How to Split Your System into Microservices

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How to Split Your System into Microservices Eberhard Wolff @ewolff Fellow

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http://continuous-delivery-buch.de/

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http://microservices-buch.de/ http://microservices-book.com/

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http://microservices-book.com/primer.html FREE!!!!

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Microservices: Definition > No consistent definition > Microservices are modules > Independent deployment units > E.g. Docker container > Microservice owned by one team

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Microservices: Definition Server / Container Server / Container Micro Service Micro Service

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Microservices aim for decoupling

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Why is the Split so Important? > Microservices implement a part of the logic > Allow isolated development of features > …and independent teams > If split is wrong, you won’t achieve goals. > …and there is just more complexity. > But there are even more goals!

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Why Microservices? Strong Modularization Scaling Agile Sustainable development Replaceable Services Continuous Delivery Free choice of technology Handle Legacy efficient Independent Scaling Robustness Small teams develop and deploy independently Add services – not code Small Services Failure limited to single Microservice

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Why Microservices? Scaling Agile Sustainable development Continuous Delivery Free choice of technology Handle Legacy efficient Independent Scaling Robustness Organization Deployment Units Technology

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There are many reasons for microservices.

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There are many scenarios for microservices.

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Scenario and reason influence the split.

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Bounded Context

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UBIQUITOUS LANGUAGE VALUE OBJECT ENTITY

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Address VALUE OBJECT ENTITY or

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529 pages

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529 pages Part IV

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529 pages Part IV Chapter 14

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A domain model is only useful in a BOUNDED CONTEXT.

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There is no universal data model in a large system.

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Address for a customer VALUE OBJECT ENTITY or

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Address for calculating the drones’ routes VALUE OBJECT ENTITY or

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Microservice = Bounded Context

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Create some Bounded Contexts! Sir, yes, sir!

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Why would you build a universal data model if that is neither possible nor useful??

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Bounded Context: Challenge > Not a way to design a great architecture > …but consequence of good domain architecture > i.e. clearly separated domains will lead to separated BOUNDED CONTEXTS > …containing logic and data > How can you find BOUNDED CONTEXTS?

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Bounded Context: Challenge > Coarse-grained > Ideal: implement a functionality in one unit > Ideal: Independence > Might have relationships > …limiting independence

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Divide by Use Cases > Microservice should implement a use case > …ideally without calling other microservices > Divide use cases among microservices > …then decide about the BOUNDED CONTEXT

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Browsing Registration Creating Microservices User Registration Search Products by Keywords Browse Products by Category Checkout Payment Define Shipment Update Profile Basic customer data Preferences Recommendations Billing address Payment information All these services have data about the customer!!

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Bounded Context Scaling Agile Sustainable development Continuous Delivery Free choice of technology Handle Legacy efficient Independent Scaling Robustness Organization Deployment Units Technology

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What about other scenarios??

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Existing Architecture Product Customer Warehouse Product Service Customer Service Warehouse Service iOS Android PoS Web

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Let’s create some Bounded Contexts!

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Existing Architecture Product Customer Warehouse Product Service Customer Service Warehouse Service iOS Android PoS Web Browsing

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Bounded Contexts > Browsing distributed in many artifacts > Change to Browsing might influence all of them > …or not > BOUNDED CONTEXTS would be desirable

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Migrate to Bounded Context Product Customer Warehouse Product Service Customer Service Warehouse Service iOS Android PoS Web Browsing Browsing

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Introducing Bounded Contexts > …would change the architecture completely > …might be very hard > …and risky > Is it worth it? > Is it even doable? > Might also change the organization

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Add services Product Customer Warehouse Product Service Customer Service Warehouse Service iOS Android PoS Web

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Add services Product Customer Warehouse Product Service Customer Service Warehouse Service iOS Android PoS Web News- letter Web

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Add Service > Might replace the old system stepwise > Immediate benefits > Low risk > Major reason for microservices

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Cut existing services Product Customer Warehouse Product Service Customer Service Warehouse Service iOS Android PoS Web

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Existing Architecture Scaling Agile Sustainable development Continuous Delivery Free choice of technology Handle Legacy efficient Independent Scaling Robustness Organization Deployment Units Technology

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Existing Architecture > ...has an impact on the target architecture > What good is an architecture you cannot migrate into? > Might overrule everything else > Even BOUNDED CONTEXT

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Browsing Registration External Systems User Registration Search Products by Keywords Browse Products by Category Checkout Payment Define Shipment Update Profile Browse Products by Category Payment Provider Logistic Partner

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Browsing Registration External Systems User Registration Search Products by Keywords Browse Products by Category Checkout Update Profile Browse Products by Category Payment Provider Logistic Partner Payment Shipping

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External Systems > Limit integration for each external system to one Microservice > External system might belong to a domain > …or BOUNDED CONTEXT > ...or not > Simplifies integration > Easier to achieve robustness

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External Systems Scaling Agile Sustainable development Continuous Delivery Free choice of technology Handle Legacy efficient Independent Scaling Robustness Organization Deployment Units Technology

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We expect a lot more registrations!

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Browsing Registration External Systems User Registration Search Products by Keywords Browse Products by Category Checkout Payment Define Shipment Update Profile Browse Products by Category

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Browsing Registration External Systems Search Products by Keywords Browse Products by Category Checkout Payment Define Shipment Browse Products by Category Regis- tration Update Profile

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Technical Reasons > Independent scalability is just one technical reason > There are many more > Might be OK to share database in this scenario > Might even split read and write

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CQRS > Command – Query Responsibility Segregation > Commands change data > Query provide data > Implement in separate microservices

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Command Queue Command Command Command Command Handler Query Handler Command Store Database Read Replica

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Technical Reasons Scaling Agile Sustainable development Continuous Delivery Free choice of technology Handle Legacy efficient Independent Scaling Robustness Organization Deployment Units Technology

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Registration Requirements Browsing Checkout Marketing Sales Fulfillment Finance

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Requirements > One microservice should implement one stream of requirements > Otherwise: coordinate priorities > …and therefore less independence

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Registration Requirements Browsing Payment Marketing Sales Fulfillment Finance Shipping

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Requirements Scaling Agile Sustainable development Continuous Delivery Free choice of technology Handle Legacy efficient Independent Scaling Robustness Organization Deployment Units Technology

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Conclusion

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Microservices = Bounded Context

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Split Bounded Context Migration External Systems Technical Reasons Require- ments

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