Abstract Retrofit from your API

RetroDoggo.kt

interface RetroDogApi {
  @GET("/dogs/{doggoName}")
  Flowable<Dog> getDoggo(@Path("doggoName") String doggoName);
}

interface DogApi {
  Flowable<Dog> getDoggo(String doggoName);
}

class DogClient(val urlA: String, val urlB: String): DogApi {
  private val retroDogApiA: RetroDogApi
  private val retroDogApiB: RetroDogApi
  init {
    val retrofitA = Retrofit.Builder()
      .baseUrl(urlA)
      .build()
    retroDogApiA = retrofit.create(RetroDogApi::class.java)
    
    val retrofitB = Retrofit.Builder()
      .baseUrl(urlB)
      .build()
    retroDogApiB = retrofit.create(RetroDogApi::class.java)
  }
  
  Flowable<Dog> getDoggo(String doggoName) {
    if (shouldUseApiA()) {
      return retroDogApiA.getDoggo(doggoName)
    } else {
      return retroDogApiB.getDoggo(doggoName);
    }
  }
  
  fun shouldUseApiA(): boolean {
    // logic here
  }
}

class UseIt {
  fun use() {
    val dogApi = DogClient("https://doggo.dogs/servicea", "https://doggo.dogs/serviceb")
    dogApi.getDoggo("fido")
      .subscribeOn(...)
      .observeOn(...)
      .subscribe(...)
  }
}