ACA project

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# Using MQTT to modify extra-functional requirements in adaptive applications
## Advanced Computer Architectures Project
## Politecnico di Milano, 2017
.footnote[Marco Ieni]
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## Project goal

Develop a sender and a receiver that talk with each other through the MQTT protocol.

* the receiver is an adaptive application, that runs the mARGOt library and has to communicate his own goals and states to the sender.

* the sender has to send to the receiver the new values of goals and states, in order to modify the objective functions.

Example: Communicate to a device to switch from a low-power mode to an high performance state.
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# Scenario
.center[![Scenario](images/scenario.png)]

???

we have different senders that can send goals or states to adaptive applications through a terminal.
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# Let's analyze each component
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.left-column[
  ## MQTT Broker
]
.right-column[
It is enough the mosquitto broker used with its default configuration.
]
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.left-column[
## MQTT Broker
## Sender
]
.right-column[
* written in python.

* the networking part depends on the library paho-mqtt and all the messages sent and received are saved in a log file.

* it saves the states and the goals that the receivers signal to him, so before sending something it checks its validity.

* it has a shell based on the cmd library, that implements the following commands:

- info: get info about a single receiver using his hostname.

- list: get info about all the receivers.

- set_goal: change the value of a goal in a receiver.

- set_state: change the active state in a receiver.
]
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.left-column[
## MQTT Broker
## Sender
## Receiver
]
.right-column[
* written in C++.

* the networking part depends on the library paho-mqtt.

* it interacts with the mARGOt library to modify the objective function of the adaptive application.

* it is characterized by the following hierarchical structure: hostname/pid/app/block.

* The receiver project is divided in three parts:
  - mqtt_receiver: the core library that you can integrate in your mARGOt adaptive app.

- gs_list: a wrapper library that tells to the mqtt_receiver what goals and states are declared.

- margot: this is an example on how to integrate the mqtt_receiver library in a mARGOt adaptive application.
]
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# How does it work?
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## Goals

<!---
I tried to embed this sequence diagram with mermaid, but since I see rendering
problem when I switch between pages I prefer to attach directly the image,
however I report the correspondent code anyway.

"#35;" stands for "#"

<div class="mermaid">
sequenceDiagram
    participant Sender
    participant Broker
    Sender->>Broker: sub("client/#35;")
    Note right of Receiver: Add "cpu" goal
    Receiver->>Broker: sub("sender/receiver1/18432/app1/block1/goal/cpu")
    Receiver->>Broker: pub("client/receiver1/18432/app1/block1/goal", "cpu")
    Broker->>Sender: publish forward
    Sender->>Sender: add_goal("cpu")
    Note left of Sender: I want to change<br/>"cpu" to 60%
    Sender->>Broker: pub("sender/receiver1/18432/app1/block1/goal/cpu", 60)
    Broker->>Receiver: publish forward
    Receiver->>Receiver: margot::block1::goal::cpu.set(60);
</div>
--->

.center[![Goals sequence diagram](images/seq_goals.png)]
---

## States

"#35;" stands for "#", while "#059;" stands for ";"

<div class="mermaid">
sequenceDiagram
    participant Sender
    participant Broker
    Sender->>Broker: sub("client/#35;")
    Note right of Receiver: Add "performance" state,<br/> with domain: ["high","low"]
    Receiver->>Broker: sub("sender/receiver1/18432/app1/block1/state/performance")
    Receiver->>Broker: pub("client/receiver1/18432/app1/block1/state", "performance#059;high#059;low")
    Broker->>Sender: publish forward
    Sender->>Sender: add_state("performance", ["high","low"])
    Note left of Sender: I want to change "performance" to "low"
    Sender->>Broker: pub("sender/receiver1/18432/app1/block1/state/performance", "low")
    Broker->>Receiver: publish forward
    Receiver->>Receiver: margot::block1::manager.change_active_state("low")
</div>
--->

.center[![States sequence diagram](images/seq_states.png)]

???

What if the sender is not yet up (or is not yet registered to the topic "client/#") when the receiver wants to register a goal or a state?
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## Disconnection
* When a receiver is disconnected, it publishes a message on the topic "client/disconnect/hostname".

* The same topic is set as Last Will Topic. In this way, when the broker detects that a receiver is not active anymore, it sends the
disconnect message to the sender.

* Therefore, even in the case of a hard disconnection, the sender can detect that a receiver is no more
active and so, it will allow to send messages only to the receivers that are currently active.
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## Retained Messages
* What if a sender is connected to the system after that the receiver sends a goal or a state?

* We want that all the senders are able to see all goals and states of the receivers that are on.

* In order to satisfy this requirement, all the messages (including the disconnect ones) sent from the receivers are **retained**.

* When a disconnect message is received, the sender deletes all the retained messages sent by that client by sending an empty message to the topics of the retained messages.

* In this way, when a sender is connected, it will receive all the messages sent from the receivers that are not yet disconnected.
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# Shell interaction example
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## Set Goal Example
```terminal
mieni@ubuntu:~$ python shell.py
Welcome to the sender shell.   Type help or ? to list commands.

>> help

Documented commands (type help <topic>):
========================================
exit  help  info  list  set_goal  set_state

>> help list
Get the data of all the clients:  list
>> list
ubuntu
	43414
		app1
			foo - goals: set(['my_execution_time_goal', 'my_error_goal']) - states
: set([{'domain': ['my_state_minimize_error', 'my_state_minimize_exec_time']
, 'name': 'my_state'}])
	43421
		app1
			foo - goals: set(['my_execution_time_goal', 'my_error_goal']) - states
: set([{'domain': ['my_state_minimize_error', 'my_state_minimize_exec_time']
, 'name': 'my_state'}])

>> set_goal ubuntu 43414 foo my_error_goal 0.6
*** invalid number of arguments
>> set_goal ubuntu 43414 app1 foo my_error_goal 0.6
>>
```
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## Shell features
* command history like a normal linux terminal.

* command validity checks.

* hierarchical view of receiver hostname/pid/app/block. For example in this case we have two process
(obviously with different pids) that runs on the same client named "ubuntu".
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## Thank you for the attention!
GitHub repo: https://github.com/MarcoIeni/aca_project
.footnote[Slideshow created using [remark](http://github.com/gnab/remark).]