Synchronous and asynchronous software communication components allow applications to exchange information. Synchronous components like REST APIs use requests and responses over HTTP to transfer data immediately. Asynchronous message queues decouple systems by allowing producers to send messages without waiting for consumers to process them, improving scalability. Messages in queues can be retrieved when consumers are ready. Real-world examples of asynchronous communication include email and job processing queues that separate workloads across independent systems.

1. SYNCHRONOUS &
ASYNCHRONOUS SOFTWARE
COMMUNICATION COMPONENTS
Panos Tsilopoulos
Full stack software engineer @
Pheron
Email:
pan_tsilopoulos@outlook.com
Social media handle:
@tsilopoulos

2. SYNCHRONOUS
COMMUNICATIONS
SOFTWARE COMPONENTS
REST

3. Definitions & Core
Principal
What does it stand for?:
REpresentational State Transfer
What Is it?
It’s a way of providing interoperability between computer systems
over the Internet
Who/Where/When?
Resources:
Data, files,
methods
Where:
URL
based
How:
HTTP
What:
Up to
you

4. WHERE/HOW: A SIMPLE
EXAMPLE URLs
Premise:
• Data in a table could be a resource we want to read
• Database server called bbddb01
• Database called northwind
• Table called users
http://bbddb01/northwind/users

5. THE WHAT: DATA, DATA,
DATA JSON
What type of content you return is up
to you.
Most common are XML or JSON.
You could return complex types like a
picture.
“JSON (JavaScript Object Notation) is a lightweight
data-interchange format. It is easy for humans to
read and write. It is easy for machines to parse and
generate” – JSON.org
Important: JSON is a subset of JavaScript
{
"firstName": "John",
"lastName": "Smith",
"address": {
"streetAddress": "21 2nd Street",
"city": "New York",
"state": "NY",
"postalCode": 10021
},
"phoneNumbers": [
"212 555-1234",
"646 555-4567"
]
}
String
Array
Number data
type
Child
properti
es
Name/Value
Pairs

6. DATA STRUCTURES JSON

7. A REAL LIFE EXAMPLE: FLICKR
REST API
Resource: Photos
Where:
 http://farm{farm-id}.static.flickr.com/{server-id}/{id}_{secret}.jpg
 http://farm{farm-id}.static.flickr.com/{server-id}/{id}_{secret}_[mstb].jpg
 http://farm{farm-id}.static.flickr.com/{server-id}/{id}_{o-
secret}_o.(jpg|gif|png)
What: JPEG, GIF or PNG (defined in the URL)
http://farm1.static.flickr.com/2/1418878_1e92283336_m.jpg

8. METHODS REST

9. VERB
S
HTTP Methods are a key corner stone in REST.
They define the action to be taken with a URL.
Proper RESTful services expose all four – usually not the case though!
Google “RESTafarian” for more information on that debate.
Nothing stopping you doing some Mix & Match, especially when you’re time
constrained & don’t really wanna think the details through, like a Hackathon!
Build a working MVP(Minimum Viable Product) and worry about the
implementation details later!
What are the four methods and what should they do?

10. METHODS EXAMPLE
VERB
S
+ POST = Error
+ GET = Returns everyone who begins
with rob
+ PUT = Error
+ DELETE = Deletes everyone who begins
with rob
http://bbddb01/northwind/users
plus some input data
+ POST = Creates a new user
+ GET = Returns everyone who meets
criteria
+ PUT = Creates/Updates a user (based on
data)
+ DELETE = Deletes everyone who meets
criteria
http://bbddb01/northwind/users[firstname=“
rob%”]

11. COMMANDS REST

12. You can associate commands with a resource.
Commands can replace the need for using HTTP
methods and can provide a more familiar way of
dealing with data.
Example:
userResource = new
Resource('http://example.com/users/001')
userResource.delete()

13. ASYNCHRONOUS
COMMUNICATIONS
SOFTWARE COMPONENTS
MESSAGE
QUEUES

14. DEFINITIONS
Message queuing allow applications to communicate by sending messages to each other.
The message queue provide a temporary message storage when the destination program is busy or
not connected.
A queue is a line of things waiting to be handled - in sequential order starting at the beginning of the line.
A message queue is a queue of messages sent between applications. It includes a sequence of work objects
that are waiting to be processed.
A message is the data transported between the sender and the receiver application, it's essentially a byte
array with some headers on top. A message example could be anything that tells one system to start
processing a task, information about a finished task or a plain message.
The basic architecture of a message queue is simple, there are client applications called producers that
create messages and deliver them to the message queue. An other application, called consumer, connect to
the queue and get the messages to be processed. Messages placed onto the queue are stored until the
consumer retrieves them.
MESSAG
E
QUEUES

15. WHY SHOULD WE BE
INTERESTED IN MESSAGE
QUEUES? PT.1
Message queues
A message queue provide an asynchronous communications protocol, a system that puts a message onto a
message queue does not require an immediate response to continue processing. Email is probably the best
example of asynchronous messaging. When an email is sent can the sender continue processing other things
without an immediate response from the receiver. This way of handling messages decouple the producer from
the consumer. The producer and the consumer of the message do not need to interact with the message queue
at the same time.
DECOUPLING AND SCALABILITY
Decoupling is used to describe how much one piece of a system relies on another piece of the system.
Decoupling is the process of separating them so that their functionality will be more self contained.
A decoupled system are achieved when two or more systems are able to communicate without being connected.
The systems can remain completely autonomous and unaware of each other. Decoupling is often a sign of a
computer system that is well structured. It is usually easier to maintain, extend and debug.
If one process in a decoupled system fails processing messages from the queue, other messages can still be
added to the queue and be processed when the system has recovered. You can also use a message queue to
delay processing; A producer post messages to a queue. At the appointed time, the receivers are started up and
process the messages in the queue. Messages in queue can be stored-and-forwarded and the message be
redelivered until the message is processed.
MESSAG
E
QUEUES

16. WHY SHOULD WE BE
INTERESTED IN MESSAGE
QUEUES? PT.2
MESSAG
E
QUEUES
Instead of building one large application, is it beneficial to
decouple different parts of your application and only
communicate between them asynchronously with
messages. That way different parts of your application can
evolve independently, be written in different languages
and/or maintained by separated developer teams.
A message queue will keep the processes in your application separated and independent of each other. The first
process will never need to invoke another process, or post notifications to another process, or follow the process flow
of the other processes. It can just put the message on the queue and then continue processing. The other processes
can also handle their work independently. They can take the messages from the queue when they are able to process
them. This way of handling messages creates a system that is easy to maintain and easy to scale.

17. MESSAGE QUEUING - A
SIMPLE USE CASE
MESSAG
E
QUEUES
Imagine that you have a web service that receives many requests every second, where no request is afford to get lost
and all requests needs to be processed by a process that is time consuming.
Imagine that your web service always has to be highly available and ready to receive new request instead of being
locked by the processing of previous received requests. In this case it is ideal to put a queue between the web service
and the processing service. The web service can put the "start processing"-message on a queue and the other
process can take and handle messages in order. The two processes will be decoupled from each other and does not
need to wait for each other. If you have a lot of requests coming in a short amount of time, the processing system will
be able to process them all anyway. The queue will persist requests if their number becomes really huge.
You can then imagine that your business and your workload is growing and you need to scale up your
system. All that is needed to be done now is to add more workers, receivers, to work off the queues faster.

18. A REAL LIFE EXAMPLE:
HIRENAMI’S PUBLISH-
SUBSCRIBE PATTERN
COMMS

19. LIVE CODING SESSION UNDER WAY

20. REFERENCES & FURTHER
STUDYING MATERIAL
• Hypertext Transfer Protocol – HTTP/1.1 https://tools.ietf.org/html/rfc2616
• Introducing JSON - http://json.org/
• FLICKR Developer Services https://www.flickr.com/services/developer/api/
• Publish-Subscribe pattern – Wikipedia
https://en.wikipedia.org/wiki/Publish%E2%80%93subscribe_pattern
• Amazon Web Services (AWS) Simple Queue Service (SQS)
https://aws.amazon.com/sqs/details/

21. THANKS FOR
ATTENDING!