How to deploy a Homu instance to Heroku

Homu is a CI service that helps you enforce the "never break the build" policy in your GitHub repositories (for more details about Homu check its GitHub repository and homu.io).

homu.io is a Homu instance plus a front-end that lets you easily use Homu with your repositories. However, right now homu.io is not accepting registration of new repositories, though its associated @homu bot is still working non-stop on the repositories that were already registered.

Until homu.io "re-opens" its registration page, you can deploy your own Homu instance on a free Heroku dyno and use it with all your repositories. The rest of this document will tell you how to do that.

WARNING This document doesn't cover how to use Homu or explain Homu terminology like "r+" because that's covered by the homu.io website. Actually, I'm going to cover a little on how Homu works because there's not much documentation on some features. See the operational notes section.

• An extra GitHub account that will become the Homu bot. For example, I'm using @homunkulus. I'll refer to this (i.e. your) account as $HOMU_BOT.
• A Heroku account.

Apologies, I didn't have time to make this procedure shorter/simpler.

The procedure consists of "two" parts: A series of "one-time" steps which you need to do once (obviously), and a series of "per-repository" steps that need to be repeated for each repository you want to use with Homu.

• Deploy the Heroku app that resides in this repository by clicking the button below. Go with the default values for pretty much everything, but feel free to set a name for the Heroku app.

Your Heroku app will crash right after deploying it because we haven't set right values for the credentials -- we'll do that in a bit.

From this point, I'll refer to the name of your Heroku app as $HEROKU_APP.

Homu stores information about open PRs in a SQLite database that is destroyed every night, when Heroku automatically restarts the Homu web dyno. Rebuild the database of PRs automatically by running the sync_all.sh script from this repo once per day, after the dyno has been restarted.

• Set the env var APP_URL to the full URL of your app. For example, "https://homu.herokuapp.com". If you are pushing this commit to an existing Heroku app, you will also need to set HOMU_WEB_SECRET to something like openssl rand -hex 20.
• Visit dashboard.heroku.com and open the Metrics tab to find out what time Heroku restarts your dyno each night. It will be a blue dot on the top graph, and will tell you the exact time when you hover over the dot with your mouse.
• Run heroku addons:add scheduler to add the scheduler to your app, then run heroku addons:open scheduler to open the scheduler admin panel.
• Add a new job, and choose a time that is shortly after the scheduled restart of your dyno every night. Set the job's frequency to "Daily", and set the command to bash sync_all.sh.

Login with your $HOMU_BOT account and perform these steps:

• Create an Oauth application with these parameters:
  • Application name: homu
  • Application description: (leave empty)
  • Homepage URL: https://$HEROKU_APP.herokuapp.com
  • Authorization callback URL: https://$HEROKU_APP.herokuapp.com/callback

NOTE the only field that matters is the callback URL, you can fill the other fields with whatever you want.

• Define some config variables in your Heroku App.
  • Go to https://dashboard.heroku.com/apps/$HEROKU_APP/settings
  • Under the "Config variables" section, update these values:
    • GH_OAUTH_ID: Enter the "Client ID" value of the Oauth application you created in the previous step.
    • GH_OAUTH_SECRET: Enter the "Client Secret" of the Oauth application you created in the previous step.

• Create a Personal Token Account with "repo" and "user" scopes enabled. Use this token as the GH_ACCESS_TOKEN config variable of your Heroku app.

Login with your main GitHub account, the one that owns the repositories you want use Homu with, and perform these steps.

• Tell Homu who has r+ rights.

  • Your Heroku app HOMU_REVIEWERS config variable is a space separated list of GitHub users that have r+ rights over all the repositories (see Limitations) Homu is gatekeeping. For example, set it to "moe larry curly", but without the double quotes, if those three users have r+ rights.

• (Optional) Generate a pair of SSH keys, associate them with GitHub and give Homu your private key. This lets Homu use git locally which speeds up Travis by reducing temporary commits.

  • Generate a pair of SSH keys with e.g. ssh-keygen -t rsa -b 4096 -C "for homu".
  • Associate the public key with your GitHub account.
  • Copy the private key into your Heroku app GIT_SSH_KEY config variable.

For each repository you want to use with Homu, perform these steps. I'll use the $OWNER/$REPO "slug" to refer to a repository that has URL: https://github.com/$OWNER/$REPO.

• Append this repository to the list of repositories Homu is watching.

Currently, homu keeps two list of repos. Each list is stored as a config variable whose format is a space-separated list of repo slugs e.g. "japaric/homu-on-heroku rust-lang/rust". The config var HOMU_TRAVIS_REPOS lists the repos that must always pass Travis CI and HOMU_APPVEYOR_REPOS lists the repos that must always pass AppVeyor CI. If a repository must pass both AppVeyor and Travis then it must appear in both lists.

After updating these variables, your Heroku app should get to the point where it doesn't crash and it should render its dashboard. Head to https://$HEROKU_APP.herokuapp.com to confirm.

• Go to https://github.com/$OWNER/$REPO/settings/collaboration and add $HOMU_BOT as a collaborator.

• Add a webhook to your repository: Go to https://github.com/$OWNER/$REPO/settings/hooks/new and fill the fields with:

  • Payload URL: https://$HEROKU_APP.herokuapp.com/github
  • Content type: application/json
  • Secret: (the value of your Heroku app GH_WEBHOOK_SECRET config variable)
  • Events: (pick 'let me select individual events' and choose Issue comment, Pull request, Push and Status)

After you create the webhook, GitHub will send a test payload to test your service. This test should succeed at this point. If not check your Heroku app logs for clues about what went wrong.

• Append these two key-value pairs to your repository .travis.yml:

branches:
    only:
        # Only needed if you are already using branches.only.
        - auto

notifications:
    webhooks: https://$HEROKU_APP.herokuapp.com/travis

If you are going to use the "try" feature you'll also need to add the try branch to the branches.only list. Again, this is only necessary if you are already using the branches.only list.

That's it! Homu is now gatekeeping this repository. You should now be able to r+ pull requests.

The Heroku app in its current form has a few limitations, but depending on your use case these may not matter to you. The limitations are listed below:

• We use the same set of reviewers for all the repos.

Both issues can be fixed with config variables that override the "global" values on a per repository basis. We just have to settle on a format for the variable name. Strawman format:

# Global values
HOMU_REVIEWERS="larry moe curly"

# Overrides
HOMU_REVIEWERS_FOR_${OWNER//-/_}_${REPO//-/_}="larry moe"

# NOTE ${VAR//-/_} means $VAR but with the `-` replaced with `_`. Example: if VAR=the-three-stooges,
# then ${VAR//-/_} is "the_three_stooges"

In the future, I might update the Heroku app in this repository and you may want to update your deployed Heroku app to use a new release. You can do that with the following commands:

NOTE To run these commands, you'll need to have the Heroku toolbelt installed. Alternatively, you can use this Docker image that comes with a pre-installed Heroku toolbelt.

$ heroku login
$ git clone https://github.com/japaric/homu-on-heroku
$ cd homu-on-heroku
$ git remote add heroku https://git.heroku.com/$HEROKU_APP.git
$ git push heroku master

When you configure your repository to work with Homu for the first time, Homu doesn't know about the existing PRs opened against your repo -- that's why the Homu queue for your repository is empty. The synchronize button makes Homu go through your opened PRs and adds them to the queue.

WARNING The synchronize button on queue/all is known to not work. You'll get an internal server error.

NOTE You don't need to click the synchronize button to make Homu learn about new PRs because Homu will do that automatically.

Another scenario where you might need to use it is when new PRs are sent against your repo while Homu was sleeping (if you are running it on a free dyno).

Homu only listen to commands on PRs that appear on your repository queue. If your PR doesn't appear on the queue you probably need to use the synchronize button.

This might happen if Homu was sleeping when the Travis test finished. The PR will appear as "pending" in queue even though the Travis build finished. One way to unstuck Homu is to push a new commit to the PR or force push an amendment to the HEAD commit without any change.

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)

at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.