Dtab-Local HTTP header

[ashald]

Finagle encodes Dtab.local as a Dtab-Local HTTP header. Linkerd used to honor it for a while one way or another: originally it was supported "natively" and alter Linkerd moved to its own headers such as l5d-dtab. Before version 0.9 there were a backward compatibility so that Linkerd would append dtab-local to the l5d-dtab (#470). Although it was removed in #1089.

Even though it's now possible to inject a custom Dtab parser twitter/finagle@ce4ab7f and that's what Linkerd uses on its own, having to build your own parser for compatibility reasons is not very convenient.

It would b nice if it was possible to have an extra option that would make Linkerd to read Dtab from dtab-local in addition to l5d-dtab as it was doing before #1089

[adleong]

I can see why this would be useful for finagle apps. Would it work to simply have those apps include linkerd's Headers.Dtab.ClientFilter which will serialize the dtab local into the l5d-ctx-dtab header?

[ashald]

The main issue with including such a module is that every Finagle app that used to work "as is" will now require (1) an extra dependency on Linkerd codebase and (2) a re-build.
I think one of the beauties of Linkerd is that it can be used absolutely transparently from the application perspective. Even though it's very convenient for Linkerd itself, enforcing such changes means not only deep integration with Linkerd on the level of apps, but also that the main principle of being non-intrusive is not holding anymore. :(