Well, this is not really true... "http-source" is just a name, it could be whatever other string. The key point is this name must match the one appearing in the source configuration. I.e. if our source is called "wonderful-source":

    orionagent.sources = wonderful-source

Then the related configuration must be:

    orionagent.sources.wonderful-source.type = org.apache.flume.source.http.HTTPSource
    orionagent.sources.wonderful-source.channels = notifications
    ...

Please observe the line

    orionagent.sources.wonderful-source.type = org.apache.flume.source.http.HTTPSource

is the one really governing the supported options.