watch your communication - goto conference...the flipside of the coin • http was designed for a...

Watch your communication How communication drives design

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

@ufried Uwe Friedrichsen | [email protected] | 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, only using a hammer might be adequate

If your task is also to paint the box you just built, only having a hammer might be a problem …

Now imagine building a whole housejust 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 •  Total price

•  Credit card payment

•  Only non-digital items

Order Fulfillment Service

Online Shop

Payment Service

Credit Card Provider

Shipment Service

Warehouse System

<Foreign Service> <Own Service>

Credit Card

Coordinate

Warehouse

Order fulfillment Add coupons •  Order additionally includes

•  Optional coupon ID •  Optional remaining coupon value •  Coupon is already charged against total price

•  Validate coupon


Online Shop

Payment Service

Shipment Service

Warehouse System


Coupon Management

Coupon Credit Card

Coordinate

Warehouse

Coordinate


Order fulfillment Add promotions •  Order additionally includes

•  Optional promotion ID •  Promotion is already applied to order

•  Notify Campaign Management System about promotion usage


Online Shop

Payment Service

Shipment Service

Warehouse System


Coupon Management

Coupon Campaign

Management Promotion

Credit Card

Coordinate

Warehouse

Coordinate


Order fulfillment Add customer accounts •  Order additionally includes

•  Payment type (Credit card/Account)

•  Charge customer account


Online Shop

Payment Service

Shipment Service

Warehouse System


Coupon Management

Campaign Management

Account service

Accounts Receivables

Coordinate

Warehouse


Coupon

Promotion

Credit Card

Coordinate

Order fulfillment Add PayPal •  Order additionally includes

•  More payment types (Credit card/PayPal/Account)

•  Payment via PayPal


Online Shop

Payment Service


Shipment Service

Warehouse System


Coupon Management

Promotion Campaign

Management

Account service

Payment provider

PayPal


Coupon

Credit Card

Coordinate

Warehouse

PayPal

Coordinate

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


Online Shop

Payment Service


Shipment Service

Warehouse System


Coupon Management

Promotion Campaign

Management

Account service

Payment provider

PayPal


Music Library

E-Mail Server

Coupon

Credit Card

Coordinate

Warehouse

Coordinate

Music

Notify Cust.

PayPal

Coordinate

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


Online Shop

Payment Service


Shipment Service

Warehouse System


Coupon Management

Promotion Campaign

Management

Account service

Payment provider

PayPal


Music Library Video Library

E-Mail Server

Coupon

Credit Card

Coordinate

Warehouse

Coordinate

Assets

Notify Cust.

PayPal

Coordinate

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


Online Shop

Payment Service


Shipment Service

Warehouse System


Coupon Management

Promotion Campaign

Management

Account service

Payment provider

PayPal


Music Library

E-Book Library

Video Library

E-Mail Server

Coupon

Credit Card

Coordinate

Warehouse

Coordinate

Assets

Notify Cust.

PayPal

Coordinate

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


Online Shop

Payment Service


Shipment Service

Warehouse System


Coupon Management

Promotion Campaign

Management Loyalty

Account service

Payment provider

PayPal

Loyalty Management


Music Library

E-Book Library

Video Library

E-Mail Server

Coupon

Credit Card

Coordinate

Warehouse

Coordinate

Assets

Notify Cust.

PayPal

Coordinate

Order fulfillment

More requirements to come …


Online Shop

Payment Service


Shipment Service

Warehouse System


Coupon Management

Promotion Campaign

Management Loyalty

Account service

Payment provider

PayPal

Loyalty Management


Music Library

E-Book Library

Video Library

E-Mail Server

Coupon

Credit Card

Coordinate

Warehouse

Coordinate

Assets

Notify Cust.

PayPal

Coordinate

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 •  Total price

•  Credit card payment

•  Only non-digital items

Order confirmed

Online Shop


Warehouse System

<Foreign Service>

<Own Service>

Credit Card Service

Warehouse Service

Payment authorized

<Event>

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


Warehouse System

<Foreign Service>

<Own Service>

Credit Card Service

Warehouse Service

Payment authorized

<Event>

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


Warehouse System

<Foreign Service>

<Own Service>

Coupon Management

Campaign Management

Credit Card Service

Warehouse Service

Promotion Service

Coupon Service

Payment authorized

<Event>

Payment failed

Order fulfillment Add customer accounts •  Order additionally includes

•  Payment type (Credit card/Account)

•  Charge customer account

Order confirmed

Online Shop


Warehouse System

<Foreign Service>

<Own Service>

Coupon Management

Campaign Management

Account service

Credit Card Service


Warehouse Service

Promotion Service

Coupon Service

Payment authorized

Payment failed

<Event>

Order fulfillment Add PayPal •  Order additionally includes

•  More payment types (Credit card/PayPal/Account)

•  Payment via PayPal

Order confirmed

Online Shop


Warehouse System

<Foreign Service>

<Own Service>

Coupon Management

Campaign Management

Account service

Credit Card Service


PayPal

PayPal Service

Warehouse Service

Promotion Service

Coupon Service

Payment authorized

Payment failed

<Event>

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


Warehouse System

<Foreign Service>

<Own Service>

Coupon Management

Campaign Management

Account service

Credit Card Service


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

<Event>

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


Warehouse System

<Foreign Service>

<Own Service>

Coupon Management

Campaign Management

Account service

Credit Card Service


Music Library

Video Library E-Mail Server

PayPal

PayPal Service

Warehouse Service

Promotion Service

Coupon Service


Video Library Service



Payment failed

<Event>

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


Warehouse System

<Foreign Service>

<Own Service>

Coupon Management

Campaign Management

Account service

Credit Card Service


Music Library

E-Book Library


PayPal

PayPal Service

Warehouse Service

Promotion Service

Coupon Service



E-Book Library Service



Payment failed

<Event>

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


Warehouse System

<Foreign Service>

<Own Service>

Coupon Management

Campaign Management

Account service

Credit Card Service

Loyalty Management


Music Library

E-Book Library


PayPal

PayPal Service

Warehouse Service

Promotion Service

Bonus Card Service

Coupon Service






Payment failed

<Event>

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

Order confirmed

Online Shop


Warehouse System

<Foreign Service>

<Own Service>

Coupon Management

Campaign Management

Account service

Credit Card Service

Loyalty Management


Music Library

E-Book Library


PayPal

PayPal Service

Warehouse Service

Promotion Service

Bonus Card Service

Coupon Service





Order fulfillment supervisor


Payment failed

<Event>

Track flow of events. Reschedule events in case of failure

Services are responsible to eventually succeed or fail for good, usually incorporating a supervision/escalation hierarchy for that

Order confirmed

Online Shop


Warehouse System

<Foreign Service>

<Own Service>

Coupon Management

Campaign Management

Account service

Credit Card Service

Loyalty Management


Music Library

E-Book Library


PayPal

PayPal Service

Warehouse Service

Promotion Service

Bonus Card Service

Coupon Service






Payment failed

<Event>

Order fulfillment supervisor

Track flow of events Reschedule events in case of failure

Services are responsible to eventually succeed or fail for good, usually incorporating a supervision/escalation hierarchy for that 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 thatwould 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

officer ’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 storethem 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 | [email protected] | http://slideshare.net/ufried | http://ufried.tumblr.com