Support SNI routing in bookkeeper

[sijie]

Descriptions of the changes in this PR:

Motivation

Netty supports sending SNI header on TLS handshake (https://github.com/netty/netty/issues/3801#issuecomment-104274440).

This PR uses that Netty feature to send SNI header while connecting to proxy software. So we can add proxy servers (e.g. Envoy, Nginx) in front of bookies.

Changes

• Add two configurations: bookieServiceUri and bookieConnectionMode. So the bookkeeper client can configure how it should connect to bookies.
• Send SNI header on TLS handshake

[sijie]

This is a draft to introduce sending SNI header in bookkeeper client. However, I think we need one more chance to make it work. Because in bookkeeper protocol, we use STARTTLS for promoting an insecure connection to TLS secured connection. That means we send requests before STARTTLS.

[eolivelli]

Now that we have advanced service discovery (BP-38) and the new BookieId abstraction (BP-41, not yet landed completely) the Bookie could publish a pure-TLS endpoint on discovery metadata (BookieServiceInfo) and then the client could use directly that information

[sijie]

@eolivelli Are you working on publishing a pure-TLS endpoint on discovery metadata?

[eolivelli]

@sijie I am not working on TLS, the mechanism of BP-41 is quite generic, so we will be free to support new protocols for the Bookie seamlessly in the future, once the BP-41 is finished (missing a couple of patches currently, but I feel it will be ready for BK 4.12.0)

[sijie]

@eolivelli okay will look into publishing a pure-TLS endpoint

[eolivelli]

@sijie PTAL here for the discovery mechanisms (BP-38) https://github.com/apache/bookkeeper/pull/2214/files

here (BP-41 part 1 - already landed to master branch) the client is now able to leverage BP-38 https://github.com/apache/bookkeeper/pull/2404

[eolivelli]

BP-41 has basically landed to master, so this work can move forward

[dlg99]

please update TLS tests with test for SNI