public Optional<Duration> hostTTL(Environment environment, Optional<RegionName> region) {
        return zones().stream()
                      .filter(zone -> zone.concerns(environment, region))
                      .findFirst()
                      .flatMap(DeploymentSpec.DeclaredZone::hostTTL)
                      .or(() -> hostTTL);
    }
Returns the host TTL to use for given environment and region, if any
config-model-api/src/main/java/com/yahoo/config/application/api/DeploymentInstanceSpec.java