A collectd Python plugin to read Prometheus metrics endpoints

1. Find out which version of Python your collectd is built against to know which python/pip binary to use. So e.g. with Debian:

   $ dpkg -S python.so | grep collectd
   collectd-core: /usr/lib/collectd/python.so
   $ ldd /usr/lib/collectd/python.so | grep python
   libpython2.7.so.1.0 => /usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0 (0x00007f953a5c2000)
   $
   

   which uses Python 2.7 still so I need to use pip2 when installing the dependencies.
2. Install collectd-prometheus:

   # pip2 install collectd-prometheus
   

1. Create a collectd configuration e.g. /etc/collectd/collectd.conf.d/prom-service.conf

LoadPlugin python
<Plugin python>
    Import "collectd_prometheus"
    <Module "collectd_prometheus">
       Interval 30 # How often to scrape metrics. This is the default, can be omitted
       <Process>
           Process "mycoolservice" # Name this instance, e.g. after what service you're scraping
           Protocol "http" # This is default, can be omitted
           Host "127.0.0.1" # This is default, can be omitted
           Port "8080" # This is default, can be omitted
           Filter "only|these" # A regex which matches the names of the metrics you only want to include
           Filter "metrics" # You can even specify multiple regexes
       </Process>
       # Scrape another another service as well, e.g.
       <Process>
           Process "anothercoolservice"
           # This time we use the defaults, except Port
           Port "8081"
       </Process>
    </Module>
</Plugin>

In Python, using a virtual environment is the recommended way to isolate your applications dependencies from other applications. To use a virtualenv with collectd we have to create one, activate it, install our package into it.

1. Using the steps listed Installation figure out which Python version collectd uses.

2. If python3 use venv which is included in Python 3. When using Python 2.7, we have to install virtualenv which can be packaged in your OS/distribution (python-virtualenv in Debian) or you install it manually, see the linked documentation.

3. Create your virtualenv where you want to store it, e.g:

   # python -m virtualenv /usr/lib/collectd/prom
   

4. Activate it and install our package, e.g.:

   # source /usr/lib/collectd/prom/bin/activate
   (prom) # pip install collectd-prometheus
   

5. Find your virtualenvs site-packages folder, e.g:

   # find /usr/lib/collectd/prom/ -type d -iname "site-packages"
   /usr/lib/collectd/prom/lib/python2.7/site-packages
   

6. Configure collectd to look for collectd-prometheus and it's dependencies in the directory that you found in step 5. E.g:

   LoadPlugin python
   <Plugin python>
       ModulePath "/usr/lib/collectd/prom/lib/python2.7/site-packages" # Right here
       Import "collectd_prometheus"
   […]