Using Finagle's clientbuilder, how do I set the host externally? - proxy

Question

I am building a simple proxy to point to another server. Everything works but I need to find a way to be able to set the hosts in a ClientBuilder externally most likely using Docker or maybe some sort of configuration file. Here is what I have:
import java.net.InetSocketAddress
import com.twitter.finagle.Service
import com.twitter.finagle.builder.{ServerBuilder, ClientBuilder}
import com.twitter.finagle.http.{Request, Http}
import com.twitter.util.Future
import org.jboss.netty.handler.codec.http._
object Proxy extends App {
val client: Service[HttpRequest, HttpResponse] = {
ClientBuilder()
.codec(Http())
.hosts("localhost:8888")
.hostConnectionLimit(1)
.build()
}
val server = {
ServerBuilder()
.codec(Http())
.bindTo(new InetSocketAddress(8080))
.name("TROGDOR")
.build(client)
}
}
If you know of a way to do this or have any ideas about it please let me know!

Answer 1

if you want running this simple proxy in a docker container and manage the target host ip dynamically, you can try to pass a target host ip through environment variable and change your code like this
import java.net.InetSocketAddress
import com.twitter.finagle.Service
import com.twitter.finagle.builder.{ServerBuilder, ClientBuilder}
import com.twitter.finagle.http.{Request, Http}
import com.twitter.util.Future
import org.jboss.netty.handler.codec.http._
object Proxy extends App {
val target_host = sys.env.get("TARGET_HOST")
val client: Service[HttpRequest, HttpResponse] = {
ClientBuilder()
.codec(Http())
.hosts(target_host.getOrElse("127.0.0.1:8888"))
.hostConnectionLimit(1)
.build()
}
val server = {
ServerBuilder()
.codec(Http())
.bindTo(new InetSocketAddress(8080))
.name("TROGDOR")
.build(client)
}
}
this will let your code read system environment variable TARGET_HOST. when you done this part, you can try to start your docker container by adding the following parameter to your docker run command:
-e "TARGET_HOST=127.0.0.1:8090"
for example docker run -e "TARGET_HOST=127.0.0.1:8090" <docker image> <docker command>
note that you can change 127.0.0.1:8090 to your target host.

Answer 2

You need a file server.properties and put your configuration inside the file:
HOST=host:8888
Now get docker to write your configuration with every startup with a docker-entrypoint bash script. Add this script and define environment variables inside your Dockerfile:
$ ENV HOST=myhost
$ ENV PORT=myport
$ ADD docker-entrypoint.sh /docker-entrypoint.sh
$ ENTRYPOINT ["/docker-entrypoint.sh"]
$ CMD ["proxy"]
Write out your docker-entrypoint.sh:
#!/bin/bash -x
set -o errexit
cat > server.properties << EOF
HOST=${HOST}:${PORT}
EOF
if [ "$1" = 'proxy' ]; then
launch server
fi
exec "$#"
Launch Docker with your configuration and the command "proxy":
$ docker run -e "HOST=host" -e "PORT=port" image proxy
You can also do linking when your not sure of your server container ip adress:
$ docker run -e "HOST=mylinkhost" -e "PORT=port" --link myservercontainer:mylinkhost image proxy