Which messaging layer to use in a loosely coupled

distributed app?!

Narahari (Hari) Allamraju

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java developer; python enthusiast working with messaging systems for 9.5 years

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http://github.com/supercoderz anarahari@gmail.com1

• brief intro about work done • what to expect from this talk?

• a outline of what messaging is about and where it is used • how you should apply this to your situation and what to watch out for • advice based on experience from working on medium to large scale applications

Messeveryone talks to everyone

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• as the organisations grow, they build up a large number of IT systems performing different functions • sometimes it is not possible to throw away all the systems and build a more integrated solution for legacy reasons • sometimes the problem is just a question of improving efficiency • sometimes its about the best utilisation of legacy systems, resources and costs • these factors drive us to build connections between the applications. • there are many ways to do this - good and bad ways.

Messagingeveryone talks to everyone through a single medium

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• a properly designed messaging system lets the applications and components work with each other without getting in their way • its part of the architecture and is transparent enough that no one feels they need to do a lot of boiler plate extra work to get data across • its efficient and shows an improvement from the previous state of the system - you can tell that you are no longer doing time consuming manual work to ensure all systems see the same data. • and more importantly you should be able to see a consistent view of the entire organisation from any application - real time or a consistent view as of a given time.

Work Queueeveryone queues their tasks at the same place and waits

for the results4

• the other kind of use for messaging queues - more commonly seen today across all the web applications and user centric web applications is the work queue • these messaging systems follow the same logic as the ones that help connect all the systems in an organisations - help increase the efficiency without getting in the way or increasing work load.

So you want to build a loosely

coupled app!

why? do you know what side effects you will have?

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ok you know … !

what do you need to do?

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• why? • what do we get when we build a loosely coupled app - apart from the increase in efficiency?

• scalability • distributed load • reliability - since we know the flow and it is proven to work without manual intervention • ease of making changes

• it also adds a lot more moving parts :)

The basics• Will the application benefit by

splitting up into components?

• What are the components? How are they dependent on each other?

• Do we need more than one instance of each to cope up with the load?

• Do we need newer components to handle certain cases that arise from the new messaging layer?

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• just like everything else, you need to think out carefully about what you want - because once its built you don’t want to be in doubt about what you were expecting, and you should see the results • in some cases, splitting up work or adding a messaging layer can cause other unexpected issues

• case 1 : a file based data transfer was changed to a pseudo real time process through a message queue. however, this meant that in case the data had to be replayed or re-loaded in case of certain operational issues, it could not be done. this could have been solved by adding a record/replay component.

• case 2 : a consumer application was working slow, this caused the messages to pile up and trigger an alert for the support team due to disk/memory usage. while not a problem, this is an operational issue. •

Identify the patterns• What sort of interface do we

need - request-reply, publish subscribe or queuing?

• Do we need to separate out messages into various types?

• Do we need schemas for the messages or free form?

• Are there any components that have a higher or lower throughput than others?

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• its always good to know how the components you will integrate work - helps you to build in protections and handle unexpected corner cases • it also helps you to define the best architecture for your needs - this is important because if the architecture that you choose does not reflect the most common use cases, then you will not get the most out of your solution • it also helps you to determine the kind of setup you will need and the resources like storage etc

Latency, routing, priority• Which components need the

message yesterday; and which can wait till end of day?

• Do we need to expire messages when they are too late?

• How easily can we route messages?

• Can we make some messages take highest priority?

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• messages are always important and you can never lose one • but the application that consumes them can decide whether it wants all of the, or the last one or if it can afford to lose a message once in a while • sometimes it is even required to separate out the applications that consume messages slower into their own partitions in the architecture •

Build, Manage and Support

• Do we have a suitable API?

• Easy to provision and manage

• Good monitoring

• Guaranteed delivery of messages

• Should be persist messages to disk for crash recovery?

• Cleanup in case of issues

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• developers come first because like any application, they need to code an interface to the messaging layer from their existing application • also if they want to setup a developer environment, or a test instance - it should be very easy to do • support teams would love features that let them find issues faster • built in fail safe - pull the plug

A few options

• RabbitMQ

• ZeroMQ

• Redis

• RDBMS or NOSQL database

• RPC

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Considering future growth

• What if the loads increased by 15%?

• What if we had a consistent heavy run for 24 hours or more?

• Storage costs etc

• If we have to switch to a different underlying - how hard is it?

Tokyo Metro

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• this is something that actually happens on the train at peak hours • the best part of this - even with that rush, everyone understands, accommodates and everyone ensures that people get to where they need to get to - the whole system manages to handle that load, just at the limit and come out of it. almost 365 days a year.

Questions!• This presentation can be

found on slideshare at - http://goo.gl/KVJxoE !

• The version with speaker notes will be available soon !

• you can also email me at anarahari@gmail.com

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