keter/README.md

Deployment system for web applications, originally intended for hosting Yesod applications. Keter does the following actions for your application:

• Binds to the main port (usually port 80) and reverse proxies requests to your application based on virtual hostnames.
• Provides SSL support if requested.
• Automatically launches applications, monitors processes, and relaunches any processes which die.
• Provides graceful redeployment support, but launching a second copy of your application, performing a health check, and then switching reverse proxying to the new process.
• Management of log files.

Keter provides many more advanced features and extension points. It allows configuration of static hosts, redirect rules, management of PostgreSQL databases, and more. It supports a simple bundle format for applications which allows for easy management of your web apps.

Quick Start

Do get Keter up-and-running quickly on an Ubuntu system, run:

wget -O - https://raw.github.com/snoyberg/keter/master/setup-keter.sh | bash

(Note: you may need to run the above command twice, if the shell exits after apt-get but before running the rest of its instructions.) This will download and build Keter from source and get it running with a default configuration.

This approach is not recommended for a production system. We do not recommend installing a full GHC toolchain on a production server, nor running such ad-hoc scripts. This is intended to provide a quick way to play with Keter, especially for temporary virtual machines. For a production system, we recommend building the keter binary on a separate system, and tracking it via a package manager or similar strategy.

Bundling your app for Keter

1. Modify your web app to check for the PORT environment variable, and have it listen for incoming HTTP requests on that port. Keter automatically assigns arbitrary ports to each web app it manages. The Yesod scaffold site is already equipped to read the PORT environment variable when it is set.

2. Create a file config/keter.yaml. The minimal file just has two settings:

   exec: ../path/to/executable
   host: mydomainname.example.com
   

   See the bundles section below for more available settings.

3. Create a gzipped tarball with the config/keter.yaml file, your executable, and any other static resources you would like available to your application. This file should be given a .keter file extension, e.g. myapp.keter.

4. Copy the .keter file to /opt/keter/incoming. Keter will monitor this directory for file updates, and automatically redeploy new versions of your bundle.

Setup

Instructions are for an Ubuntu system. Eventually, I hope to provide a PPA for this (please contact me if you would like to assist with this). For now, the following steps should be sufficient:

First, install PostgreSQL

sudo apt-get install postgresql

Second, build the keter binary and place it at /opt/keter/bin. To do so, you'll need to install the Haskell Platform, and can then build with cabal. This would look something like:

sudo apt-get install haskell-platform
cabal update
cabal install keter
sudo mkdir -p /opt/keter/bin
sudo cp ~/.cabal/bin/keter /opt/keter/bin

Third, create a Keter config file. You can view a sample at https://github.com/snoyberg/keter/blob/master/etc/keter-config.yaml.

Fourth, set up an Upstart job to start keter when your system boots.

# /etc/init/keter.conf
start on (net-device-up and local-filesystems and runlevel [2345])
stop on runlevel [016]
respawn

console none

exec /opt/keter/bin/keter /opt/keter/etc/keter-config.yaml

Finally, start the job for the first time:

sudo start keter

Optionally, you may wish to change the owner on the /opt/keter/incoming folder to your user account, so that you can deploy without sudoing.

sudo mkdir -p /opt/keter/incoming
sudo chown $USER /opt/keter/incoming

Bundles

An application needs to be set up as a keter bundle. This is a GZIPed tarball with a .keter filename extension and which has one special file: config/keter.yaml. A sample file is available at https://github.com/snoyberg/keter/blob/master/incoming/foo1_0/config/keter.yaml.

Keter as well supports wildcard subdomains and exceptions, as in this example configuration:

exec: ../com.example.app
args:
    - Hello
    - World
    - 1
host: www.example.com
extra-hosts:
    - "*.example.com"
    - foo.bar.example.com
static-hosts:
    - host: static.example.com
      root: ../static
redirects:
    - from: example.com
      to: www.example.com

Due to YAML parsing, wildcard hostnames will need to be quoted as above. Wildcard hostnames are not recursive, so foo.bar.example.com must be explicitly added as an extra hostname in the above example, or alternatively, *.*.example.com would cover all host names two levels deep. It would not cover host names only one level deep, such as qux.example.com. In this manner, wildcard hostnames correspond to the manner in which SSL certificates are handled per RFC2818. Wildcards may be used in only one level of a hostname, as in foo.*.example.com.

Full RFC2818 compliance is not present - f*.example.com will not be handled as a wildcard with a prefix.

A sample Bash script for producing a Keter bundle is:

#!/bin/bash -ex

cabal build
strip dist/build/yesodweb/yesodweb
rm -rf static/tmp
tar czfv yesodweb.keter dist/build/yesodweb/yesodweb config static

For users of Yesod, The yesod executable provides a keter command for creating the bundle, and the scaffolded site provides a keter.yaml file.

Deploying

In order to deploy, you simply copy the keter bundle to /opt/keter/incoming. To update an app, copy in the new version. The old process will only be terminated after the new process has started answering requests. To stop an application, delete the file from incoming.

PostgreSQL support

Keter ships by default with a PostgreSQL plugin, which will handle management of PostgreSQL databases for your application. To use this, make the following changes:

• Add postgres: true to your config/keter.yaml file.

• Modify your application to get its database connection settings from the following environment variables:

  • PGHOST
  • PGPORT
  • PGUSER
  • PGPASS
  • PGDATABASE

• The Yesod scaffold site is already equipped to read these environment variables when they are set.

Known issues

• There are reports of Keter not working behind an nginx reverse proxy. From the reports, this appears to be a limitation in nginx's implementation, not a problem with Keter. Keter works fine behind other reverse proxies, including Apache and Amazon ELB.

  One possible workaround is to add the following lines to your nginx configuration:

  proxy_set_header Connection "";
  proxy_http_version 1.1;
  

  This has not yet been confirmed to work in production. If you use this, please report either its success or failure back to me.