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docs: update strangler

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Ilkka Seppälä
2024-05-27 13:04:33 +03:00
parent 10f37987d2
commit aed840d72c
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strangler/README.md
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@@ -113,18 +113,61 @@ public class NewArithmetic {
The `NewArithmetic` class represents the system after the migration process. It only depends on the `NewSource` class. All methods now use the new source.
Here is the `main` method executing our example.
```java
public static void main(final String[] args) {
final var nums = new int[]{1, 2, 3, 4, 5};
//Before migration
final var oldSystem = new OldArithmetic(new OldSource());
oldSystem.sum(nums);
oldSystem.mul(nums);
//In process of migration
final var halfSystem = new HalfArithmetic(new HalfSource(), new OldSource());
halfSystem.sum(nums);
halfSystem.mul(nums);
halfSystem.ifHasZero(nums);
//After migration
final var newSystem = new NewArithmetic(new NewSource());
newSystem.sum(nums);
newSystem.mul(nums);
newSystem.ifHasZero(nums);
}
```
Console output:
```
13:02:25.030 [main] INFO com.iluwatar.strangler.OldArithmetic -- Arithmetic sum 1.0
13:02:25.032 [main] INFO com.iluwatar.strangler.OldSource -- Source module 1.0
13:02:25.032 [main] INFO com.iluwatar.strangler.OldArithmetic -- Arithmetic mul 1.0
13:02:25.032 [main] INFO com.iluwatar.strangler.OldSource -- Source module 1.0
13:02:25.032 [main] INFO com.iluwatar.strangler.HalfArithmetic -- Arithmetic sum 1.5
13:02:25.032 [main] INFO com.iluwatar.strangler.HalfSource -- Source module 1.5
13:02:25.033 [main] INFO com.iluwatar.strangler.HalfArithmetic -- Arithmetic mul 1.5
13:02:25.033 [main] INFO com.iluwatar.strangler.OldSource -- Source module 1.0
13:02:25.033 [main] INFO com.iluwatar.strangler.HalfArithmetic -- Arithmetic check zero 1.5
13:02:25.033 [main] INFO com.iluwatar.strangler.HalfSource -- Source module 1.5
13:02:25.034 [main] INFO com.iluwatar.strangler.NewArithmetic -- Arithmetic sum 2.0
13:02:25.034 [main] INFO com.iluwatar.strangler.NewSource -- Source module 2.0
13:02:25.034 [main] INFO com.iluwatar.strangler.NewArithmetic -- Arithmetic mul 2.0
13:02:25.034 [main] INFO com.iluwatar.strangler.NewSource -- Source module 2.0
13:02:25.034 [main] INFO com.iluwatar.strangler.NewArithmetic -- Arithmetic check zero 2.0
13:02:25.035 [main] INFO com.iluwatar.strangler.NewSource -- Source module 2.0
```
This is a typical example of the Strangler pattern. The legacy system (`OldArithmetic`) is gradually replaced by the new system (`HalfArithmetic` and `NewArithmetic`). The new system is developed incrementally, and at each stage, it strangles a part of the legacy system until the legacy system is completely replaced.
## Class diagram
![Strangler](./etc/strangler.png "Strangler")
## Applicability
* Use when you need to replace a monolithic or legacy system incrementally.
* Ideal for scenarios where the system cannot be replaced in one go due to risk or complexity.
* Suitable when you need to modernize parts of an application while ensuring continuous operation.
## Tutorials
* [Legacy Application Strangulation: Case Studies (Paul Hammant)](https://paulhammant.com/2013/07/14/legacy-application-strangulation-case-studies/)
## Known Uses
* Replacing a legacy monolithic application with a microservices architecture.
@@ -156,5 +199,4 @@ Trade-offs:
* [Building Microservices](https://amzn.to/3UACtrU)
* [Patterns of Enterprise Application Architecture](https://amzn.to/3WfKBPR)
* [Refactoring: Improving the Design of Existing Code](https://amzn.to/3TVEgaB)
* [Strangler pattern - Microsoft](https://docs.microsoft.com/en-us/azure/architecture/patterns/strangler)
* [Legacy Application Strangulation: Case Studies - Paul Hammant](https://paulhammant.com/2013/07/14/legacy-application-strangulation-case-studies/)
* [Strangler pattern (Microsoft)](https://docs.microsoft.com/en-us/azure/architecture/patterns/strangler)