Watch your communication How communication drives design Uwe - - PowerPoint PPT Presentation

Watch your communication

How communication drives design

Uwe Friedrichsen (codecentric AG) – GOTO Berlin – Berlin, 13. November 2016

@ufried

Uwe Friedrichsen | uwe.friedrichsen@codecentric.de | http://slideshare.net/ufried | http://ufried.tumblr.com

The “one-size-fits-all” trap

Standardization as a virtue

We see that a lot

• One programming language
• One framework
• One build system
• One type of runtime unit
• One data store
• One type of database access
• One application server
• One ...
• One communication paradigm

Why are we doing it?

Reducing complexity

• Avoid intellectual overload
• Easier to understand
• Easier to change
• Faster to change
• Easier to operate
• Less error-prone
• Cheaper

These are valid and important reasons …

... but that is just one side of the coin

The complexity of a solution
 must match
 the complexity of the problem to solve

If your task is to build a box from pre-cut boards,


• nly using a hammer might be adequate

If your task is also to paint the box you just built,


• nly having a hammer might be a problem …

Now imagine building a whole house
 just with a hammer …

Yet, in IT we often tend to build whole houses
 just with a hammer because boxes can be built with a hammer

Complexity mismatch means

• Increased accidental complexity
• Harder to understand
• Harder to change
• Slower to change
• Harder to operate
• More error-prone
• More expensive

Complexity

Essential complexity Adds direct accidental complexity

Problem complexity Ideal solution complexity

Adds indirect accidental complexity

Complexity

Problem complexity Overly complex solution

Increased accidental complexity

More “tooling” than needed to get the job done well

Complexity

Problem complexity Over- simplified solution

Increased accidental complexity

Not enough “tooling” to get the job done well

Overall Solution Complexity := Essential Problem Complexity + Solution Complexity Mismatch

Solution Complexity Mismatch a.k.a. Accidental Complexity Be aware that mismatch in both directions
 adds to overall solution complexity

Complexity

Essential complexity

Problem complexity

Aim for the least complex solution


with respect to the problem you have to solve

(Yes, it is about trade-offs – as always in architecture)

Communication paradigms

Communication paradigms

• Dimensions of communication
• Synchronous vs. asynchronous
• Request/response vs. message passing
• Commands, Events and Documents
• Sender/Receiver dependency

Communication paradigms

• Typical communication patterns
• Synchronous request/response
• Asynchronous commands


(with known receiver)

• Asynchronous events


(without known receiver)

The “synchronous request/response everywhere” trap

Why are we doing it?

Remember the “one-size-fits-all” trap?

Yes, but why this paradigm?

Why synchronous R/R?

• “It’s how the internet works”
• “The library support is better”
• “It is easier to reason about”
• Matches the way we consciously think
• Matches the way we learned to do design

Do not forget the other side of the coin

The flipside of the coin

• HTTP was designed for a specific use case
• Access hypermedia content
• Not an ubiquitous communication solution
• The world outside a process is different
• Non-determinism kills easy reasoning
• Latency creep kills easy reasoning
• Solution mismatch adds complexity
• Compromises functional encapsulation
• Changes and extensions become more complicated
• Longer activation paths compromise robustness

Designing communication

An (invidious) example …

Order fulfillment

Let us begin with the well-known
 synchronous request/response design ...

Order fulfillment

Initial version with limited functionality


• Order includes
• Items
• Amounts
• Price per item
• T
• tal price
• Credit card payment
• Only non-digital items

Order Fulfillment
 Service Online Shop Payment
 Service Credit Card Provider Shipment
 Service Warehouse System

Order fulfillment

Add coupons


• Order additionally includes
• Optional coupon ID
• Optional remaining coupon value
• Coupon is already charged against total price
• Validate coupon

Order Fulfillment
 Service Online Shop Payment
 Service Shipment
 Service Warehouse System

Coupon Management

Credit Card Provider

Order fulfillment

Add promotions


• Order additionally includes
• Optional promotion ID
• Promotion is already applied to order
• Notify Campaign Management System

about promotion usage

Order Fulfillment
 Service Online Shop Payment
 Service Shipment
 Service Warehouse System

Coupon Management

Campaign Management

Credit Card Provider

Order fulfillment

Add customer accounts


• Order additionally includes
• Payment type (Credit card/Account)
• Charge customer account

Order Fulfillment
 Service Online Shop Payment
 Service Shipment
 Service Warehouse System

Coupon Management Campaign Management Account service Accounts Receivables

Credit Card Provider

Order fulfillment

Add PayPal


• Order additionally includes
• More payment types (Credit card/PayPal/Account)
• Payment via PayPal

Order Fulfillment
 Service Online Shop Payment
 Service Credit Card Provider Shipment
 Service Warehouse System

Coupon Management

Campaign Management Account service Payment provider PayPal Accounts Receivables

Order fulfillment

Add digital music library


• New shipment method
• Activate music assets in digital music library
• Notify customer via email including access link
• Digital music library has its own API

Order Fulfillment
 Service Online Shop Payment
 Service Credit Card Provider Shipment
 Service Warehouse System

Coupon Management

Campaign Management Account service Payment provider PayPal Accounts Receivables Music Library E-Mail Server

Order fulfillment

Add digital video library


• New digital shipment channel
• Activate video assets in digital video library
• Notify customer via email including access link
• Digital video library has its own API
• Different from the music library API

Order Fulfillment
 Service Online Shop Payment
 Service Credit Card Provider Shipment
 Service Warehouse System

Coupon Management

Campaign Management Account service Payment provider PayPal Accounts Receivables Music Library Video Library E-Mail Server

Order fulfillment

Add e-book library


• New digital shipment channel
• Activate e-books in e-book library
• Notify customer via email including access link
• E-Book library has its own API
• Different from the other asset library APIs

Order Fulfillment
 Service Online Shop Payment
 Service Credit Card Provider Shipment
 Service Warehouse System

Coupon Management

Campaign Management Account service Payment provider PayPal Accounts Receivables Music Library E-Book Library Video Library E-Mail Server

Order fulfillment

Add bonus card


• Order additionally includes
• Optional bonus card ID
• Potential discount is already applied to order
• Notify Loyalty Management System about

customer purchase

Order Fulfillment
 Service Online Shop Payment
 Service Credit Card Provider Shipment
 Service Warehouse System

Coupon Management

Campaign Management

Account service Payment provider PayPal Loyalty Management Accounts Receivables Music Library E-Book Library Video Library E-Mail Server

Order fulfillment

More requirements to come …

Order Fulfillment
 Service Online Shop Payment
 Service Credit Card Provider Shipment
 Service Warehouse System

Coupon Management

Campaign Management

Account service Payment provider PayPal Loyalty Management Accounts Receivables Music Library E-Book Library Video Library E-Mail Server

Synchronous request/response – findings

“Divide and conquer” design

• Tight service coupling
• including cross-domain coupling
• Long activation paths
• Latency creep
• Availability erosion
• Underlying design assumption is 100% availability of all services used
• Complex orchestration logic in services
• including cross-service transactions
• New downstream services require changes of upstream services
• including knowledge about how to access downstream services in upstream services

Let us repeat the design
 using asynchronous events ...

Order fulfillment

Order fulfillment

Initial version with limited functionality


• Order includes
• Items
• Amounts
• Price per item
• T
• tal price
• Credit card payment
• Only non-digital items

Order confirmed Online Shop Credit Card Provider Warehouse System

Credit Card Service Warehouse Service Payment authorized

Payment failed

Order fulfillment

Add coupons


• Order additionally includes
• Optional coupon ID
• Optional remaining coupon value
• Coupon is already charged against total price
• Validate coupon

Order confirmed Online Shop Credit Card Provider Warehouse System

Credit Card Service Warehouse Service Payment authorized

Payment failed Coupon Management Coupon Service

Order fulfillment

Add promotions


• Order additionally includes
• Optional promotion ID
• Promotion is already applied to order
• Notify Campaign Management System

about promotion usage

Order confirmed Online Shop Credit Card Provider Warehouse System

Coupon Management Campaign Management Credit Card Service Warehouse Service Promotion Service Coupon Service Payment authorized

Payment failed

Order fulfillment

Add customer accounts


• Order additionally includes
• Payment type (Credit card/Account)
• Charge customer account

Order confirmed Online Shop Credit Card Provider Warehouse System

Coupon Management Campaign Management Account service Credit Card Service Accounts Receivables Warehouse Service Promotion Service Coupon Service Payment authorized Payment failed

Order fulfillment

Add PayPal


• Order additionally includes
• More payment types (Credit card/PayPal/Account)
• Payment via PayPal

Order confirmed Online Shop Credit Card Provider Warehouse System

Coupon Management Campaign Management Account service Credit Card Service Accounts Receivables PayPal PayPal Service Warehouse Service Promotion Service Coupon Service Payment authorized Payment failed

Order fulfillment

Add digital music library


• New shipment method
• Activate music assets in digital music library
• Notify customer via email including access link
• Digital music library has its own API

Order confirmed Online Shop Credit Card Provider Warehouse System

Coupon Management Campaign Management Account service Credit Card Service Accounts Receivables Music Library E-Mail Server PayPal PayPal Service Warehouse Service Promotion Service Coupon Service Music Library Service Notification Service Payment authorized Digital asset provisioned Payment failed

Order fulfillment

Add digital video library


• New digital shipment channel
• Activate video assets in digital video library
• Notify customer via email including access link
• Digital video library has its own API
• Different from the music library API

Order confirmed Online Shop Credit Card Provider Warehouse System

Coupon Management Campaign Management Account service Credit Card Service Accounts Receivables Music Library Video Library E-Mail Server PayPal PayPal Service Warehouse Service Promotion Service Coupon Service Music Library Service Video Library Service Notification Service Payment authorized Digital asset provisioned Payment failed

Order fulfillment

Add e-book library


• New digital shipment channel
• Activate e-books in e-book library
• Notify customer via email including access link
• E-Book library has its own API
• Different from the other asset library APIs

Order confirmed Online Shop Credit Card Provider Warehouse System

Coupon Management Campaign Management Account service Credit Card Service Accounts Receivables Music Library E-Book Library Video Library E-Mail Server PayPal PayPal Service Warehouse Service Promotion Service Coupon Service Music Library Service Video Library Service E-Book Library Service Notification Service Payment authorized Digital asset provisioned Payment failed

Order fulfillment

Add bonus card


• Order additionally includes
• Optional bonus card ID
• Promotion is already applied to order
• Notify Loyalty Management System about

customer purchase

Order confirmed Online Shop Credit Card Provider Warehouse System

Coupon Management Campaign Management Account service Credit Card Service Loyalty Management Accounts Receivables Music Library E-Book Library Video Library E-Mail Server PayPal PayPal Service Warehouse Service Promotion Service Bonus Card Service Coupon Service Music Library Service Video Library Service E-Book Library Service Notification Service Payment authorized Digital asset provisioned Payment failed

And how do we figure out if a business transaction eventually completes?

Order confirmed Online Shop Credit Card Provider Warehouse System

Coupon Management Campaign Management Account service Credit Card Service Loyalty Management Accounts Receivables Music Library E-Book Library Video Library E-Mail Server PayPal PayPal Service Warehouse Service Promotion Service Bonus Card Service Coupon Service Music Library Service Video Library Service E-Book Library Service Notification Service Order fulfillment supervisor Payment authorized Digital asset provisioned Payment failed

• r fail for good, usually incorporating a

Order confirmed Online Shop Credit Card Provider Warehouse System

Coupon Management Campaign Management Account service Credit Card Service Loyalty Management Accounts Receivables Music Library E-Book Library Video Library E-Mail Server PayPal PayPal Service Warehouse Service Promotion Service Bonus Card Service Coupon Service Music Library Service Video Library Service E-Book Library Service Notification Service Payment authorized Digital asset provisioned Payment failed

Order fulfillment supervisor

• r fail for good, usually incorporating a

Asynchronous events – findings

“Go with the flow” design

• Services and domains decoupled
• Very short activation paths
• High responsiveness
• High availability
• No design assumptions about availability of services
• Coordination via choreography
• No central coordination and cross-service transactions
• Instead functional compensation logic in external supervision service
• New services can be integrated without touching existing services
• Services only focus on their task (no knowledge about other services required)

Didn’t we miss any special cases that
 would lead to very different findings?

Some special cases

Synchronous request/response design

• Current order status
• E.g., pass status through call chain
• Maybe additionally extend order fulfillment service

to store status in an status information database

• Payment failed
• E.g., stop processing in fulfillment service and send

back appropriate status to online shop

• Cashing coupon failed
• E.g., extend payment service to place task in desk
• fficer’s inbox
• Integrate new video library (different API)
• Adapt shipment service to new API
• Make sure not to disrupt other service aspects

Some special cases

Asynchronous events design

• Current order status
• E.g., track events with a new service and store


them in an status information database

• Payment failed
• E.g., track dedicated event with a new service


that notifies customer and/or online shop

• Cashing coupon failed
• E.g., send out dedicated event that a new service

subscribes to

• New service then places task in desk officer’s inbox
• Integrate new video library (different API)
• Implement new service
• Replace existing service with new service

Feels a lot like recurring patterns …

What did we learn so far?

Comparing the paradigms …

• Decomposition
• Vertically divide-and-conquer vs. horizontally go-with-the-flow
• Coordination
• Coordination logic/services and orchestration vs. event chains and choreography
• Transactions
• Built-in transaction handling vs. external supervision
• Error handling
• Built into service vs. escalation/supervision strategy
• Separation of concerns
• Multiple responsibilities service vs. single responsibility services
• Encapsulation
• Domain logic distributed across services vs. domain logic in one place
• Complexity
• A draw …

Different communication paradigms lead to very different service designs

… which means different options to address a given problem

Related areas and limitations

Mixing communication paradigms

Mixing paradigms

• Always an option
• Note the trade-off between design purity

and solution mismatch complexity

• A (very) simple heuristic
• Single functionality
• All-or-nothing characteristic
• Single domain

Ø Synchronous request/response

• Multiple functionalities
• Flow/Process characteristic
• Multiple domains

Ø Asynchronous messaging

What if the paradigm is fixed?

Fixed paradigm

• You can simulate other paradigms
• E.g., simulate sync. r/r with async. messaging
• E.g., simulate async. commands with sync. r/r
• Will support the service design topic
• Apart from that it is a (lame) compromise

What about user interaction?

User interaction

• Interaction with user client is usually r/r
• Use web sockets if available
• Use the mediator pattern with timeouts
• Could be implemented via a BFF service
• Complement with processing status page

Can we apply the same patterns inside process boundaries?

Inside process boundaries

• Have the process context in mind
• Without threads
• If your downstream call dies, you are also dead
• Usually synchronous r/r is appropriate
• Otherwise single-threaded scheduler is needed
• With threads
• “Multi-process light”
• Better multi-threading resilience possible
• More design options

Wrap-up

• The one-size-fits-all trap
• Communication paradigms
• The synchronous-r/r-everywhere trap
• Designing communication
• Influence on service design

Different communication paradigms
 lead to very different service designs

There is no “one-size-fits-all” solution

@ufried

Uwe Friedrichsen | uwe.friedrichsen@codecentric.de | http://slideshare.net/ufried | http://ufried.tumblr.com