The document discusses OpenShift cartridges, which are technology stacks used to offer or customize services on the OpenShift platform. It outlines the history and evolution from cartridge v1.0 to v2.0, detailing the requirements, components, and functionalities necessary for implementing and managing cartridges effectively. Additional resources, quickstart examples, and communication channels for community support are also provided.

1. OpenShift Community Day
Writing Cartridges
Bill DeCoste
Principal Software Engineer
wdecoste@redhat.com
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2. Target Audience
You...
● Wish to offer new user services on an OpenShift PaaS
● Customize an existing user service on a PaaS
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3. What are Cartridges?
● Cartridge – A technology stack or framework (PHP, Perl, Java/JEE,
Ruby, Python, MySQL, etc.) definition
● Plugin – Auth, DNS, etc.
● Gear – Allocation of memory, compute, and storage resources for
running applications. Live on Nodes.
● Application – Instantiation of a Cartridge. Overloaded term, I know.
● Scaled/Scalable Application – Instantiated in multiple Gears
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4. Suggestions ...
● Start with a DIY (More significant for Cart V1)
– Resolve many installation and configuration issues (e.g. bindings,
logging)
● Existing Quickstart or sample?
● Start with a similar cartridge
– Apache based?
– JEE Application Server?
– Embeddable Database?
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5. Requirements
● The OpenShift Cartridge API consists of:
– Executable files
– stdout/stderr
– Environment variables
● You can use any language but we find bash the fastest
– Bash “SDK” provided, other languages planned
● The software you are packaging either needs to be on the system or
included in your cartridge
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6. History – Cartridge V1.0
● Opensource, but not easy to implement or customize
– Overly large number of files/scripts
– Blurred Node vs Cartridge responsibility
(e.g. root access required by Cartridge)
– Each version required a new Cartridge
● Difficult to maintain
– APIs not versioned
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7. History – Cartridge V2.0
● Eased implementation, customization, and
maintenance
– Greatly reduced number of files/scripts
– Well-defined Cartridge vs Node responsibility
(e.g. root access not required by Cartridge)
– Well-defined and versioned API
– Multiple versions supported in single Cartridge
● Documentation:
https://github.com/openshift/origin-server/blob/master/node/README.writing_cartridges.md
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8. Minimal Cartridge
+- bin
| +- setup
| +- control
+- env
+- metadata
| +- manifest.yml
*Assumes packaged software already installed on system
*Most cartridges will have more files
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9. metadata/manifest.yml
● Elements
– Name
– Version
– Cartridge-Version
– Cartridge-Vendor
– Endpoints
*Other elements for defining features of your cartridge and it's packaged
software
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10. Endpoints
● Cartridges must explicitly declare which ports they will bind to, and
provide meaningful variable names to describe:
– The IP address(es) reserved/available for binding
– The Gear-local ports to which the cartridge services will bind
– (Optional) Publicly proxied ports which expose Gear-local ports for
use by the application's users or across application Gears
Endpoints:
- Private-IP-Name: <name of IP variable> (e.g. IP => OPENSHIFT_shortname_IP)
Private-Port-Name: <name of port variable> (e.g. HTTP_PORT)
Private-Port: <port number> (e.g. 8080)
Public-Port-Name: <name of public port variable> (e.g. HTTP_PROXY_PORT)
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11. Hooks (in-flux)
● Cartridges may need to act when some other cartridge is
added/removed from an application.
● This functionality is supported using Publish/Subscribe connectors in
the manifest.yml.
Subscribes:
set-mysql-connection-info: subscribe script
Type: "NET_TCP:db:mysql" subscription key
Publishes:
publish-mysql-connection-info: publish script
Type: "NET_TCP:db:mysql" subscription key
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12. bin/setup
● Responsible for creating and/or configuring the files that were copied
from the cartridge repository into the gear's directory.
● Option --version
– Which version of the packaged software has been called for
– Possible to support n versions of the software, allows reuse of like
code/configuration files etc
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13. bin/control
OpenShift calls control when it wants work from you or your
packaged software
● start – cartridge and the package software (httpd)
● stop – cartridge and the package software (mysqld)
● build – The application developer pushed new code to your
language cartridge for processing (maven)
● deploy – Code compiled but application not yet started. (Update
database)
● Others: threaddump, restart, reload, status
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14. bin/teardown
● Prepares the gear for the cartridge to be removed. This script will not
called when the gear is destroyed.
● The teardown script is only run when a cartridge is to be removed
from the gear.
● The gear is expected to continue to operate minus the functionality of
your cartridge.
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15. Template
● Provides an minimal example of an application written in the
language/framework your cartridge is packaging
– Typically application to web applications (e.g. homepage)
● Action Hooks
– Executables for custom lifecycle
– e.g. pre-build, post-build, pre-deploy, post-deploy
NOTE: Build lifecycle details available in doc
● Markers
– Control cartridge behavior
– e.g. hot_deploy, disable_auto_scaling, force_clean_build, java7
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16. System Environmental Variables (in-flux)
● System Provided (subset)
OPENSHIFT_APP_DNS the application's fully qualified domain name that your cartridge is a part of
OPENSHIFT_APP_NAME the validated user assigned name for the application. Black list is system dependent.
OPENSHIFT_APP_UUID OpenShift assigned UUID for the application
OPENSHIFT_DATA_DIR the directory where your cartridge may store data
OPENSHIFT_GEAR_DNS the gear's fully qualified domain name that your cartridge is a part of. May or may not be equal to OPENSHIFT_APP_DNS
OPENSHIFT_GEAR_NAME OpenShift assigned name for the gear. May or may not be equal to OPENSHIFT_APP_NAME
OPENSHIFT_GEAR_UUID OpenShift assigned UUID for the gear
OPENSHIFT_HOMEDIR OpenShift assigned directory for the gear
OPENSHIFT_REPO_DIR the directory where the developer's application is "archived" to and will be run from.
OPENSHIFT_TMP_DIR the directory where your cartridge may store temporary data
● Cartridge Provided (examples)
OPENSHIFT_MYSQL_DB_HOST
OPENSHIFT_MYSQL_DB_PASSWORD
OPENSHIFT_MYSQL_DB_PORT
OPENSHIFT_MYSQL_DB_USERNAME
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17. Installing a V2 Cartridge
● Typically available as RPMs
● Added to /usr/libexec/openshift/cartridges/v2
● Install Cartridge:
oo-admin-cartridge -a install -s /usr/libexec/openshift/cartridges/v2/XXX
● Clear Cache
From /var/www/openshift/broker, run bundle exec rake tmp:clear OR
Run `script/rails console` and enter 'Rails.cache.clear',
● Confirm
rhc cartridge list
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18. Quickstarts/Samples
● Many, many easy-to-install applications to showcase Cartridge use
● https://github.com/openshift
● Django, Rails, Tomcat, JEE, Mongo, Redmine, CakePHP, IronMQ,
etc.
● Typically follow install pattern:
rhc create app …
cd app
git remote add upstream …
git pull -s recursive -X theirs upstream master
● Add your own!
● NOTE: Quickstarts blend of v1/v2. Not all tested vs V2 yet
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19. Thank You!
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20. Channels
● G+ Community
https://plus.google.com/communities/114361859072744017486
● E-Mail
– OpenShift Users: users@lists.openshift.redhat.com
– Origin Developers: dev@lists.openshift.redhat.com
● IRC: irc.freenode.net
– OpenShift Users: #openshift
– Origin Developers: #openshift-dev
– Node/Cartridge Developers: #openshift-dev-node
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21. Channels
● Forums
http://openshift.redhat.com/community/forums/openshift
● Blogs
https://openshift.redhat.com/community/blogs/
http://mattoncloud.org/
http://www.billdecoste.net
http://www.krishnaraman.net
http://cloud-mechanic.blogspot.com
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22. OpenSource
● GitHub: https://github.com/openshift
– Origin: origin-server
– OSE: enterprise-server
– Community Cartridges: origin-community-cartridges
– Quickstarts, Examples
– Watch, Star, Contribute!!!
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