External Plugins

Sawood Alam edited this page Dec 7, 2016 · 35 revisions

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netdata plugins

netdata supports several plugin methods:

Plugins using the native netdata plugin API (described below in detail), go to /usr/libexec/netdata/plugins.d/*.plugin. These can be written in any computer language (i.e. c, c++, go, lua, java, ruby, or whatever...).

Examples: https://github.com/firehol/netdata/tree/master/plugins.d

Additionally, netdata offers a set of modular plugins. They are modular since they accept custom made modules to be included. Writing modules for these plugins is easier than accessing the native netdata API directly.

  1. modules of the default bash plugin (charts.d.plugin), go to /usr/libexec/netdata/charts.d/*.chart.sh.

    Examples: https://github.com/firehol/netdata/tree/master/charts.d

  2. modules of the default python plugin (python.d.plugin), go to /usr/libexec/netdata/python.d/*.chart.py.

    Examples: https://github.com/firehol/netdata/tree/master/python.d

  3. modules of the default node.js plugin (node.d.plugin), go to /usr/libexec/netdata/node.d/*.node.js.

    Examples: https://github.com/firehol/netdata/tree/master/node.d

Each of these modular plugins has each own methods for defining modules. Please check the examples and their documentation.


native netdata plugin API

The information below is the standard netdata plugin API.

Any program that can print a few values to its standard output can become a netdata plugin.

There are 7 lines netdata parses. lines starting with:

  • CHART - create a chart
  • DIMENSION - add a dimension to the chart just created
  • BEGIN - initialize data collection for a chart
  • SET - set the value of a dimension for the initialized chart
  • END - complete data collection for the initialized chart
  • FLUSH - ignore the last collected values
  • DISABLE - disable this plugin

a single program can produce any number of charts with any number of dimensions each.

charts can also be added any time (not just the beginning).

command line parameters

The plugin should accept just one parameter: the number of seconds it is expected to update the values for its charts. The value passed by netdata to the plugin is controlled via its configuration file (so there is not need for the plugin to handle this configuration option). Check External Plugins Configuration

The script can overwrite the update frequency. For example, the server may request per second updates, but the script may overwrite this to one update every 5 seconds.

environment variables

There are a few environment variables that are set by netdata and are available for the plugin to use.

variable description
NETDATA_CONFIG_DIR The directory where all netdata related configuration should be stored. If the plugin requires custom configuration, this is the place to save it.
NETDATA_PLUGINS_DIR The directory where all netdata plugins are stored.
NETDATA_WEB_DIR The directory where the web files of netdata are saved.
NETDATA_CACHE_DIR The directory where the cache files of netdata are stored. Use this directory if the plugin requires a place to store data. A new directory should be created for the plugin for this purpose, inside this directory.
NETDATA_LOG_DIR The directory where the log files are stored. By default the stderr output of the plugin will be saved in the error.log file of netdata.
NETDATA_HOST_PREFIX This is used in environments where system directories like /sys and /proc have to be accessed at a different path.
NETDATA_DEBUG_FLAGS This is a number (probably in hex starting with 0x), that enables certain netdata debugging features. Check Tracing Options for more information.
NETDATA_UPDATE_EVERY The minimum number of seconds between chart refreshes. This is like the internal clock of netdata (it is user configurable, defaulting to 1). There is no meaning for a plugin to update its values more frequently than this number of seconds.

the output of the plugin

The plugin should output instructions for netdata to its output (stdout).

DISABLE

DISABLE will disable this plugin. This will prevent netdata from restarting the plugin. You can also exit with the value 1 to have the same effect.

CHART

CHART defines a new chart.

the template is:

CHART type.id name title units [family [context [charttype [priority [update_every]]]]]

where:

  • type.id

    uniquely identifies the chart, this is what will be needed to add values to the chart

    the type part controls the menu the charts will appear in

  • name

    is the name that will be presented to the user instead of id in type.id. This means that only the id part of type.id is changed. When a name has been given, the chart is index (and can be referred) as both type.id and type.name. You can set name to '', or null, or (null) to disable it.

  • title

    the text above the chart

  • units

    the label of the vertical axis of the chart, all dimensions added to a chart should have the same units of measurement

  • family

    is used to group charts together (for example all eth0 charts should say: eth0), if empty or missing, the id part of type.id will be used

    this controls the sub-menu on the dashboard

  • context

    the context is giving the template of the chart. For example, if multiple charts present the same information for a different family, they should have the same context

    this is used for looking up rendering information for the chart (colors, sizes, informational texts) and also apply alarms to it

  • charttype

    one of line, area or stacked, if empty or missing, the line will be used

  • priority

    is the relative priority of the charts as rendered on the web page, lower numbers make the charts appear before the ones with higher numbers, if empty or missing, 1000 will be used

  • update_every

    overwrite the update frequency set by the server, if empty or missing, the user configured value will be used

DIMENSION

DIMENSION defines a new dimension for the chart

the template is:

DIMENSION id [name [algorithm [multiplier [divisor [hidden]]]]]

where:

  • id

    the id of this dimension (it is a text value, not numeric), this will be needed later to add values to the dimension

  • name

    the name of the dimension as it will appear at the legend of the chart, if empty or missing the id will be used

  • algorithm

    one of:

    • absolute

      the value is to drawn as-is (interpolated to second boundary), if algorithm is empty, invalid or missing, absolute is used

    • incremental

      the value increases over time, the difference from the last value is presented in the chart, the server interpolates the value and calculates a per second figure

    • percentage-of-absolute-row

      the % of this value compared to the total of all dimensions

    • percentage-of-incremental-row

      the % of this value compared to the incremental total of all dimensions

  • multiplier

    an integer value to multiply the collected value, if empty or missing, 1 is used

  • divisor

    an integer value to divide the collected value, if empty or missing, 1 is used

  • hidden

    giving the keyword hidden will make this dimension hidden, it will take part in the calculations but will not be presented in the chart

data collection

data collection is defined as a series of BEGIN -> SET -> END lines

BEGIN type.id [microseconds]

  • type.id

    is the unique identification of the chart (as given in CHART)

  • microseconds

    is the number of microseconds since the last update of the chart. It is optional.

    Under heavy system load, the system may have some latency transferring data from the plugins to netdata via the pipe. This number improves accuracy significantly, since the plugin is able to calculate the duration between its iterations better than netdata.

    The first time the plugin is started, no microseconds should be given to netdata.

SET id = value

  • id

    is the unique identification of the dimension (of the chart just began)

  • value

    is the collected value

END

END does not take any parameters, it commits the collected values for all dimensions to the chart. If a dimensions was not SET, its value will be empty for this commit.

More SET lines may appear to update all the dimensions of the chart. All of them in one BEGIN -> END block.

All SET lines within a single BEGIN -> END block have to refer to the same chart.

If more charts need to be updated, each chart should have its own BEGIN -> SET -> END block.

If, for any reason, a plugin has issued a BEGIN but wants to cancel it, it can issue a FLUSH. The FLUSH command will instruct netdata to ignore all the values collected since the last BEGIN command.

If a plugin does not behave properly (outputs invalid lines, or does not follow these guidelines), will be disabled by netdata.

collected values

netdata will collect any signed value in the 64bit range: -9.223.372.036.854.775.808 to +9.223.372.036.854.775.807

Internally, all calculations are made using 128 bit double precision and are stored in 30 bits as floating point.

If a value is not collected, leave it empty, like this:

SET id =

or do not output the line at all.

Skeleton Plugins

  1. python, use python.d.plugin, there are many examples in the python.d directory

    python is ideal for netdata plugins. It is a simple, yet powerful way to collect data, it has a very small memory footprint, although it is not the fastest way to do it.

  2. node.js, use node.d.plugin, there are a few examples in the node.d directory

    node.js is the fastest scripting language for collecting data. If your plugin needs to do a lot of work, compute values, etc, node.js is probably the best choice before moving to compiled code. Keep in mind though that node.js is not memory efficient; it will probably need more RAM compared to python.

  3. BASH, use charts.d.plugin, there are many examples in the charts.d directory

    BASH is the simplest scripting language for collecting values. It is the less efficient though. You can use it to collect data quickly, but extensive use of it might use a lot of system resources.

  4. C, use apps.plugin

    Of course, C is the most efficient way of collecting data. This is why netdata itself is written in C too.

Writing Plugins Properly

There are a few rules for writing plugins properly:

  1. Respect system resources

    Pay special attention to efficiency:

    • Initialize everything once, at the beginning. Initialization is not an expensive operation. Your plugin will most probably be started once and run forever. So, do whatever heavy operation is needed at the beginning, just once.
    • Do the absolutely minimum while iterating to collect values repeatedly.
    • If you need to connect to another server to collect values, avoid re-connects if possible. Connect just once, with keep-alive (for HTTP) enabled and collect values using the same connection.
    • Avoid any CPU or memory heavy operation while collecting data. If you control memory allocation, avoid any memory allocation white iterating to collect values.
    • Avoid running external commands when possible. If you are writing shell scripts avoid especially pipes (each pipe is another fork, a very expensive operation).
  2. The best way to iterate at a constant pace is this pseudo code:

    var update_every = argv[1] * 1000; /* seconds * 1000 = milliseconds */
    
    readConfiguration();
    
    if(!verifyWeCanCollectValues()) {
      print "DISABLE";
      exit(1);
    }
    
    createCharts(); /* print CHART and DIMENSION statements */
    
    var loops = 0;
    var last_run = 0;
    var next_run = 0;
    var dt_since_last_run = 0;
    var now = 0;
    
    FOREVER {
       /* find the current time in milliseconds */
       now = currentTimeStampInMilliseconds();
    
       /*
        * find the time of the next loop
        * this makes sure we are always aligned
        * with the netdata daemon
        */
       next_run = now - (now % update_every) + update_every;
    
       /*
        * wait until it is time
        * it is important to do it in a loop
        * since many wait functions can be interrupted
        */
       while( now < next_run ) {
           sleepMilliseconds(next_run - now);
           now = currentTimeStampInMilliseconds();
       }
    
       /* calculate the time passed since the last run */
       if ( loops > 0 )
           dt_since_last_run = (now - last_run) * 1000; /* in microseconds */
    
       /* prepare for the next loop */
       last_run = now;
       loops++;
    
       /* do your magic here to collect values */
       collectValues();
    
       /* send the collected data to netdata */
       printValues(dt_since_last_run); /* print BEGIN, SET, END statements */
    }

    Using the above procedure, your plugin will be synchronized to start data collection on steps of update_every. There will be no need to keep track of latencies in data collection.

    Netdata interpolates values to second boundaries, so even if your plugin is not perfectly aligned it does not matter. Netdata will find out. When your plugin works in increments of update_every, there will be no gaps in the charts due to the possible cumulative micro-delays in data collection. Gaps will only appear if the data collection is really delayed.

  3. If you are not sure of memory leaks, exit every one hour. Netdata will re-start your process.

  4. If possible, try to autodetect if your plugin should be enabled, without any configuration.