perf: eliminate repeated route lookups in http filters

[rshriram]

The rate limit filter and the fault filter can be applied to specific upstream clusters. Currently, these filters recompute the route on their own. For performance reasons, this recomputation should be avoided. Instead, the upstream cluster chosen by the http connection manager should be made available via the some accessible interface.

[mattklein123]

The return value here should be cached: https://github.com/lyft/envoy/blob/master/source/common/http/conn_manager_impl.h#L255

[mattklein123]

In thinking about this a little bit more it's not so simple, since the current interface takes the headers as a parameter, and the headers might potentially be modified between filters. Need to think a little more about this.

[rshriram]

Question is do filters want the route chosen by the http connection manager or do they want to compute a route with custom headers ? May be both depending on the scenario. But for majority of use cases, I can see that folks will want to know which cluster or route was chosen by the connection manager. That can certainly be cached right? At the same time, if some filter wants to recompute the route by itself, it can do so using the current way. WDYT ?

On Fri, Jan 27, 2017 at 4:42 PM Matt Klein ***@***.***> wrote: In thinking about this a little bit more it's not so simple, since the current interface takes the headers as a parameter, and the headers might potentially be modified between filters. Need to think a little more about this. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#372 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AH0qdwkvEyG2gk40cl-XHmJda_WFQhDfks5rWmTYgaJpZM4LrwRn> .

-- ~shriram

[mattklein123]

See the linked PR. In general, I agree that eventually we might want to allow a filter to lookup based on headers, but the reality is that nothing needs that right now. I would rather keep it simple into that requirement comes back. The attached PR simplifies things and is a lot faster in the common case.