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26 Oct 2016


inspired by the shackspace’s grafana usage for moisture/temperature monitoring i wanted to use grafana myself. since i’m also active in the fablab neckar-alb and we are having a nice project, called cycle-logistics tübingen, to monitor this seemd to be a good opportunity to apply this toolchain.

we are interested in the voting behaviour:

this blog posting documents all steps needed to rebuild the setup so you can leverage this toolchain for your own projects!

here is a screenshot of how it looks:


below you can find a detailed listing and discussion of the single programs used. the source code can be found on github, except the nixos specific parts which is listed below exclusively.


selenium is used to visit, parse the DOM tree and to export the data as data.json.

to execute one needs an python environment with two additional libraries. nix-shell along with collect_data-environment.nix is used to create that environment on the fly.

#! /usr/bin/env nix-shell
#! nix-shell collect_data-environment.nix --command 'python3'

from selenium import webdriver
from selenium import selenium
from selenium.webdriver.common.keys import Keys

from import By
from import WebDriverWait # available since 2.4.0
from import expected_conditions as EC # available since 2.26.0
from pyvirtualdisplay import Display

import sys
import os

display = Display(visible=0, size=(800, 600))

from distutils.version import LooseVersion, StrictVersion
if LooseVersion(webdriver.__version__) < LooseVersion("2.51"):
    sys.exit("error: version of selenium ("
        + str(LooseVersion(webdriver.__version__))
        + ") is too old, needs 2.51 at least")

ff = webdriver.Firefox()

st = ""

v = ff.execute_script("""
var t = document.getElementById('profile').childNodes; 
var ret = []
for (var i = 0; i < t.length; i++) {
  if ('id' in t[i]) {
    if(t[i].id.includes('profil-')) {
      var myID = t[i].id.replace("profil-","");
      var myVotes = t[i].getElementsByClassName('profile-txt-stimmen')[0].innerHTML;
      var myTitle = t[i].getElementsByClassName('archive-untertitel')[0].innerHTML;
      var myVerein = t[i].getElementsByClassName('archive-titel')[0].innerHTML;
      //console.log(myID,myVerein, myTitle, myVotes)
      var r = new Object();
      r.Id = parseInt(myID);
      r.Votes = parseInt(myVotes);
      r.Verein = myVerein; 
      r.Title = myTitle;
var date = new Date();
var exp = {};
exp.Date = date;
exp.Data = ret;
var j = JSON.stringify(exp,  null, "\t");
return j;

print (v)



info: in the above environment, two different versions of nixpkgs are mixed, which is a nix speciality.

virtual-display and selenium from an older nixpkgs base called pkgs1 while firefox is the one coming with the nixos operating system called pkgs.

golang import

the go based importer is very simple and basically follows the example from the influxdb client code base.

if you want to build the inject_into_fluxdb binary you can simply use nix-shell and inside that shell simply type go build. you have to put that binary into the right place, which is /var/lib/crawler/, manually since this was only a prototype.

warning use nixos-rebuild switch with the nixos specific changes from below first so that the nixos system will create the user/group and directory (crawler/crawler and /var/lib/crawler). and when you deploy stuff into that directory, make sure you use chown crawler:crawler . -R in that directory.



go2nix in version 1.1.1 has been used to generate the default.nix and deps.nix automatically. this is also the reason for the weird directory naming inside the GIT repo.

warning there are two different implementation of a go to nix dependency converter and both are called go2nix. i was using the one from kamilchm the other never worked for me.


info: go2nix generates a default.nix which is basically a dropin when used in nixpkgs but i wanted to use it with nix-shell so a few lines needed changes. just be awere of that!



info: in the configuration.nix excerpt apache, which is called httpd in nixos`, is used as a reverse proxy. you don’t have to follow that example but it is a nice setup once one gets it working.

  imports =
    [ # Include the results of the hardware scan.
  services.grafana = {
    security = {
    users = {
      allowSignUp = false;
      allowOrgCreate = true;
    analytics.reporting.enable = false;


  services.influxdb = {
    enable = true;
  services.httpd = {
    enable = true;
    enablePHP = true;
    logPerVirtualHost = true;
    hostName = "";
    extraModules = [
      { name = "php7"; path = "${pkgs.php}/modules/"; }
      { name = "deflate"; path = "${pkgs.apacheHttpd}/modules/"; }
      { name = "proxy_wstunnel"; path = "${pkgs.apacheHttpd}/modules/"; }
 virtualHosts =
      # (https)
        hostName = "";
        serverAliases = [ "" "" ];

        documentRoot = "/www/";
        enableSSL = true;
        sslServerCert = "/ssl/acme/";
        sslServerKey = "/ssl/acme/";
       extraConfig = ''
          Alias /.well-known/acme-challenge /var/www/challenges/
          <Directory "/var/www/challenges/">
            Options -Indexes
            AllowOverride None
            Order allow,deny
            Allow from all
            Require all granted
          RedirectMatch ^/$ /main/
          #Alias /main /www/
          <Directory "/www/">
            Options -Indexes
            AllowOverride None
            Require all granted

          SetOutputFilter DEFLATE

          <Directory "/www/">
            Options -Indexes
            AllowOverride None
            Order allow,deny
            Allow from all

          # prevent a forward proxy! 
          ProxyRequests off

          # User-Agent / browser identification is used from the original client
          ProxyVia Off
          ProxyPreserveHost On

          RewriteEngine On
          RewriteRule ^/grafana$ /grafana/ [R]

          <Proxy *>
          Order deny,allow
          Allow from all

          ProxyPass /grafana/ retry=0
          ProxyPassReverse /grafana/


simply put crawler.nix into /etc/nixos and reference it from configuration.nix using the imports directive.

info: note the timerConfig.OnCalendar setting which starts the crawling every 30 minutes.



this is an example of the data.json which is generated by selenium and with jq, a very nice tool to process json in a shell, one can experiment with the values.

jq usage example

cat data.json | jq '.Data[0]'
  "Id": 338,
  "Votes": 2252,
  "Verein": "Ziegenprojekt am Jusi und Florian",
  "Title": "Schwäbischer Albverein Kohlberg/Kappishäuseren"

grafana setup

first you need to add an influxdb data source:

based on that you need to configure the graph to use the influxdb source:


hope you enjoyed reading this and if you have further questions, drop an email to: