Using CA AppLogic › Appliance Developer Guide › Appliance Overview › Configure Appliance › Tie Boundary to Interior › Startup and Hooks

Startup and Hooks

The most important aspects of tying an interior to the boundary are performed during the appliance startup. During the appliance boot process, the APK has two functions:

• Retrieve and apply the appliance configuration, such as properties, volume setup and network connections
• Report the status to AppLogic

For example, early in the configuration process, the APK performs the following:

• Reads appliance-specific customization in the applogic_init config file

  The applogic_init config file allows you to change which aspects of the OS configuration are auto-configured by APK.

• Retrieves the appliance configuration, such as property values, network configuration, and volume configuration
• Stores the property values in text file formats. These formats vary by OS
• Optionally edits third party configuration files to apply specific property values, if configured.
• Configures the network terminals and raw interfaces according to how the appliance is connected in the application
• Configures the public-key login for the ssh daemon which allows users with appropriate permissions to login to the appliance
• Optionally auto-mounts volumes, if specified in the class descriptor
• Writes the Appliance Instance Descriptor

  The Appliance Instance Descriptor contains OS-specific information, such as device names of all network interfaces and disk volumes. When you add this specific appliance class to an application, you make an instance of that class with the specific values for the configurable properties and connections to other appliances and/or to the outside world. This specific configuration, in its entirety, is passed to the virtual appliance, when it is started.

Appliance Startup Script

After the early configuration completes and the essential OS starts, the Appliance Startup Script begins. This optional script allows you to tailor the appliance boundary properties to meet the specific functionality of your software product in the appliance. The APK provides one configuration file and one hook for the script. The file location is OS-specific. For example, the file is located in /etc/sysconfig/ for Posix-style operating systems, such as Linux and BSD, and in \applogic\config\ for Windows operating systems.

The files are:

• applogic_init - provides configuration options for defining the aspects of the OS setup performed automatically by the APK and specifies configuration files where the APK will apply property settings. The presence of this file is optional. The APK has defaults for all settings allowed in the file. For additional information, refer to customize appliance behavior in Linux appliances or Windows appliances.
• applogic_appliance - provides a late-setup hook that runs just before the APK reports the startup status to CA AppLogic. You can use this hook to perform appliance-specific configuration and/or launch services. The hook is expected to the return status and, on failure, also print a one-line message to the standard error output stream. This message displays on the grid dashboard.

In addition, the appliance can use OS-provided startup functionality, such as sys5 init in Linux or service control manager in Windows.

Appliance-Specific Startup Check Script

After the appliance specific startup completes, the APK optionally executes the appliance-specific startup check script. The script, if present, verifies the appliance started and returns a success or failure message to the grid controller. If no script is present or the script returns no error, the appliance startup check sends a successful start. If script returns an error, the appliance startup check stops and sends the failure message.

Appliance Instance Descriptor

The Appliance Instance Descriptor contains OS-specific information, such as the device names of all network interfaces and disk volumes. When you add this specific appliance class to an application, you make an instance of that class with specific values for the configurable properties and connections to other appliances and/or to the outside world. This specific configuration, in its entirety, is passed to the virtual appliance, when it is started.

When you configure and start an application, the corresponding instance descriptor contains information similar to this:

property weight: integer, value=37 # appliance was configured with specific value
volume data:  dev=/dev/sdc, mount=/opt # configured, appears as /dev/sdc # to the operating system
volume cache: disconnected # optional, app designer chose not to configure it

Automatic Configuration File Update

In many cases, the appliance properties correspond directly to strings that need to be inserted into an appliance-specific configuration file. In such cases, rather than writing code to read one of the APK-provided property files and generate the appropriate configuration files on each boot, you can instruct APK to apply the property values directly to the configuration files.

This can be done in all cases where the following conditions are met:

• Appliance has a writable disk volume. This method is not suitable for an appliance whose volumes are all read-only.
• Property value needs to be simply inserted into the configuration file
• Configuration file is a text file
• Configuration file format allows for adding comments to it, and the program(s) using it either do not modify the file, or re-write it keeping the comments intact.

To set up APK to do automatic config file updates on boot:

• Instrument the configuration files with special comments that specify exactly where the property values are to be inserted. The instrumentation syntax can be found in the Application Descriptor Language Overview in the ADL Reference Guide.

  ADL Property Markup is a language for describing applications within the application model where applications are built out of multiple components, with each component being an instance of a virtual appliance with its own OS and application software. In the interpretation of ADL, host and hardware or any type of resource do not necessarily correspond to physical resources. They may be virtual devices that share the same hardware.

  ADL is based on UDL, a generic language for describing hierarchically structured data in plain ASCII text form. You can find the description of UDL in a separate document; however, understanding UDL in general is not necessary. This document contains a complete description of the ADL syntax.

• Configure the list of files to be updated in the APK_CONFIG_FILES setting in the applogic_init configuration file.