supplied must be able to create and modify SNS topics and SQS queues.

Required GitHub token scopes

• write:repo_hook to be able to create/edit repository hooks
• repo:status to be able set commit statuses
• repo to be able to download the repo

3. Repository Configuration

In order for Grim to respond to GitHub events it needs subdirectories to be made in the configuration root. Inside those subdirectories should be a config.json and optionally a build.sh. Here is an example directory structure:

/etc/grim
/etc/grim/config.json
/etc/grim/MediaMath
/etc/grim/MediaMath/grim
/etc/grim/MediaMath/grim/config.json
/etc/grim/MediaMath/grim/build.sh

The file config.json can have an empty JSON object or have the following fields:

{
	"GitHubToken": "xxxx",
	"HipChatToken": "xxxx"
	"HipChatRoom": "xxxx",
	"PathToCloneIn": "/go/src/github.com/MediaMath/grim"
}

The GitHub and HipChat tokens will override the global ones if present. The HipChat room is optional and if present will indicate that status messages will go to that room. The field PathToCloneIn is relative to the workspace that was created for this build.

Build script location

Grim will look for a build script first in the configuration directory for the repo as build.sh and failing that in the root of the cloned repo as either .grim_build.sh or grim_build.sh.

The environment variables available to this script are documented here.

Environment Variables

CLONE_PATH= the path relative to the workspace the repo is cloned in 
GH_EVENT_NAME= either 'push', 'pull_request' or '' (for manual builds)
GH_ACTION= the sub action of a pull request (eg. 'opened', 'closed', or 'reopened', 'synchronize') or blank for other event types
GH_USER_NAME= the user initiating the event
GH_OWNER= the owner part of a repo (eg. 'MediaMath')
GH_REPO= the name of a repo (eg. 'grim')
GH_TARGET= the branch that a commit was merged to
GH_REF= the ref to build
GH_STATUS_REF= the ref to set the status of
GH_URL= the GitHub URL to find the changes at