'Dark Launching' refers to feature enablement in production behind the scenes, like 'Shadow Testing', which is the testing process of new application features in the background without making them generally available. It aims to activate new software features before the GA without interrupting the operations and being transparent to customers. During the testing phase, you are to monitor, for example, whether the new integration works seamlessly with existing components under realistic data and load. In services landscape, for instance, 'Shadow Testing' enables development teams to execute endpoint switches of service dependencies in a graceful way by calling both endpoints, say, A and B, and comparing their API responses.
Shade is a small library for Java, which allows you to test new application features in the background. You can simply add the following maven dependency to your project:
<dependency>
<groupId>net.reevik</groupId>
<artifactId>shade</artifactId>
<version>0.3.0</version>
</dependency>You can consider the following code snippet, it is how the routing configuration and router instance are instantiated:
RoutingConfiguration<String> routingConfiguration=Builder.<String>create()
.withSideA(()-> serviceOld.call())
.withSideB(()-> serviceNew.call())
.withResultValidator(mustEqual())
.withRoutingCriterion(countingCriterion)
.withRoutingMode(RoutingMode.A_SIDE)
.build();
EndpointRouter<String> router=new EndpointRouter<>(routingConfiguration);
String result=router.route();The RoutingConfiguration takes two commands which implement the integration logic with the A and B components. The RoutingConfiguration instance requires a validator which is used to validate the resulting objects from A and B calls, whereas a routing criterion to decide when the B side needs to be called. You can configure the router, e.g., for every tenth requests to hit the B side. The Routing Mode defines the operating mode of the EndpointRouter. A_SIDE is used to route all requests to the A endpoint (the existing integration), which effectively enables A component, and B_SIDE works like A_SIDE, but this time all requests will be routed to the B component (the new integration). SHADOW_MODE_PASSIVE results in calling both endpoints simultaneously. If the A-B validation succeeds, in other words A and B component calls' results are compatible, the EndpointRouter returns the result object from the A side, SHADOW_MODE_ACTIVE, in case the A-B validation succeeds, it returns the result object from the B side.
The modes which require both sides to get activates, like SHADOW_MODE_PASSIVE, leverage Java's virtual threads. So, it is important to note that using synchronized blocks within the command implementation may end up with pinned platform threads. Therefore, I encourage you to use, ReentrantLocks instead.
Result validation is used to evaluate the result objects from both integration so that the framework can take action if two results are compatible or incompatible. Depending on the routing mode selected, if both results are equal, the routed may return the result object from the new integration. It means, the Shade can roll out the new feature by activating the new integration if the validation passes.
Shade brings a few simple validators, which you can use out-of-the-box. Let's take two of them, which, I presume, will be used mostly:
Anyway, the validators are not limited to those above. You can write your own validators depending on your needs by extending the framework.
Routing criteria are preconditions for the router to determine when to enable the new integration. For example, the CountingCondition implements the logic which allows every n'th request to be routed to the new integration. Like validators, the framework brings a few criteria implementation out-of-the-box.
For bugs, questions and discussions please use the GitHub Issues.
Copyright 2023 Erhan Bagdemir
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