The hash you create in the role needs to match the definition of the attribute.
In this instance your role should look like:
default_attributes
'zabbix' => {
'agent' => {
'conf' => {
'Server' => 'zabbix-server1.com',
'ServerActive' => 'zabbix-server1.com'
}
}
}
See the Ruby DSL section of the Chef docs for a complete reference.
Note: the Chef convention is that attribute names should be all lower-case with underscores instead of Pascal/CamelCase. E.g. ServerActive
should be server_active
.