@Override
  public void channelActive(ChannelHandlerContext ctx) {
    channelActiveTimeMs = System.currentTimeMillis();
    logger.trace("Channel {} active", ctx.channel());
    this.ctx = ctx;
    nettyMetrics.channelCreationRate.mark();
  }
Netty calls this function when the channel is active.
<p/>
This is called exactly once in the lifetime of the channel. If there is no keepalive, this will be called
before the request (and the channel lives to serve exactly one request). If there is keepalive, this will be
called just once before receiving the first request.
@param ctx The {@link ChannelHandlerContext} that can be used to perform operations on the channel.
ambry-rest/src/main/java/com/github/ambry/rest/NettyMessageProcessor.java