How To Install And Manage Apache Qpid
When it comes to sending and receiving messages between applications and processes, there are many solutions you can choose from. They all have their pros and cons, therefore the best thing to do is to cross-check your requirements and match them against various available solutions.
Apache Qpid is one of the open-source messaging systems that implements the Advanced Message Queuing Protocol (AMQP) to help you solve your needs of advanced messaging between different elements of your deployment stack.
Messaging, Message Brokers and Queues
Messaging is a way of exchanging certain data between processes, applications, and servers (virtual and physical). These messages exchanged, helping with certain engineering needs, can consist of anything from plain text messages to blobs of binary data serving to address different needs. For this to work, an interface managed by a third party program (a middleware) is needed - welcome Message Brokers.
Message Brokers are usually application stacks with dedicated pieces covering each stage of the exchange setup. From accepting a message to queuing it and delivering it to the requesting party, brokers handle the duty which would normally be much harder or cumbersome to do with non-dedicated solutions or simple hacks such as using a database, cron jobs, etc. They simply work by dealing with queues which technically constitute infinite buffers, to put messages and pop-and-deliver them later on to be processed either automatically or by polling.
Why use them?
These message brooking solutions act like a middleman for various services (e.g. your web application). They can be used to greatly reduce loads and delivery times by web application servers since tasks, which would normally take quite bit of time to process, can be delegated for a third party whose sole job is to perform them (i.e. workers). They also come in handy when a more "guaranteed" persistence is needed to pass information along from one place to another.
When to use them?
All put together, the core functionality explained expands to cover a multitude of areas, including-but-not-limited-to:
Allowing web servers to respond to requests quickly instead of being forced to perform resource-heavy procedures on the spot
Distributing a message to multiple recipients for consumption (i.e. processing)
Letting offline parties (e.g. a disconnected user) fetch data at a later time instead of having it lost permanently
Introducing fully asynchronous functionality to the backend systems
Ordering and prioritising tasks
Balancing loads between workers
Greatly increase reliability and uptime of your application
and much more.
Apache Software Foundation has several solutions when it comes to messaging and one of them is Apache Qpid: The foundation's implementation of AMQP. Unlike some more basic applications which are aimed at helping developers to craft their own solutions, Qpid, similar to RabbitMQ, offers a nice toolset capable of queuing, security and transaction management, clustering, persistence via a pluggable layer and more. Its API, by default, supports multiple programming languages and it comes with both C++ (for Perl, Python, Ruby, .NET etc.) and Java (JMS API) brokers. Alongside RabbitMQ, Qpid is probably the most popular choice.
How is it different than the others?
Message brokers which are fully fledged differ only slightly on the surface. However, a deeper look into internals reveal the truth behind how things work. The following are the features which make Apache Qpid stand out compared to others:
Client failover detection and automatic healing by connecting to a different broker
Easy clustering by replicating queues across different servers
Error handling by default in clusters
Easy persistence via a pluggable architecture to offer high-availability
Advanced Message Queuing Protocol (AMQP) in Brief
AMQP is a widely accepted open-source standard for distributing and transferring messages from a source to a destination. As a protocol and standard, it sets a common ground for various applications and message broker middlewares to interoperate without encountering issues caused by individually set design decisions.
Installing Apache Qpid
Getting started with Apache Qpid means installing two different sets of tools:
An implementation of Qpid Broker depending on programming language of your choice (e.g. C++ broker for Python or Java Broker for Java)
Qpid Client libraries (e.g. Qpid Python)
Note: We will be performing our installations and the actions listed here on a fresh and newly created droplet for various reasons. If you are actively serving clients and might have modified your system, to not to break anything working and to not to run in to issues, you are highly advised to try the following instructions on a new system.
Installing on CentOS 6 / RHEL Based Systems
Let's update our droplet:
yum -y update
And then let's run the following to get Qpid C++ Server and its tools (including Python bindings):
yum install -y qpid-cpp-server qpid-tools
If you require, continue installing Qpid's language bindings for others such as Ruby:
yum install -y ruby-qpid
Installing on Ubuntu 13 / Debian 7 Based Systems
The process for downloading and installing Apache Qpid on Ubuntu and Debian will be similar to CentOS.
Let's begin with updating our system's default application toolset:
apt-get update apt-get -y upgrade
And then let's run the following to get Qpid C++ Server and its tools:
apt-get install -y qpidd qpid-tools apt-get install -y libqpidmessaging2-dev python-qpid ruby-qpid
Note: During the installation process you will be prompted to enter a password of your choice for the Qpid daemon administrator.
Managing Apache Qpid
Managing on CentOS / RHEL Based Systems
To start, stop, restart, and check the application status, use the following:
# To start the service: /sbin/service qpidd start # To stop the service: /sbin/service qpidd stop # To restart the service: /sbin/service qpidd restart # To check the status: /sbin/service qpidd status # To force reload: /sbin/service qpidd force-reload
Managing on Ubuntu / Debian Based Systems
To start, stop, restart, and check the application status on Ubuntu and Debian, use the following:
# To start the service: service qpidd start # To stop the service: service qpidd stop # To restart the service: service qpidd restart # To check the status: service qpidd status # To force reload: service qpidd force-reload
And that's it! You now have your own Apache Qpid message broker working on your droplet.
Working with Apache Qpid
Following our installation of Qpid along with its Python language bindings, let's look into a simple Qpid example to understand basics of working with it.
Create a (sample)
hello_world.py file using
Paste the below self-explanatory module:
# Import the modules we need from qpid.messaging import * broker = "localhost:5672" address = "amq.topic" connection = Connection(broker) try: connection.open() # Define the session session = connection.session() # Define a sender *and* a receiver sender = session.sender(address) receiver = session.receiver(address) # Send a simple "Hello world!" message to the queue sender.send(Message("Hello world!")); # Fetch the next message in the queue message = receiver.fetch() # Output the message print message.content # Check with the server session.acknowledge() except MessagingError, err: print err finally: connection.close()
Press CTRL+X and confirm with Y to save and exit.
When you run the above script, you should see our message (i.e. Hello world!) as the output now.
python hello_world.py # Hello world!
If you run into an issue, be sure that qpid is running. You can start it using the commands above.