private void closeChannel(ChannelHandlerContext ctx, ChannelPromise promise) {
        Channel child = ctx.channel();
        Channel parent = HttpUtils.getMainChannel(ctx);

        // 1. Check if already_closing flag on this stream channel. If there is, then success this promise and return.
        //    If not, then add already_closing flag to this stream channel.
        // 2. Check if already_closing flag on the parent channel.
        //    If so, then just return.
        //    If not, then set already_closing on parent channel, and then allow through.

        if (isAlreadyClosing(child)) {
            promise.setSuccess();
            return;
        }

        if (isAlreadyClosing(parent)) {
            return;
        }

        // Close according to the specified close type.
        ConnectionCloseType closeType = ConnectionCloseType.fromChannel(parent);
        Integer port =
                parent.attr(SourceAddressChannelHandler.ATTR_SERVER_LOCAL_PORT).get();
        port = port == null ? -1 : port;
        incrementCounter(closeType, port);
        switch (closeType) {
            case DELAYED_GRACEFUL:
                gracefullyWithDelay(ctx.executor(), parent, promise);
                break;
            case GRACEFUL:
            case IMMEDIATE:
                immediate(parent, promise);
                break;
            default:
                throw new IllegalArgumentException("Unknown ConnectionCloseEvent type! - " + closeType);
        }
    }
Look on both the stream channel, and the parent channel to see if the CLOSE_AFTER_RESPONSE flag has been set.
If so, return that promise.

@param ctx
@param parent
@return
zuul-core/src/main/java/com/netflix/netty/common/Http2ConnectionCloseHandler.java