Java canary tools

Contrary to popular beliefs, I don't think canaries requires infrastructure components set up. Routing a subset of users can be done using hashing or sampling.

(Reference: Twitter)

Marco then responded with saying that "go live and deployment" don't need to be the same thing.

This library contains a few useful Java tools to be able to run soft experiments in a Java application without having to do a redeploy. As long as you have a sane object-oriented application adhering to the Interface segregation principle, using these tools should be easy.

This Java package contains utility classes to run experiments and safe rollouts of new implementations of Java interfaces:

• WeightedRoundRobinBuilder allows you delegate a random fraction of calls to another implementation(s) of a shared Java interface. Usually useful if you have a different implementation that you would like to behave in the exact same way (including, having the same side-effect).
• WeightedShardedBuilder constructs a Java proxy that implements a Java interface shared between different implementations. The proxy delegates to downstream implementations using Object#hashCode() of the first method argument, weighted by the downstream implementation (can be customized). This class is useful if you would like to try out a new Java implementation for a subset of, for example, users. This is useful if you are switching from one implementation to another which will not necessarily behave in the same way (nor have the same side-effects).
• CircuitBreakerFallbackBuilder allows you to do safe rollout of new Java interface implementations. Use CircuitBreakerFallbackBuilder to construct a Java Proxy class that wraps two implementations of the same Java interfaces, the old implementation and the new implementation. As long as the new implementation never throws any exception, the Proxy class will start using it more and more instead of old. If new starts throwing exceptions, the Proxy class will quickly roll back to use the old implementation. Thus, significantly reducing Mean Time To Recovery (MTTR).

Examples

WeightedRoundRobinBuilder

MyInterface proxy =
    new WeightedRoundRobinBuilder<TestInterface>()
        .add(1, newImplementation)
        .add(100, oldImplementation)
        .build(MyInterface.class);

WeightedShardedBuilder

MyInterface proxy =
    new WeightedShardedBuilder<TestInterface>()
        .add(1, newImplementation)
        .add(100, oldImplementation)
        .build(MyInterface.class, EXPERIMENT_SEED);

This will use the Object#hashCode of the first parameter on each method call to figure out which implementation to delegate to. Call WeightedShardedBuilder#setParamSelector to customize how you will figure out which implementation to be consequently called.

CircuitBreakerFallbackBuilder

MyInterface proxy =
    new CircuitBreakerFallbackBuilder()
        .build(
            MyInterface.class,
            oldImplementation,
            newImplementation);

Experiment with parameters

You can use the simulation Gradle application to play around with the CircuitBreakerFallbackBuilder parameters. This is what a simulation looks like:

$ gradle run :simulation:run

> Task :simulation:run
ms oldImplCalls newImplCalls oldImplExceptions newImplExceptions nPhase1Samples nPhase2Samples
0 0 61 0 0 61 0
60000 0 60 0 0 60 0
120000 2 58 0 0 60 0
180000 0 60 0 0 60 0
240000 0 60 0 0 60 0
300000 0 60 0 0 60 0
360000 1 59 0 0 60 0
420000 0 60 0 0 60 0
480000 9 51 0 32 19 41
540000 20 40 0 40 0 60
600000 38 22 0 22 0 60
660000 60 0 0 0 0 60
720000 60 0 0 0 0 60
780000 59 1 0 1 0 60
840000 60 0 0 0 0 60
900000 59 1 0 1 0 60
960000 39 0 0 0 0 39

BUILD SUCCESSFUL in 1s
13 actionable tasks: 1 executed, 12 up-to-date

Notice how as soon as the new implementation starts throwing exceptions, calls will instead be delegated to the old implementation.

The following will list the parameters you can play around with:

$ gradle run :simulation:run --args="--help"

> Task :simulation:run
Flags:

--phase-shift
--steps
--seed
--failure-penalty
--success-credits
--epsilon
--slots
--slot-duration
--duration-per-step
--phase1-orig-impl-error-ratio
--phase1-new-impl-error-ratio
--phase2-orig-impl-error-ratio
--phase2-new-impl-error-ratio

BUILD SUCCESSFUL in 1s
13 actionable tasks: 1 executed, 12 up-to-date