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# HTSQL in the Cloud

Table of Contents

- Installing at Heroku

These instructions outline how to use HTSQL using a cloud provider where you have a limited application environment.

## Installing at Heroku

Here we describe how to install HTSQL as a Heroku process using their cedar stack.

### Prerequisites

There are some basic steps that you must do if you’re not already using Heroku service. Heroku’s server management tools are written in Ruby and use Git.

1. Install Ruby, Ruby Gems and Git for your platform.
2. Signup for a Heroku Account.
3. Install Heroku CLI command and register your ssh key using `heroku keys:add`.
4. When you first run a `heroku` command, it will prompt for your account information and cache it at `~/.heroku/credentials`.

If you follow Heroku’s quickstart don’t follow the remaining instructions past the Prerequisites since this is intended for ruby application developers.

### Application Template

Next is an application template that matches with Heroku needs. You’ll need to create an empty “project” directory with the following files & content.

`requirements.txt`:

    HTSQL
    PyYAML
    psycopg2

`Procfile`:

    web: python run_htsql.py

`config.yaml`:

    # shell plugin as a default command
    tweak.shell.default:

`run_htsql.py`:

    # create HTSQL application
    import os, yaml
    from htsql import HTSQL
    config = yaml.load(open("config.yaml").read())
    dburi = os.environ['DATABASE_URL'].replace('postgres','pgsql')
    app = HTSQL(dburi, config)

    # start webserver
    from wsgiref.simple_server import make_server
    port = int(os.environ['PORT'])
    srv = make_server('0.0.0.0', port, app)
    srv.serve_forever()

These files can be found in the `demo/heroku` portion of the HTSQL distribution.

### Deployment

Once those files are created, deployment to Heroku’s system is done by first creating a local git repository for your project:

    $ git init
    $ git add .
    $ git commit -m init

Then, initializing the heroku stack:

    $ heroku create --stack cedar

At this point, a PostgreSQL database is needed. For testing, you could use a shared database:

    $ heroku addons:add shared-database

Then, you’re ready to push HTSQL to Heroku:

    $ git push heroku master

You could now go to the URL of the hosted service and enter `/'Hello World'` for a very basic test. If HTSQL server is not up and running, look at the logs:

    $ heroku logs

Likely you will want to customize your deployment, say running it along side your web application and using `nginx` to dispatch requests to some prefix to this process.

### Limitations

One major limitation of Heroku deployment is that Ruby on Rails applications typically do not define foreign keys. Furthermore, the tool Heroku uses to do import and export, taps, discards any foreign key constraints when migrating schemas. Since HTSQL relies upon foreign keys to determine linking, it’s usage is limited to single table queries or manually specified links.

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