private ConfigResponse createConfigResponse(ConfigKey<?> configKey, GetConfigRequest req, ConfigResponseFactory responseFactory) {
        ConfigDefinition def = getTargetDef(req);
        if (def == null) {
            metricUpdater.incrementFailedRequests();
            throw new UnknownConfigDefinitionException("Unable to find config definition for '" + configKey.getNamespace() + "." + configKey.getName());
        }
        log.log(Level.FINE, () -> TenantRepository.logPre(getId()) + "Resolving " + configKey + " with config definition " + def);

        var payload = createPayload(configKey, def);

        return responseFactory.createResponse(payload.getFirst(), applicationGeneration, payload.getSecond(), req.configPayloadChecksums());
    }
Gets a config from ZK. Returns null if not found.
configserver/src/main/java/com/yahoo/vespa/config/server/application/Application.java