For servable models saved from Paddle Serving IO API, users do not need to do extra coding work to startup a service, but may need some coding work on the client side. For development of Web Service plugin, a user needs to provide implementation of Web Service's preprocessing and postprocessing work if needed to get a HTTP service. ### 2.2 Industrial Features Paddle Serving takes into account a series of issues such as different operating systems, different development languages, multiple hardware devices, cross-deep learning platform model conversion, distributed sparse parameter indexing, and cloud deployment by different teams in industrial-level scenarios. > Cross-platform operation Cross-platform is not dependent on the operating system, nor on the hardware environment. Applications developed under one operating system can still run under another operating system. Therefore, the design should consider not only the development language and the cross-platform components, but also the interpretation differences of the compilers on different systems. Docker is an open source application container engine that allows developers to package their applications and dependencies into a portable container, and then publish it to any popular Linux machine or Windows machine. We have packaged a variety of Docker images for the Paddle Serving framework. Refer to the image list《[Docker Images](Docker_Images_EN.md)》, Select mirrors according to user's usage. We provide Docker usage documentation《[How to run PaddleServing in Docker](Install_EN.md)》.Currently, the Python webservice mode can be deployed and run on the native Linux and Windows dual systems.《[Paddle Serving for Windows Users](Windows_Tutorial_EN.md)》 > Support multiple development languages client SDKs Paddle Serving provides 3 development language client SDKs, including Python, C++, Java, we hope that interested open source developers can help submit PR. + Python, Refer to the client example under python/examples or 4.2 web service example. + C++, Refer to《[从零开始写一个预测服务](C++_Serving/Creat_C++Serving_CN.md)》 + Java, Refer to《[Paddle Serving Client Java SDK](Java_SDK_EN.md)》 > Support multiple hardware devices The inference framework of the well-known deep learning platform only supports CPU and GPU inference on the X86 platform. With the rapid increase in the complexity of AI algorithms, the computing power of chips has greatly increased, which has promoted the accelerated implementation of IoT applications and deployment on a variety of hardware.Paddle Serving integrates high-performance inference engine Paddle Inference and mobile terminal inference engine Paddle Lite, Provide inference services on multiple hardware devices. At present, in addition to X86 CPU and GPU, Paddle Serving has implemented the deployment of inference services on ARM CPU and Kunlun XPU. In the future, more hardware will be added to Paddle Serving. > Model conversion across deep learning platforms Models trained on other deep learning platforms can be passed《[PaddlePaddle/X2Paddle工具](https://github.com/PaddlePaddle/X2Paddle)》.We convert multiple mainstream CV models to Paddle models. TensorFlow, Caffe, ONNX, PyTorch model conversion is tested.《[AIStudio教程-Paddle Serving服务化部署框架](https://www.paddlepaddle.org.cn/tutorials/projectdetail/1555945)》 Because it is impossible to directly view the feed and fetch parameter information in the model file, it is not convenient for users to assemble the parameters. Therefore, Paddle Serving developed a tool to convert the Paddle model into Serving format and generate a prototxt file containing feed and fetch parameter information. The following figure is the generated prototxt file of the uci_housing example. For more conversion methods, refer to the document《[How to save a servable model of Paddle Serving?](Save_EN.md)》. ``` feed_var { name: "x" alias_name: "x" is_lod_tensor: false feed_type: 1 shape: 13 } fetch_var { name: "fc_0.tmp_1" alias_name: "price" is_lod_tensor: false fetch_type: 1 shape: 1 } ``` > Distributed Sparse Parameter Indexing Distributed Sparse Parameter Indexing is commonly seen in advertising and recommendation scenarios, and is often used coupled with distributed training. The figure below explains a commonly seen architecture for online recommendation. When the recommendation service receives a request from a user, the system will automatically collects training log for the offline distributed online training. Mean while, the request is sent to Paddle Serving Server. For sparse features, distributed sparse parameter index service is called so that sparse parameters can be looked up. The dense input features together with the looked up sparse model parameters are fed into the Paddle Inference Node of the DAG in Paddle Serving Server. Then the score can be responsed through RPC to product service for item ranking.
Why do we need to support distributed sparse parameter indexing in Paddle Serving? 1) In some recommendation scenarios, the number of features can be up to hundreds of billions that a single node can not hold the parameters within random access memory. 2) Paddle Serving supports distributed sparse parameter indexing that can couple with paddle inference. Users do not need to do extra work to have a low latency inference engine with hundreds of billions of parameters. ---- ## 3. C++ Serving design C++ Serving aims to achieve high-performance reasoning services with high concurrency and low latency. Its network framework and core execution engine are written based on C/C++, and provide powerful industrial-grade application capabilities, including model management, model security, and A/B Testing ### 3.1 Network Communication Mechanism Paddle Serving adopts [brpc](https://github.com/apache/incubator-brpc) as underlying communication layer. brpc is an open-source RPC communication library with high concurrency and low latency advantages compared with other open source RPC library. Millions of instances and thousands of services are using brpc within Baidu. ### 3.2 Core Execution Engine The core execution engine of Paddle Serving is a Directed acyclic graph(DAG). In the DAG, each node represents a phase of inference service, such as paddle inference prediction, data preprocessing and data postprocessing. DAG can fully parallelize the computation efficiency and can fully utilize the computation resources. For example, when a user has input data that needs to be feed into two models, and combine the scores of the two models, the computation of model scoring is parallelized through DAG.
### 3.3 Model Management and Hot Reloading C++ Serving supports model management functions, including management of multiple models and multiple model versions.In order to ensure the availability of services, the model needs to be hot loaded without service interruption. Paddle Serving supports this feature and provides a tool for monitoring output models to update local models. Please refer to [Hot loading in Paddle Serving](C++_Serving/Hot_Loading_EN.md) for specific examples. ### 3.4 MOEDL ENCRYPTION INFERENCE Paddle Serving uses a symmetric encryption algorithm to encrypt the model, and decrypts it in memory during the service loading model. At present, providing basic model security capabilities does not guarantee absolute model security. Users can improve them according to our design to achieve a higher level of security. Documentation reference《[MOEDL ENCRYPTION INFERENCE](C++_Serving/Encryption_EN.md)》 ### 3.5 A/B Test After sufficient offline evaluation of the model, online A/B test is usually needed to decide whether to enable the service on a large scale. The following figure shows the basic structure of A/B test with Paddle Serving. After the client is configured with the corresponding configuration, the traffic will be automatically distributed to different servers to achieve A/B test. Please refer to [ABTEST in Paddle Serving](C++_Serving/ABTest_EN.md) for specific examples.
### 3.6 Micro service plugin The underlying communication of Paddle Serving is implemented with C++ as well as the core framework, it is hard for users who do not familiar with C++ to implement new Paddle Serving Server Operators. Another approach is to use the light-weighted Web Service in Paddle Serving Server that can be viewed as a plugin. A user can implement complex data preprocessing and postprocessing logics to build a complex AI service. If access of the AI service has a large volumn, it is worth to implement the service with high performance Paddle Serving Server operators. The relationship between Web Service and RPC Service can be referenced in `User Type`. ---- ## 4. Python Webservice Design ### 4.1 Network Communication Mechanism There are many open source frameworks for web services. Paddle Serving currently integrates the Flask framework, but this part is not visible to users. In the future, a better-performing web framework may be provided as the underlying HTTP service integration engine. ### 4.2 Web Service Development `WebService` is a Base Class, providing inheritable interfaces such `preprocess` and `postprocess` for users to implement. In the inherited class of `WebService` class, users can define any functions they want and the startup function interface is the same as RPC service. ``` python from paddle_serving_server.web_service import WebService from imdb_reader import IMDBDataset import sys class IMDBService(WebService): def prepare_dict(self, args={}): if len(args) == 0: exit(-1) self.dataset = IMDBDataset() self.dataset.load_resource(args["dict_file_path"]) def preprocess(self, feed={}, fetch=[]): if "words" not in feed: exit(-1) res_feed = {} res_feed["words"] = self.dataset.get_words_only(feed["words"])[0] return res_feed, fetch imdb_service = IMDBService(name="imdb") imdb_service.load_model_config(sys.argv[1]) imdb_service.prepare_server( workdir=sys.argv[2], port=int(sys.argv[3]), device="cpu") imdb_service.prepare_dict({"dict_file_path": sys.argv[4]}) imdb_service.run_server() ``` ---- ## 5. Python Pipeline Serving Design The end-to-end deep learning model is currently unable to solve all problems. The use of multiple deep learning models together is still a conventional means to solve real-world problems. the end-to-end deep learning model can not solve all the problems at present. Usually, it is necessary to use multiple deep learning models to solve practical problems. ### 5.1 Network Communication Mechanism The network framework of Pipeline Serving uses gRPC and gPRC gateway. The gRPC service receives the RPC request, and the gPRC gateway receives the RESTful API request and forwards the request to the gRPC Service through the reverse proxy server. Therefore, the network layer of Pipeline Serving receives both RPC and RESTful API.
