What Component Connects MCU to WiFi/Bluetooth Module in IoT Device Network?

Hi I know almost next to nothing about EE...but I have gotten a question about a missing component in my network idea. Would be great if someone can point me to the right direction.

So basically I want my device to able to communicate with my back-end server. The route is as follow...

Device (made by supplier, with on board MCU)

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? (what is this missing component?)

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Chip (wifi / BLT module)

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router

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cloud

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back end Server

Thank you so much...

Well, we would need a bit more information about the board at the top of your diagram and the chip or module. If your board can be programmed to provide the proper driver to format your data and drive your RF (BT / WiFi / etc) device, the only part you need is whatever physical interface there is. If the board is merely producing a signal or data (say, a serial port), then your missing element is a communications processor to format the data and provide what the module needs. But then, that also depends on the module. For example, if you use a ESP-8266 - based module or a Particle Photon, you can program those to take care of these functions and they can connect directly to your board.
Hope this helps somewhat. Perhaps you can provide more details about what you are working with?
Charles

Your chip would normally have the appropriate stack for the protocol on board, and commonly use a serial link and an  AT command set. Whatever your device is, you presumably have data that needs to be sent, so it needs an appropriate software and hardware interface, if it has a serial port it is probably RS232 or USB.So as a minimum you will need something like an interface cable and an RS232 to TTL converter, worst case another small processor card that will handle the hardware protocols and firmware to repackage the data for the wireless module.A bit more information on the Device and the Chip would help,cheers,Richard

Hi and thank you so much for the replies. 
That thing is more like an adapter that I will need to convert whatever I can retrieve from the the device MCU to something meaningful through the broadcasting chip.I wont be able to program the MCU but merely taking signals from it...Lets say some analogue signal I will be retrieving, but those need to be interpreted before broadcast? And that's what the "missing component" I think should do...?

Or according to your replies I can program the RF chip to allow it to interpret the analog signal directly, hence there is no need for the signal converting? 
For more info on the background...we have some ovens that we would like to be able to control and communicate through our network. Right now I think we have the ability to read the signals from the oven's MCU and control it as well, but not sure the complexity while doing through the net. 

From a physical layer stand point, you are missing the communication bus. The communication bus will vary depending on the module that you are using but you'll typically find that they use two wire serial (TX/RX) or SPI (MISO/MOSI/CLK/CS). 
The serial interface is usually the easiest to setup with transfer rates of 115200 and AT commands are usually used to communicate with the chip. Alternatively, SPI can be used, which is usually a little more involved to setup but not much more but the transfer rates can be upwards of 4 Mbps. 

You still have not supplied enough information. Have you got a user manual for the Device that describes the function of it,  what inputs it expects,  what outputs are available at what data rate in what format and on what connector(s).If you can establish that data is available in an identifiable format, on a USB or Serial connector for example, then you can proceed from there. If not, then you are flying blind, and a lot of work would need to be done with a logic analyser to try and sort it out.Since you do not have access to the Device to reprogram it, you will need to further process the data.You will need a processor card that will have the capability of keeping up with the input data rate (you may have to throw some data away) with an appropriate input connector matching the output connector on the Device. It will need to take the  data from the Device , reformat it, and spit it out on an SPI bus or Serial bus (TTL RS232) that is likely available on your wireless card. The way this is done has already been briefly  described.
Note that your input data rate is also related to the capacity of the wireless card to accept data, there is a large overhead with some protocols, which will reduce the real data rate.Depending on your requirements, and programming skills, a Raspberry Pi, Arduino, or a Micrpython board may do what you want for example. There are plenty of other choices.Without further information, it is hard to know what else to suggest. If you are not in the EE business, then you need to say if what has been suggested makes some sense. If it doesn't, you may need to get an EE consultant in to look over the system. Otherwise it is going to mean a lot of reading and learning a batch of new skills, which will be good to have, but it takes time. Who manufacturers the Device, do they have any hardware supporting wireless communication,cheers,Richard