Azure tales: a real world CQRS and ES Deep Dive - Andrea Saltarello

@ITCAMPRO #ITCAMP17Community Conference for IT Professionals
Azure tales: a real world CQRS and
ES Deep Dive
Andrea Saltarello
Solution Architect @ Managed Designs
https://twitter.com/andysal74
https://github.com/andysal

Many thanks to our sponsors & partners!
GOLD
SILVER
PARTNERS
PLATINUM
POWERED BY

Andrea Saltarello
• Solution Architect @ Managed
Designs
• Microsoft .NET MVP since 2003
• Microsoft Regional Director
• Author, along with Dino, of .NET:
Architecting Applications for the
Enterprise, di Microsoft Press
• Basically, a software architect eager
to write code ☺

• CQRS/Event Sourcing recap
• CQRS/ES @ Azure: deployment blueprints
• Technology & economic considerations
Agenda

CQRS/ES RECAP

Not the way to implement Event Sourcing, but a
working way to do it nonetheless
Demo app available on Github (GPL3): it is a real open
source project of which my company sells
customizations
There’s no silver bullet

A few fancy dressed blokes going for a jaunt
The (Relational) Lord of the Rings

It really became clear to me in the last couple of years that we
need a new building block and that is the Domain Event.
[Eric Evans]
An event is something that has happened in the past.
[Greg Young]
A domain event … captures the memory of something
interesting which affects the domain
[Martin Fowler]

Instead of focusing on a system’s last known
state, we might note down every occurring
event: this way, we would be able to (re)build
the state the system was in at any point in time
just replaying those events
To cut a long story short: we’d end up
recording an event stream
Event Sourcing in a nutshell
JobOrderStarted InvoiceIssuedJobOrderExtended JobOrderCompleted

The (immutable) composition of:
• A (meaningful) name
• (Typed) Attributes
What’s an event, anyway?
InvoiceIssued
DateOfIssue
Customer
Price
ProjectStarted
DateOfStart
ProjectId
ProjectCompleted
DateOfCompletion
ProjectId
ProjectRegistered
DateOfRegistration
DateOfEstimatedCompletion
ProjectId
CustomerId
Price

DEMO
Event Stream

Still, my users are more interested in knowing a job
order’s balance or whether an invoice has been paid.
(cit.)
That is, we need a way to produce an entity state
Event Stream vs. «My application»

DDD’s Aggregates provide a convenient way to encapsulate event
management
Aggregate: A collection of objects that are bound together by a root
entity, otherwise known as an aggregate root. The aggregate root
guarantees the consistency of changes being made within the
aggregate.
[Wikipedia]
An aggregate is responsible for:
• encapsulating business logic pertaining to an “entity”
• generating events to have them available for saving
• replaying events in order to rebuild a specific state
Event Sourcing <3 DDD

DEMO
Aggregates

var aggr = repository.GetById<TAggr>(id); //Triggers [time travelling] event
replay
aggr.DoSomething(); //Biz logic + events
repository.Save(aggr); //Updates the event stream
Repository: Mediates between the domain and data mapping layers using a
collection-like interface for accessing domain objects. [DDD]
Aggregates vs. Events vs. Repos

DEMO
Time Travelling

Still², my users are more interested in knowing a job
order’s balance or whether an invoice has been paid.
Quickly.
Ways to achieve that:
• Snapshots can help
• CQRS to the rescue: let’s have a database storing the usual «last
known system state» and use it as a read model
Event Stream vs. «My application»

Acronym for Command Query Responsibility
Segregation
Basically, ad hoc application stacks for either “writing”
or reading:
• “Command” stack writes events and snapshots
• “Read” stack reads from eventually consistent, reading
purposes optimized database(s)
Enter CQRS

DEMO
Read Model

1. Application sends a command to the system
2. Command execution might alter the system’s state and
then raise events to state success/failure
3. Events are notified to interested subscribers (a.k.a.
handlers), such as:
• Workflow managers (a.k.a. «Sagas») which could execute more
commands
• Denormalizers, which will update the read model database
Note: command/event dispatch/execution will usually be
managed by a Mediator («bus»)
CQRS/ES in a nutshell

Application
Layer
Snapshots
Event store
Read stack
Domain Layer
Ad-hoc DBHandlers
Command Event Data
Handlers
Model ServicesB
U
S
CQRS/ES at a glance

DEMO
Handlers

BLUEPRINTS

Azure <3 CQRS: n-tiered
Back-endFront-end
Application
Layer
Snapshots
Event store
Read stack
Domain Layer
Ad-hoc DBHandlers
Command Event Data
Handlers
Model Services
A
S
B

Front end:
• VM
• Web role
• App Service
• Docker
Back end:
• Worker role
• Service Fabric
• Docker
N-tiered deploy

Azure <3 CQRS: full stack
App Service
Application
Layer
Snapshots
Event store
Read stack
Domain Layer
Ad-hoc DBHandlers
Command Event Data
Handlers
Model Services
A
S
B

• VM
• Web role
• App Service
• Docker
• Service Fabric
Full stack deploy

A fine-grained deploy allows each “component” to be:
• Evolved
• Deployed
• Configured (e.g.: scaled)
Independently, thus having each one only consuming
the resources it really needs but it means having more
moving parts to manage
N-tiered vs. Full stack

TECHNOLOGY & ECONOMIC
CONSIDERATIONS

App Service Cloud Services Docker Service Fabric VM
PROs:
• PaaS
PROs:
• PaaS
PROs
• Deploy
• Scaling*
• Documentation/samples
PROs:
• Fault tolerance
• Load balancing
• Deploy
PROs
• (Usually) cheapest
monthly bill
• No new skiils needed
• Unparalled option set
CONs:
• .NET 4.5.1 only(*)
CONs: (?)
• Need for an orchestrator
CONs:
• Ad-hoc SDK
CONs:
• Management
Azure Compute smackdown

A 2 cores, 3.5 GB RAM, 60 GB disk compute unit costs:
• 75,92 EUR/month as a VM
• 94,11 EUR/month as an AppService
• 100,39 EUR/month as a Cloud Service (*)
• 338,80** - 564,47*** EUR/month as a Service Fabric
cluster
* 490Gb disk
**3 nodes
***5 nodes
From a billing perspective

An effective CQRS/ES implementation usually relies on
2 structural pillars:
• A mediator bus
• An event store
Well come on and let me know…
Should I stay build or should I go (shopping)? (demi
quote)
On a technology side…

Rebus.net:
• is an open source, production tested bus for .NET. Source code is available
on Github, but usually Nuget packages will do.
• provides much-needed features such as:
– Fault tolerance
– Scalability
– Events’ scheduling
– Easy migration from on-premises to cloud
• requires:
– a transport protocol (e.g.: MSMQ, RabbitMQ, Azure Service Bus, Amazon Sqs, ...)
– an IoC container (e.g.: Autofac, Ninject, .NET Core ServiceProvider, StructureMap,
Unity, Windsor...)
– a storage (e.g.: MongoDB, RavenDb, SQL Server, ...)
Enter Rebus.net

DEMO
Configuration
Back to the Future

MementoFX NEventStore
https://www.nuget.org/packages?q=MementoFx
• FOSS
• DDD/ES stack
• Time travelling
• Alternative timelines
https://www.nuget.org/packages?q=NEventStore
• FOSS
• Event Store API only
• “CommonDomain” package available to support DDD
• Wide community + Slack channel
CQRS Application Frameworks

CosmosDB mLab VM
PROS:
• Multiple APIs (e.g.: DocumentDB,
MongoDB)
• PaaS
• Scalability/Georedundancy
PROS:
• PaaS
• Large ecosystem
PROS:
• Unparalleled configuration
options
CONS:
• Billing
CONS:
• Few instance sizes
CONS:
• Management
Event Store: a couple of options

• A CosmosDB database is billed on a per-collection basis, with
a 1 GB, 400 RU/sec collection costing 20.08 EUR/month
• A 3 “A2” VM MongoDB Linux cluster costs 146,82 EUR/month
(but we’d have to manage it)
• mLab’s dedicated cluster options:
From a Billing perspective
Size RAM Disk Monthly price
M1 1.7 GB 40 GB $200
M2 3.5 GB 60 GB $400
M3 7 GB 120 GB $800
M4 14 GB 240 GB $1,320
M5 28 GB 480 GB $2,450
M6 56 GB 700 GB $4,280

THANK YOU!

Q & A

Azure tales: a real world CQRS and ES Deep Dive - Andrea Saltarello

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