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, by 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.
To get Keter up-and-running quickly on an Ubuntu system, run:
wget -O - https://raw.githubusercontent.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. By default Keter will be set up to support HTTPS and
will require you to provide a key and certificate in
/opt/keter/etc. You can
disable HTTPS in
/opt/keter/etc/keter-config.yaml by commenting the certificate
and key lines.
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
keter binary on a separate system, and tracking it via a package manager
or similar strategy.
Bundling your app for Keter
Modify your web app to check for the
PORTenvironment 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
PORTenvironment variable when it is set.
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.
Create a gzipped tarball with the
config/keter.yamlfile, your executable, and any other static resources you would like available to your application. This file should be given a
.keterfile extension, e.g.
/opt/keter/incoming. Keter will monitor this directory for file updates, and automatically redeploy new versions of your bundle.
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
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 ) stop on runlevel  respawn # NB: keter writes logs to /opt/keter/log, but some exceptions occasionally # escape to standard error. This ensures they show up in system logs. console output 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
folder to your user account, so that you can deploy without
sudo mkdir -p /opt/keter/incoming sudo chown $USER /opt/keter/incoming
An application needs to be set up as a keter bundle. This is a GZIPed tarball
.keter filename extension and which has one special file:
config/keter.yaml. A sample file is available at
Keter also 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
*.*.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
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
In order to deploy, you simply copy the keter bundle to
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.
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 the following lines to your
plugins: postgres: true
- Keter can be configured to connect to a remote postgres server using the following syntax:
plugins: postgres: - server: remoteServerNameOrIP port: 1234
Different webapps can be configured to use different servers using the above syntax. It should be noted that keter will prioritize it's own postgres.yaml record for an app. So if moving an existing app from a local postgres server to a remote one (or switching remote servers), the postgres.yaml file will need to be updated manually.
Keter will connect to the remote servers using the
postgres account. This setup
assumes the remote server's
pg_hba.conf file has been configured to allow connections
from the keter-server IP using the
plugins configuration option was added in v1.0 of the
keter configuration syntax. If you are using v0.4 then use
The remote-postgres server syntax was added in v1.4.2.)
Modify your application to get its database connection settings from the following environment variables:
The Yesod scaffold site is already equipped to read these environment variables when they are set.
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.
Additionally, to make sure that nginx does not reset the
Hostheader (which keter uses to choose the right target), you will need to add:
proxy_set_header Host $host;
Keter does not handle password-protected SSL key files well. When provided with such a key file, unlike Apache and Nginx, Keter will not pause to ask for the password. Instead, your https connections will merely stall.
To get around this, you need to create a copy of the key without password and deploy this new key:
openssl rsa -in original.key -out new.key
(Back up the original key first, just in case.)
Stanza-based config files
Starting with Keter 1.0, there is an alternate format for application Keter config files, which allows much more flexibility in defining multiple functionality for a single bundle (e.g., more than one web app, multiple redirects, etc). This README will eventually be updated to reflect all various options. In the meanwhile, please see the following examples of how to use this file format:
Multiple SSL Certificates
Keter is able to serve different certificates for different hosts,
allowing for the deployment of distinct domains using the same
server. An example
keter-config.yaml would look like::
root: .. listeners: - host: "*4" # Listen on all IPv4 hosts port: 80 - host: 127.0.0.1 key: key.pem certificate: certificate1.pem - host: 127.0.0.2 key: key.pem certificate: certificate2.pem
An alternative way to make this possible is adding the following
keter.yaml file in your Yesod app's
config folder as follows:
stanzas: - type: webapp exec: ../yourproject ssl: key: /opt/keter/etc/cert/yourproject.key certificate: /opt/keter/etc/cert/yourproject.crt chain-certificates: 
If you don't have your certificates bundled in one
.crt file, you should add
the other certificates in the following order
ssl: [..] chain-certificates: - /opt/keter/etc/middle.crt - /opt/keter/etc/root.crt
This way you can designate certificates per Yesod App while still having one SSL certificate
in your main
/opt/keter/etc/keter-config.yaml for your other Yesod apps to default to
if they don't have this
ssl: argument in their
NOTE: If you get an error that a Bool was expected instead of an Object when adding the
argument, then for this to work you might need to build Keter from Github, because at the time
of writing the version of Keter on Hackage does not have this functionality. Just clone or
download this repository and build it using stack.
- Keter spawns multiple failing process when run with
sudo start keter.
- This may be due to Keter being unable to find the SSL certificate and key.
Try to run
sudo /opt/keter/bin/keter /opt/keter/etc/keter-config.yaml. If it fails with
keter: etc/certificate.pem: openBinaryFile: does not existor something like it, you may need to provide valid SSL certificates and keys or disable HTTPS, by commenting the key and certificate lines from
- This may be due to Keter being unable to find the SSL certificate and key. Try to run
If you are interested in contributing, see https://github.com/snoyberg/keter/blob/master/incoming/README.md for a complete testing workflow. If you have any questions, you can open an issue in the issue tracker, ask on the #yesod freenode irc channel, or send an email to email@example.com.