Configurable geocoder

[cezio]

At the moment GHC is using freegeoip.net service to translate ip to location. This is 3rd party service, and can return errors unexpectedly. GHC could have pluggable geocoder backends, so other options (local copy of GeoIP from MaxMind for example) could be used too.

[justb4]

Makes sense. As each GeoIP provider will have its own custom protocol/format, a pluggable geocoder could be applied. The GHC Plugin system is very generic, based on Plugin base class, not just for Probes and Tests. As also notifications could be Plugins, a Plugin-based GeoIP provider is possible, easier, as no specific GUI is required.

[justb4]

Pasting comment from #216:

Via #216 GHC uses IP-API for now, so geocoding is working.

It would not bee too hard to use our Plugin system with IP-API as the default Plugin. Other providers can then be configured at will. Most will just need a url, key and return latitude, longitude in JSON, so all those could use a single Plugin class. Within the config_site.py, we just configure and parameterize the Plugin:

GEOIP = {
  'plugin': 'GeoHealthCheck.plugins.geoip.generic',
  'parameters': {
    'url_template': 'https://mygeoipprovider.com/?key=<mykey>&ip=%s&format=json',
    'lat_field': 'latitude',
    'lon_field': 'longitude'
  }
}

# default IP-API in config_main.py

GEOIP = {
  'plugin': 'GeoHealthCheck.plugins.geoip.generic',
  'parameters': {
    'url_template': 'http://ip-api.com/json/%s',
    'lat_field': 'lat',
    'lon_field': 'lon'
  }
}

# Create at runtime
geoip_provider = Factory.create_obj(CONFIG['GEOIP']['plugin'])
geoip_provider.init(CONFIG['GEOIP']['parameters'])
lat, lon = geoip_provider.lookup(ip)
# etc

This will cover most of the Geo-IP providers I've seen, or APIs on self-hosted Geo-IP Databases, or maybe even a local DB lookup, as @cezio suggests in #210. Our Plugin system can instantiate and parameterize the Plugin. Possibly this could be an array of geocoders, if one fails.