RabbitMQ by Example

Question 1

What is RabbitMQ?

Answer 1

It is a open-source messaging queue system.

Question 2

What protocol does RabbitMQ is based on?

Answer 2

AMQP protocol - which stands for advanced message queue protocol.

Question 3

What are the main features of RabbitMQ?

Answer 3

Reliability: messages can be persisted and even the server can be restarted. Also supports message delivery acknowledgement to ensure the message was received.
Routing: Uses exchanges to route the messages to the proper queues.
Clustering and High Availability: Many instances of rabbit MQ can act as one, which tolerate failures without loosing messages.
Management Web Interface: Default UI that comes with the rabbitMQ server.
Command line tool: Called RabbitMQ ctrl and admin - offer the same level of configuration as the web interface but here you can do scripting.

Question 4

Which languages have the rabbitMQ clients?

Answer 4

Pretty much all of them.

Question 5

What is AMQP?

Answer 5

Network protocol that enables applications to exchange messages to other clients via a server.

Question 6

What is MSMQ?

Answer 6

MSMQ was availablr to developers on 1997. ensure successful message delivery by placing failed messages on different queues. Also supports transactions.

Question 7

What is the difference between rabbitmq and MSMQ?

Answer 7

centralized and descentralized;
multi platform vs windows only;
standard based (AMQP) vs no standards;

Question 8

Which language was rabbitmq written on?

Answer 8

Erlang.

Question 9

What are some common functions of RabbitMQ?

Answer 9

Declare, list and delete rmq entities;
Queue and exchange monitoring;
Send and receive messages;
Monitor Erlang processes, file descriptors and memory use;
Force close connections, and purge queues.

Question 10

What is a binding?

Answer 10

It is the connection between the queue and the exchange.

Question 11

Where is the actual message stored?

Answer 11

In the Payload.

Question 12

What is the requeue concept?

Answer 12

When true it means that you’ll read the message and leave it in the queue, otherwise remove from the queue (similar to pm_pmnoremove)

Question 13

What is the common path a messages goes through until it gets to a consumer?

Answer 13

Publisher -> exchange -> routes -> Queue -> Consumer

Question 14

What happens when a message can’t get to a consumer? Is it configurable?

Answer 14

it is configurable, can be returned to the sender, dropped or placed on a different queue.

Question 15

What is a routing key?

Answer 15

Acts like a filter. It is a another way to filter further a message inside a queue.

Question 16

What are the different types of exchanges?

Answer 16

Direct exchanges: Based on message routing key;
Fanout exchanges: Post the message to all queues that are connected to it (a copy of the message is posted on all queues).
Topic Exchanges: Wild cards on routing key to be able to post the same message on different queues (which also might have wildcards).
Header Exchanges: Routing key is ignored and the header will contain the routing keys (might have many) which are customized (e.g: material = wood).

Question 17

What is an exchange? What does it do? What does it use to route stuff?

Answer 17

Exchanges are message routing agents, defined by the virtual host within RabbitMQ. An exchange is responsible for routing the messages to different queues with the help of header attributes, bindings, and routing keys. Take a message and route to one or more queues.

Question 18

What are the four attributes of an exchange?

Answer 18

Name: Name of the exchange;
Durability: Persisting the message to disk;
Auto-delete: Delete message when not needed
Arguments: These are message broker-dependent

Question 19

When the fanout exchange is ideal?

Answer 19

For broadcasts. E.g: sending a chat message to a group of people.

Question 20

What is a queue? Does it work in a li-fo mode?

Answer 20

Queue is where the messages are posted. Works in a first in first out basis.

Question 21

What are the additional properties the queues provides in extra to the exchange?

Answer 21

Name: name of the queue;
Durable: Persisting the queue to disk;
Exclusive: Exclusive to one connection. Delete queue when not needed;
Auto Delete: Queue deleted when consumer unsubscribes.

Question 22

What is the durable concept means in RabitMQ

Answer 22

Means it will survive if the server goes down.

Question 23

What happens when a queue is declared? What happens if it already exists?

Answer 23

The queue is created. When already created nothing happens.

Question 24

Do I need to define a queue name?

Answer 24

No… the broker can generate it automatically.

Question 25

What is the max length of a queue name?

Answer 25

255 characters.

Question 26

What happens when a message is published to a queue that does not exist?

Answer 26

Depends… might be returned to the sender.

Question 27

Can I have more than one subscriber to a queue? When is it used?

Answer 27

Yes. It is common when you want to scale your application out once one of the free consumers might get the message to do some processing.

Question 28

When a message is removed from the queue?

Answer 28

When the consumer receives the message or when the consumer receives the message AND acknowledges to the queue

Question 29

What happens when an application receives the message but fails to process it?

Answer 29

The message can be discarded or re-queued. The consumer decides.

Question 30

Where are the core client classes located in the .net rabbitmq client lib?

Answer 30

RabbitMQ.Client namespace.

Question 31

What are the common interfaces of .net rabbitmq client lib?

Answer 31

IModel: most AMQP operations;
IConnection: an AMQP connection;
ConnectionFactory: Creates IConstructor;
ConnectionParameters and QueueingBasicConsumer;

Question 32

What is necessary to connect to a RabbitMQ using .net rabbitmq client lib?

Answer 32

HostName, Username and password (default guest).

Question 33

How to create a channel to RabbitMQ using .net rabbitmq client lib?

Answer 33

by calling connection.CreateModel();

Question 34

What is necessary to be done before using the exchanges and queues when using .net rabbitmq client lib?

Answer 34

It is necessary to declare them (if the object does not exists, then it is created):
var channel = connection.CreateModel();
channel.ExchangeDeclare;
channel.QueueDeclare;
channel.QueueBind("myQ", "MyExchange", "");

Question 35

When the messages can be send when using .net rabbitmq client lib?

Answer 35

after the queue is bound.

Question 36

What is necessary to do to post an object to the queue when using .net rabbitmq client lib?

Answer 36

It is necessary to data annotate the object as [Serializable] in order to convert to byte array and then post in the queue.

Question 37

What to use to serialize objects when using .net rabbitmq client lib? Do we need a specific lib?

Answer 37

ObjectSerializer, can be found in the newtonsoft.json lib.

Question 38

How does a serialized object look like?

Answer 38

Like a json string which is then converted to bytearray.

Question 39

What happens when no exchange is defined in RabbitMQ when using .net rabbitmq client lib?

Answer 39

The message is posted to the default exchange.