Use bound id as dest in TTwitter thrift requests

[adleong]

When Linkerd proxies a TTwitter thrift request, it reads the dest header out of the message envelope and uses it as part of the identified service name. For example, if Linkerd receives a TTwitter request for a thrift service named service with dest: /foo then it will identify the request as /svc/foo/service. Linkerd also propagates the dest header on the outgoing message.

For Linkerd-to-Linkerd requests, this means that both the outgoing and incoming Linkerds receive the same value in the dest header and both do delegation based on this value. If the delegation results in a NameTree with weighted unions, a different choice could be made on the outgoing router vs the incoming router.

Instead of propagating the dest header, Linkerd could instead write the client id into the dest header of messages that it sends. This means that the incoming Linkerd would receive a dest header which is a concrete client name instead of the dest sent by the original client.

Note that this is a breaking behavioral change. Any services that depend on receiving the original value of the dest header will break.

See related: #950

[yllions]

hello, I want to know how can i add service name to twitter thrift 'dest' request header for finagle thrift client?

[adleong]

Hi @xiaoerlyl, unfortunately the finagle thrift client does not set the dest request header. Linkerd uses a special filter in order to set this header:

https://github.com/linkerd/linkerd/blob/master/linkerd/protocol/thrift/src/main/scala/com/twitter/finagle/buoyant/linkerd/TTwitterClientFilter.scala

[yllions]

@adleong thanks. This really helps.