Automate Your Application on the Cloud with Cloudify Custom Commands

Posted By: Tamir Korem on July 19, 2012


Your Application is Installed on a Cloud. Now What ?

Ok, so you installed an application on a cloud and now you want to update it, replace your .war file, modify the DB schema etc.
I guess, some of the following thoughts may run in your head : “Now I need to login to the VM on the cloud (via ssh)”, “Where’s my Key-Pair file? Was is pem or ppk?”, “Do I have permissions to change files on the cloud?”, “I wish there was a way I could automate this process”.

In this post, I will walk you through Cloudify’s Custom Commands Mechanism.

Cloudify Custom Commands enable admin users or third-party tools to remotely manage service instances, which is especially useful when remote service APIs aren’t available.
They can also come in handy in cross-service manipulations, where one service manipulates another service in the application, thus enabling static applications to become much more dynamic without replacing the stack.

All you need to do is add a few lines to your recipe file and you’re good to go.

How to Create Custom Commands

Cloudify provides this mechanism by allowing you to describe Custom Commands using Groovy closures, external Groovy scripts, or external shell/batch scripts.
The commands can be parameterized, and they can be invoked by using the Cloudify shell or automatically by the lifecycle event handlers when certain conditions are met.

You need to add a customCommands section in the main section of the recipe’s service file.
The customCommands section should contain an array of custom commands and their descriptions.
Each custom command must be in the following format (syntax):
"customCommandName" : groovy closure code or a script to run


The following code snippet demonstrates several general examples:

Custom Commands Use Cases

In general, custom commands can be very useful in any of the following:

  1. Continuous deployment (e.g. updating a war file)
  2. Reconfiguration of services (e.g. changing a db schema, or apache load balancer configuration or re-running a chef-client)
  3. Triggering an arbitrary operation on the service (e.g. invoke a load command on the apacheLB)

How to Use It

In order to invoke a custom command from the Cloudify shell, run the following command:
  invoke serviceName customCommandName [param1] [param2] ... [paramN]

Custom commands can also be invoked by another service as described in the following code snippet and in the examples below.

Examples:

Here are some helpful custom commands that we have already implemented in our sample recipes:

Example 1: Dynamically Updating Your Apache Load Balancer

We added two custom commands: to the apacheLB recipe: addNode and removeNode, which update the configuration of the apache load balancer module with new/removed nodes members.

Here’s the code snippet in the apacheLB-service.groovy :

As you can see, in apacheLB-service.groovy, there are two custom commands: addNode and removeNode. You need to add a postStart lifecycle event to each service whose instances you want add to the load balancer configuration. You need to add a postStop lifecycle event to each service whose instances you want removed from the load balancer configuration.
For example, these commands are invoked during the postStart and postStop lifecycle event handlers
,of the tomcat service in the PetClinic Recipe.

The following presentation illustrates how the Custom Commands Machanism works with Apache and tomcat, from the installation of the services to modifying the apacheLB configuration by invoking custom commands:

Example 2: Testing Your Load Balancer Under Heavy Loads

On every machine on which apache is installed, you will also find the ab command which is a server benchmarking tool provided with the Apache HTTP distribution.
In the apacheLB recipe, you can find a "load" custom command that uses ab, thus enabling you to test your application under load, by using the recipe’s load custom command.

Here’s the "load" code snippet in apacheLB-service.groovy :

Example 3: Updating Your Application

Let’s say, you installed a tomcat web server and deployed your war file on it (with Cloudify).
Now you have a newer version of the war file.

All you need to do is to run the following custom command:
  invoke tomcat updateWar NEW_WARFILE_FULL_URL_PATH

Here’s the "update_war" code snippet in tomcat-service.groovy :

Oh, And One More Thing

As always with Cloudify, it works on every cloud and every OS: EC2, OpenStack, Rackspace you name it, Windows and Linux (Centos or Ubuntu).

So don’t hesitate to give a test drive and let us know what you think.

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