don't fetch indices , add indices to cache, and add esmonthly func

[kylebrandt]

No description provided.

[kylebrandt]

Currently if the time series is missing it errors inside ESDateHistrogram when it can't get the expected time series in the result. This result gets cached. Before when it would error on no indices in getFn, a wrapper for func (e ElasticHosts) Query(r *ElasticRequest) (*elastic.SearchResult, error), ensuring it was not cached. But now a lack of indices throws an error. Need to research inspecting the shards of the result and understanding what the means in this context.

[kylebrandt]

I think counting the resulting shards and erroring when there were no shards that matched will get the result I want.

However, it depends on the following PR olivere/elastic#373

Alternatively, I could go for the date math method mentioned in #1926 (comment) . But only if allow_no_indices applies to datemath and not just wildcard. According to the documentation it only applies to wildcard which I haven't tested yet. Even if does work I think the implementation will be a bit of pain.

[kylebrandt]

note: forgot to fmt, force pushed the fmt.

[captncraig]

probably use string(b) here. Don't want [42 31 13] in you key.

[captncraig]

additionally, what does the source have that causes it to be a different key? What varies?

[captncraig]

I ask because it surprises me that something like getting a cache key even has a possibility of erroring.

[kylebrandt]

fixes #1926