Merge pull request #26 from finagle/vk/finagle-with-netty4

Blog post about N4 support

source/blog/2017-02-06-finagle-loves-netty4.md

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+---
+layout: post
+title: Netty 4 support in Finagle
+published: true
+post_author:
+  display_name: Vladimir Kostyukov
+  twitter: vkostyukov
+tags: Finagle, Netty4
+---
+
+It's been quite a while since the [Netty 4 migration in Finagle][netty4-blog-post] was initially
+announced. We've travelled a long way and are happy to announce that there is now (as of
+[Finagle 6.42][6.42]) support for Netty 4 transports in most of the protocols: Thrift, ThriftMux,
+Memcached, MySQL, Kestrel, and Redis. Both HTTP/1.1 and HTTP/2 are coming soon!
+
+## How to enable Netty 4?
+
+While we have not yet defaulted to Netty 4, we've been running it in production for several months
+and have gained enough confidence to publicize the availability of the alternative transports in
+Finagle.
+
+We encourage Finagle users to try out the new Netty 4 transports for their protocols and jump on the
+fast track to upcoming changes around resiliency (think of HTTP/2) and performance (think of a
+reduced allocation profile and better threading model in Netty 4).
+
+To switch the transport over to Netty 4 supply the following command line flag:
+
+```
+-Dcom.twitter.finagle.toggle.flag.overrides=com.twitter.$protocol.UseNetty4=1.0
+```
+
+Where `$protocol` is one of the following: `mux` (use this for ThriftMux), `thrift`, `mysql`,
+`memcached`, `kestrel`.
+
+This command line flag overrides [a feature toggle][toggles] that is evaluated at application
+startup and is *global for all clients/servers running on the same JVM instance*.
+
+Note that Netty 4 is already enabled by default in `finagle-redis` so no need for an extra CLI flag.
+
+## What about HTTP/1.1?
+
+HTTP/1.1 on Netty 4 is still a work in progress. There are known limitations for HTTP clients, but
+we've been successfully running `finagle-http` servers with Netty 4 in production for several weeks
+and on [TwitterServer][ts]'s admin interface for several months.
+
+We feel confident in HTTP/1.1 servers running Netty 4 and encourage you to migrate now using the
+toggle override. Please note that this will also switch HTTP clients running in the same JVM
+process over to Netty 4, which we do not recommend at this point.
+
+```
+-Dcom.twitter.finagle.toggle.flag.overrides=com.twitter.http.UseNetty4=1.0
+```
+
+## What about HTTP/2?
+
+HTTP/2 (i.e., `finagle-http2`) should be considered beta as there are known issues with the ALPN
+support. We're hoping to roll out a feature-complete HTTP/2 implementation in the next couple of
+months. In the meantime, HTTP/2 support can be experimentally enabled on any Finagle HTTP client
+or server as shown below.
+
+```scala
+import com.twitter.finagle.Http
+
+val client = Http.client
+  .configured(Http.Http2)
+  .newService("www.example.com:80")
+```
+
+## What's next?
+
+We're quite optimistic about enabling Netty 4 by default in the next couple of months. Even though
+we're not there yet, we feel very proud of the work we've done and the progress we've made. It took
+us several years of engineering effort to be able to start serving Netty 4 traffic in production.
+
+## Where to report problems?
+
+Please file a [Github issue][github] if anything doesn't look right when Netty 4 is enabled.
+
+[netty4-blog-post]: http://finagle.github.io/blog/2014/10/20/upgrading-finagle-to-netty-4/
+[6.42]: https://github.com/twitter/finagle/releases/tag/finagle-6.42.0
+[toggles]: https://twitter.github.io/finagle/guide/Configuration.html#feature-toggles
+[github]: https://github.com/twitter/finagle/issues
+[ts]: https://github.com/twitter/twitter-server