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# python.d.plugin
`python.d.plugin` is a netdata external plugin. It is an **orchestrator** for data collection modules written in `python`.
1. It runs as an independent process `ps fax` shows it
2. It is started and stopped automatically by netdata
3. It communicates with netdata via a unidirectional pipe (sending data to the netdata daemon)
4. Supports any number of data collection **modules**
5. Allows each **module** to have one or more data collection **jobs**
6. Each **job** is collecting one or more metrics from a single data source
## Disclaimer
Every module should be compatible with python2 and python3.
All third party libraries should be installed system-wide or in `python_modules` directory.
Module configurations are written in YAML and **pyYAML is required**.
Every configuration file must have one of two formats:
- Configuration for only one job:
```yaml
update_every : 2 # update frequency
retries : 1 # how many failures in update() is tolerated
priority : 20000 # where it is shown on dashboard
other_var1 : bla # variables passed to module
other_var2 : alb
```
- Configuration for many jobs (ex. mysql):
```yaml
# module defaults:
update_every : 2
retries : 1
priority : 20000
local: # job name
update_every : 5 # job update frequency
other_var1 : some_val # module specific variable
other_job:
priority : 5 # job position on dashboard
retries : 20 # job retries
other_var2 : val # module specific variable
```
`update_every`, `retries`, and `priority` are always optional.
---
## How to write a new module
Writing new python module is simple. You just need to remember to include 5 major things:
- **ORDER** global list
- **CHART** global dictionary
- **Service** class
- **_get_data** method
- all code needs to be compatible with Python 2 (**≥ 2.7**) *and* 3 (**≥ 3.1**)
If you plan to submit the module in a PR, make sure and go through the [PR checklist for new modules](https://github.com/netdata/netdata/wiki/New-Module-PR-Checklist) beforehand to make sure you have updated all the files you need to.
### Global variables `ORDER` and `CHART`
`ORDER` list should contain the order of chart ids. Example:
```py
ORDER = ['first_chart', 'second_chart', 'third_chart']
```
`CHART` dictionary is a little bit trickier. It should contain the chart definition in following format:
```py
CHART = {
id: {
'options': [name, title, units, family, context, charttype],
'lines': [
[unique_dimension_name, name, algorithm, multiplier, divisor]
]}
```
All names are better explained in the [External Plugins](../) section.
Parameters like `priority` and `update_every` are handled by `python.d.plugin`.
### `Service` class
Every module needs to implement its own `Service` class. This class should inherit from one of the framework classes:
- `SimpleService`
- `UrlService`
- `SocketService`
- `LogService`
- `ExecutableService`
Also it needs to invoke the parent class constructor in a specific way as well as assign global variables to class variables.
Simple example:
```py
from base import UrlService
class Service(UrlService):
def __init__(self, configuration=None, name=None):
UrlService.__init__(self, configuration=configuration, name=name)
self.order = ORDER
self.definitions = CHARTS
```
### `_get_data` collector/parser
This method should grab raw data from `_get_raw_data`, parse it, and return a dictionary where keys are unique dimension names or `None` if no data is collected.
Example:
```py
def _get_data(self):
try:
raw = self._get_raw_data().split(" ")
return {'active': int(raw[2])}
except (ValueError, AttributeError):
return None
```
More about framework classes
============================
Every framework class has some user-configurable variables which are specific to this particular class. Those variables should have default values initialized in the child class constructor.
If module needs some additional user-configurable variable, it can be accessed from the `self.configuration` list and assigned in constructor or custom `check` method. Example:
```py
def __init__(self, configuration=None, name=None):
UrlService.__init__(self, configuration=configuration, name=name)
try:
self.baseurl = str(self.configuration['baseurl'])
except (KeyError, TypeError):
self.baseurl = "http://localhost:5001"
```
Classes implement `_get_raw_data` which should be used to grab raw data. This method usually returns a list of strings.
### `SimpleService`
_This is last resort class, if a new module cannot be written by using other framework class this one can be used._
_Example: `mysql`, `sensors`_
It is the lowest-level class which implements most of module logic, like:
- threading
- handling run times
- chart formatting
- logging
- chart creation and updating
### `LogService`
_Examples: `apache_cache`, `nginx_log`_
_Variable from config file_: `log_path`.
Object created from this class reads new lines from file specified in `log_path` variable. It will check if file exists and is readable. Also `_get_raw_data` returns list of strings where each string is one line from file specified in `log_path`.
### `ExecutableService`
_Examples: `exim`, `postfix`_
_Variable from config file_: `command`.
This allows to execute a shell command in a secure way. It will check for invalid characters in `command` variable and won't proceed if there is one of:
- '&'
- '|'
- ';'
- '>'
- '<'
For additional security it uses python `subprocess.Popen` (without `shell=True` option) to execute command. Command can be specified with absolute or relative name. When using relative name, it will try to find `command` in `PATH` environment variable as well as in `/sbin` and `/usr/sbin`.
`_get_raw_data` returns list of decoded lines returned by `command`.
### UrlService
_Examples: `apache`, `nginx`, `tomcat`_
_Variables from config file_: `url`, `user`, `pass`.
If data is grabbed by accessing service via HTTP protocol, this class can be used. It can handle HTTP Basic Auth when specified with `user` and `pass` credentials.
`_get_raw_data` returns list of utf-8 decoded strings (lines).
### SocketService
_Examples: `dovecot`, `redis`_
_Variables from config file_: `unix_socket`, `host`, `port`, `request`.
Object will try execute `request` using either `unix_socket` or TCP/IP socket with combination of `host` and `port`. This can access unix sockets with SOCK_STREAM or SOCK_DGRAM protocols and TCP/IP sockets in version 4 and 6 with SOCK_STREAM setting.
Sockets are accessed in non-blocking mode with 15 second timeout.
After every execution of `_get_raw_data` socket is closed, to prevent this module needs to set `_keep_alive` variable to `True` and implement custom `_check_raw_data` method.
`_check_raw_data` should take raw data and return `True` if all data is received otherwise it should return `False`. Also it should do it in fast and efficient way.
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