Execute Service
The Execute Service allows a workflow to run external scripts or applications with any MediaPackage element as arguments. This provides a flexible way to operate with MediaPackage resources without the need to write Java code or build Opencast from source. Commands are executed on worker nodes.
There are two execute workflow operations:
- Execute Once: for running a single command that may operate on multiple elements of a mediapackage
- Execute Many: for running a command for each element in a mediapackage that matches the given criteria
Service Configuration
The Execute Service configuration in org.opencastproject.execute.impl.ExecuteServiceImpl.cfg must be updated to
define which commands may be run:
# Load factor
job.load.execute = 1.0
# The list of commands, separated by spaces, which may be run by the Execute Service.
# A value of * means any command is allowed.
# Default: empty (no commands allowed)
#commands.allowed =
If commands.allowed is empty or undefined (the default), the service won't be able to run any commands.
Use the special key * to permit any command to be executed (not recommended for production systems).
To adjust the job load factor for a command, use the load parameter in the workflow operation rather than
adjusting the job.load.execute parameter above.
Parameter substitution
The command arguments may contain placeholders, which are substituted by their corresponding values before the command runs. The complete list of available placeholders is detailed in the table below.
| Placeholder | Used in | Meaning |
|---|---|---|
| #{id} | Execute Once | The Mediapackage ID |
#{org_id} |
Execute Once, Execute Many | The organization ID |
| #{flavor(some/flavor)} | Execute Once | The absolute path of the element matching the specified flavor. If several elements have the same flavor, the first element is used. |
#{tag(download,-delete)} |
Execute Once | A list of tags used for selecting an element. You can exclude elements with certain tags using a minus prefix. If several elements are selected, the first element is used. |
| #{in} | Execute Many | The absolute path of the input element |
| #{out} | Execute Once, Execute Many | The absolute path of the output element, formed from the output-filename parameter |
Using custom properties in the argument list
Custom properties can be included in the command line by using the syntax #{name}, where name is the variable name,
as defined in the Execute Service's configuration file or in the global configuration file custom.properties.
The substitution will be done in the following order of precedence:
- Placeholders defined in the table above.
- Configuration keys defined in
org.opencastproject.execute.impl.ExecuteServiceImpl.cfg. - Configuration keys defined in
custom.properties.
For instance, suppose you use the Execute Service with the following arguments:
"John Doe" xyz #{my.property}
the command run will receive that argument list as-is, because my.property is not a valid placeholder, nor
is it defined in the Execute Service's configuration file or custom.properties.
However, if you define my.property in custom.properties:
my.property = foo
then the command will get the following argument list:
"John Doe" xyz foo
If you define the same variable in the Execute Service's configuration file (regardless of whether the variable
is defined in custom.properties or not):
my.property = bar
then the actual argument list will be:
"John Doe" xyz bar
Executing commands in workflows
For more information on how to execute a command in a workflow, see: