By Items I think you mean metrics. Bosun learns about metrics, and their tag relationships when you do one of the following:
- Relay opentsdb data through Bosun (http://bosun.org/api#sending-data)
- Get copies of metrics sent to the api/index route http://bosun.org/api#apiindex
There are also metadata routes, which tell bosun about the metric, such as counter/gauge, unit, and description.
The logstash datasource will be deprecated in favor of an elastic datasource in the coming 0.5.0 release. But it is replaced by an elastic one is better (but requires ES 2+). To use those expressions see the raw documentation (bosun.org docs will updated next release): https://raw.githubusercontent.com/bosun-monitor/bosun/master/docs/expressions.md. To add it you would have something like the following in the config:
elasticHosts=http://ny-lselastic01.ds.stackexchange.com:9200,http://ny-lselastic02.ds.stackexchange.com:9200,http://ny-lselastic03.ds.stackexchange.com:9200
The functions to query various backends are only loaded into the expression library when the backend is configured.