Carts

Stacki allows the admin to customize the software footprint of a backend node to enable additional functionality.

In a default setup, Stacki installs backend nodes with a very small software footprint. In Stacki parlance, the backend node is brought up to a ping and a prompt.

The backend node will have its network configured, and the SSH daemon is started to allow login access from the frontend.

To make the backend node more useful, other application software and services will need to be installed and configured.

There are several "levels" of installing applications in Stacki, we’re going to look at the simplest case. Assumptions are:

1. The application to be installed is available as an RPM
2. The application can be configured using simple shell command or a script.
3. The developer is has a basic knowledge of editing HTML-like syntax.

Stacki uses a collection of XML files that provide the definition of a system, and the instructions for installing a backend node. To extend the software footprint of a node, we will need to extend the XML framework to accommodate the extra functionality required.

The XML structure is not complicated - think of it as HTML with extra tags. The tags Stacki incorporates, map to kickstart elements you should already be familiar with: pre, post, main, package. From there it's mostly adding shell commands and scripts to install and configure applications.

For more information about the available XML tags, refer to the Wire Reference Guide

Introduction to Carts

Carts are created by end users in order to customize the configuration of backend nodes. For this section, we will walk through an example of creating a cart to add an Apache web server to backend nodes. We'll call this the apache cart.

First, we'll need to add the apache cart to the frontend:

# stack add cart apache

This will create the directory /export/stack/carts/apache and populate it with the following files and directories:

RPMS/
nodes/
nodes/cart-apache-backend.xml
graph/
graph/cart-apache.xml

In Stacki, backend node configuration is controlled by a collection of XML files. A node XML file contains the description of additional packages and configuration that should be applied to backend hosts. For this example, we will edit nodes/cart-apache-backend.xml and include a line that instructs Stacki to install the httpd package (the name of the Apache web server). Using your favorite editor, open nodes/cart-apache-backend.xml and you'll see:

<?xml version="1.0" standalone="no"?>
<kickstart>

	<description>
        apache cart backend appliance extensions
	</description>

        <!-- <package></package> -->

<!-- shell code for post RPM installation -->
<post>

</post>
</kickstart>

To add the httpd package, change the line:

<!-- <package></package> -->

To:

<package>httpd</package>

Next, we need to add code that runs in the post section (the section that executes after all packages are installed) that will enable the httpd server. To do that, change the section:

<post>

</post>

To:

<post>
/sbin/chkconfig --add httpd
/sbin/chkconfig httpd on
</post>

Now we need to associate the apache cart with the default distribution. This makes sure our modifications will be executed when backend nodes are installed.

A distribution is collection of pallets and carts. When you build a Stacki frontend, a distribution is automatically provided and it is called the default distribution. To see what pallets and carts are included in the default distribution, execute:

# stack list distribution

And you'll see:

NAME     OS     GRAPH   PALLETS                   CARTS
default: redhat default os-6.7-6.x stacki-2.0-6.x -----

This tells us that the default distribution is currently composed of the os and stacki pallets (and no carts).

We can associate our apache cart to the default distribution by executing:

# stack enable cart apache

And now stack list distribution shows us:

NAME     OS     GRAPH   PALLETS                   CARTS 
default: redhat default os-6.7-6.x stacki-2.0-6.x apache

The last step is to execute a command that binds the apache cart into the default distribution:

# stack create distribution

After the distribution is created, we can verify that our changes will be applied to a backend host when it installs. We can create a kickstart file for a backend host (in the command below, the backend host's name is backend-0-0), by executing:

# stack list host profile backend-0-0 > /tmp/ks.cfg	

If you open the file /tmp/ks.cfg, you'll see that httpd is listed in the packages section:

%packages --ignoremissing
foundation-rcs
httpd
libcap
ntp

And that our post section is in one of the post sections:

%post --log=/mnt/sysimage/var/log/stack-install.log

/sbin/chkconfig --add httpd
/sbin/chkconfig httpd on


%end

Now when a backend host is reinstalled, the Apache web server will automatically be up and running.

Adding New RPMS to a Cart

Download the RPM(s) for the application you want. Then you'll want to copy them into your cart.

For this example, we'll still be using the apache cart that we created above. Copy the RPM(s) into:

/export/stack/carts/apache/RPMS

And then execute:

# stack create distribution

If you want to add them on the fly, i.e. you don't want to reinstall your machines then execute:

# stack run host backend "yum clean all && yum -y install <rpmname>" \*

The above command will add rpmname to all your backend nodes.

To automatically apply the RPM rpmname to a backend node during installation, just add another package line as described above. For example, add the following line to your cart-apache-backend.xml node XML file:

<package>rpmname</package>

Remember, after you modify any file or directory in your cart, you must execute stack create distribution in order to apply that change to the default distribution.