1. Configuration Parameters
2. userData Templates

When you are requesting a new Virtual Machine you have to specify a URL where the plugin can find the configuration parameters that describe the structure and the functionality of the instance. This URL is called VM Configuration Point (VMCP).

The document itself is a JSON file that describes the session information. For example:

{
    "name": "MyAwesomeVM",
    "secret": "mg041na39123",
    "vcpus": 1,
    "memory": 512,
    "cernvmVersion": "1.18-2",
    "flags": 8,
    "userData": "[amiconfig]\nplugins=cernvm\n[cernvm]\nusers=user:users;password",
    "signature": "01ba4719c80b6fe911b091a7c05124b64eeece964e09c058ef8f9805daca546b"
}

For security purposes, these information must be signed with your private key. For details on how to calculate the signature check the Calculating VMCP Signature document.

When the CernVM Web API Plugin requests the VMCP URL it always appends the following parameters:

For example, when you request:

core.requestSession("https://example.com/vmcp.php?vm=1123", success_callback, failure_callback );

The plugin will append the other two parameters, eventually requesting:

https://example.com/vmcp.php?vm=1123&cvm_salt=a8h4f9v7h4w7242iuyaf&cvm_hostid=adc83b19e793491b1c6ea0fd8b46cd9f32e592fc

The following VMCP parameters are handled by the plugin:

It is possible to include macro variables to the userData. The values for those macros can be specified via the start({ }) function.

Each macro follows the following syntax:

${variable_name[:default]}

For example, here are some contextualization information that allows the user to specify his own username and password. If not specified, the default user will be 'user' with no password.

[amiconfig]
plugins=cernvm

[cernvm]
users=${username:user}:users:${password}

You can then specify the values from javascript:

session.start({
   'username': 'john',
   'password': 'secret'
});