The `starlark` aggregator allows to implement a custom aggregator plugin with a Starlark script. The Starlark
script needs to be composed of the three methods defined in the Aggregator plugin interface which are `add`, `push` and `reset`.
The Starlark Aggregator plugin calls the Starlark function `add` to add the metrics to the aggregator, then calls the Starlark function `push` to push the resulting metrics into the accumulator and finally calls the Starlark function `reset` to reset the entire state of the plugin.
The Starlark functions can use the global function `state` to keep temporary the metrics to aggregate.
The Starlark language is a dialect of Python, and will be familiar to those who
have experience with the Python language. However, there are major [differences](#python-differences).
Existing Python code is unlikely to work unmodified. The execution environment
is sandboxed, and it is not possible to do I/O operations such as reading from
files or sockets.
The **[Starlark specification][]** has details about the syntax and available
## The Starlark source can be set as a string in this configuration file, or
## by referencing a file containing the script. Only one source or script
## should be set at once.
##
## Source of the Starlark script.
source = '''
state = {}
def add(metric):
state["last"] = metric
def push():
return state.get("last")
def reset():
state.clear()
'''
## File containing a Starlark script.
# script = "/usr/local/bin/myscript.star"
## The constants of the Starlark script.
# [aggregators.starlark.constants]
# max_size = 10
# threshold = 0.75
# default_name = "Julia"
# debug_mode = true
```
## Usage
The Starlark code should contain a function called `add` that takes a metric as argument.
The function will be called with each metric to add, and doesn't return anything.
```python
def add(metric):
state["last"] = metric
```
The Starlark code should also contain a function called `push` that doesn't take any argument.
The function will be called to compute the aggregation, and returns the metrics to push to the accumulator.
```python
def push():
return state.get("last")
```
The Starlark code should also contain a function called `reset` that doesn't take any argument.
The function will be called to reset the plugin, and doesn't return anything.
```python
def push():
state.clear()
```
For a list of available types and functions that can be used in the code, see
the [Starlark specification][].
## Python Differences
Refer to the section [Python Differences](plugins/processors/starlark/README.md#python-differences) of the documentation about the Starlark processor.
## Libraries available
Refer to the section [Libraries available](plugins/processors/starlark/README.md#libraries-available) of the documentation about the Starlark processor.
## Common Questions
Refer to the section [Common Questions](plugins/processors/starlark/README.md#common-questions) of the documentation about the Starlark processor.
## Examples
- [minmax](/plugins/aggregators/starlark/testdata/min_max.star) - A minmax aggregator implemented with a Starlark script.
- [merge](/plugins/aggregators/starlark/testdata/merge.star) - A merge aggregator implemented with a Starlark script.
[All examples](/plugins/aggregators/starlark/testdata) are in the testdata folder.
Open a Pull Request to add any other useful Starlark examples.
