@Get("/api/v2/services")
  @Blocking
  public AggregatedHttpResponse getServiceNames(ServiceRequestContext ctx) throws IOException {
    List<String> serviceNames = storage.serviceAndSpanNames().getServiceNames().execute();
    serviceCount = serviceNames.size();
    return maybeCacheNames(serviceCount > 3, serviceNames, ctx.alloc());
  }
The Cache-Control max-age (seconds) for /api/v2/services /api/v2/remoteServices and
/api/v2/spans
zipkin-server/src/main/java/zipkin2/server/internal/ZipkinQueryApiV2.java