[Alibaba middleware technology series] "Nacos technology" service registration and discovery related principle analysis

Background introduction

The previous articles introduced Nacos Configure the capability mechanism of the central service , Next , Let's introduce Nacos Another very important feature is service registration and discovery , When it comes to service registration and discovery, I believe everyone should be familiar with it , In today's Micro service era , Service is very important , And in the Nacos Chinese service is called his first-class citizen .Nacos Support almost all major types of “ service ” Discovery 、 Configure and manage .

service (Service)

Service refers to one or a group of software functions （ For example, retrieval of specific information or execution of a group of operations ）, Its purpose is that different clients can be reused for different purposes （ For example, through cross process network call ）.Nacos Support mainstream service Ecology , Such as Kubernetes Service、gRPC|Dubbo RPC Service perhaps Spring Cloud RESTful Service.

nacos As shown in the architecture diagram of

(dubbo) RPC The infrastructure of microservices

In the picture 6 The meaning of the steps is explained as follows ：

1. The service container is responsible for starting , load , Run the service provider .
2. The service provider at startup , Register your services with the registry .
3. Service consumers at startup , Subscribe to the registry for the services you need .
4. The registry returns a list of service provider addresses to the consumer , If there are changes , The registry pushes the change data to the consumer based on the long connection .
5. Serving consumers , From the provider address list , Based on soft load balancing algorithm , Select a provider to invoke , If the call fails , Select another call .
6. Service consumers and providers , Accumulates the number of calls and the call time in memory , Send statistics to the monitoring center every minute on a regular basis .

Service registry (Service Registry)

Above picture Registry It's the registry , Responsible for service registration and discovery ,Dubbo Before the service system Zookeeper Or your own Registry Realization , and Nacos It's another kind of Registry The implementation of the .

Service registry , It's a service , Examples and metadata databases （Dubbo3 The source data center has been 、 The configuration services are all extracted and independent ）, The service instance is registered to the service registry at startup , And log off on shutdown .

Clients of services and routers query the service registry for available instances of services , The service registry may call the health check of the service instance API To verify that it can handle requests .

Service Metadata (Service Metadata)

Service metadata refers to including service endpoints (endpoints)、 Service Tag 、 Service version number 、 Service instance weight 、 Routing rules 、 Security policy and other data describing the service .

Introduction to logical architecture and its components

• Service management ： Implementation services CRUD, domain name CRUD, Service health check , Service weight management and other functions
• Configuration Management ： Implement configuration management CRUD, version management , Gray management , Monitoring management , Push trajectory , Aggregate data and other functions
• Metadata management ： Provide metadata CURD And marking ability
• Plug-in mechanism ： Realize the ability of three modules to be separated and combined , Implementation extension point SPI Mechanism
• Event mechanism ： Implement asynchronous event notification ,sdk Data change, asynchronous notification, etc
• Log module ： Manage log classification , The level of logging , Log portability （ Especially avoiding conflict ）, Log format , Abnormal code + Help document
• Callback mechanism ：sdk Notification data , Call back the user through a unified mode . Interfaces and data structures need to be scalable
• Addressing mode ： solve ip, domain name ,nameserver、 Broadcast and other addressing modes , Need to be scalable
• Push channel ： solve server With storage 、server between 、server And sdk The problem of inter push performance
• Capacity management ： Manage every tenant , The capacity under the packet , Prevent the storage from being written explosion , Affect service availability
• Traffic management ： According to the tenant , Grouping and other dimensions on the request frequency , Number of long links , Message size , Request flow control to control
• Caching mechanisms ： Disaster recovery Directory , Local cache ,server Caching mechanisms . Disaster recovery directory needs tools
• Boot mode ： In stand-alone mode , Configuration mode , Service mode ,dns Pattern , perhaps all Pattern , Start different programs +UI
• Agreement of conformity ： Solve different data , In the case of different consistency requirements , Different consistency mechanisms
• Storage module ： Solve data persistence 、 Non persistent storage , Solve the problem of data fragmentation
• Nameserver： solve namespace To clusterid The routing problem of , Solve the problem of user environment and nacos Physical environment mapping problem
• CMDB： Solve metadata storage , With the three parties cmdb System docking problem , Solution application , people , Resource relations
• Metrics： Exposure criteria metrics data , It is convenient to connect with the three party monitoring system
• Trace： Exposure criteria trace, Convenience and SLA Get the system through , The journal is white and flat , Push trajectory, etc , And it can connect with the metering and billing system
• Access management ： It's equivalent to Alibaba cloud opening service , Assign identities 、 Capacity 、 Permission process
• User management ： Solve user management , Sign in ,sso Other questions
• Rights management ： Solve identification , Access control , Role management and so on
• Audit system ： Expand the interface to facilitate access to audit systems of different companies
• Notification system ： Core data changes , Or operation , Convenient passage SMS Get the system through , Inform the corresponding person of the data change
• OpenAPI： Exposure criteria Rest style HTTP Interface , Simple and easy to use , Facilitate multilingual Integration
• Console： Easy to use console , Do service management 、 Configuration management and other operations
• SDK： Multilingual sdk
• Agent：dns-f Similar patterns , Or with mesh And so on
• CLI： Command line lightweight management of products , image git As easy to use

Nacos Service registration and discovery

service provider (Service Provider)

Refers to the application side that provides reusable and callable services .

Simulate service registration

The most important thing of service registration is where to register the service , At the registry server , There must be a container for managing services , He keeps instances of all services . You don't need to know the specific implementation details of the container , Just know that there is such a concept .

• Register two instances of the same service to Nacos in ：

• Dual registration mode injection into

• Keep the service online

demo The code is as follows ：

adopt NamingService Interface registerInstance Method to register the service , This method has many overloaded methods , Here we choose a simple one to call . After registration , By calling getAllInstances Method , Get all available instances now , Then let the main thread wait , Print as follows ：

You can find naming The client successfully obtained two instances .

Service consumer (Service Consumer)

After the service is registered in the registry , Consumers of services can carry out the process of service discovery , Consumers can send a request to get a service instance directly to the registry , In this case, the registry will return all available service instances to the consumer , But this is generally not recommended . Another way is for consumers of services to subscribe to a service in the registry , And submit a listener , When the service in the registry changes , The monitor will be notified , At this time, the consumer updates the local service instance list , To ensure that all services are available .

Nacos Consumer service mechanism

It refers to the application party that will initiate a service call . After the service is registered , Service consumers can subscribe to the registry for the services they need , The registry will list all instances of the service “ push ” To the consumer , In fact, the client actively polls to obtain the service , The principle is the same as that for the client to obtain the configuration items of the configuration center .

Now I create a service consumer , Then subscribe to a service in the registry , After receiving the service list returned by the registry , perform 5 Time select Operation of service instance , It is equivalent to a simulated service request , The specific code is shown in the figure below ：

Among them printInstances The main method is to print out the instances of all services , take ServiceConsumer After the class is started , Print out the following logs ：

Nacos Mechanism load balancing

There are many ways to implement load balancing , Including polling method , Random method , Request for ip do hash Post mold taking, etc , From the perspective of load, it can be divided into ： Server load balancing and client load balancing .Nacos After the client of gets the complete instance list of the service , Load balancing algorithm will be performed on the client to obtain an available instance , The pattern uses random access .

Nacos The complete process of service registration and subscription

• Nacos There are two parts for the client to register the service , One is to register the service information to the server , The other is to send heartbeat packets to the server , Both operations are performed through NamingProxy Data interaction with the server .
• Nacos There are also two parts when the client subscribes to the service , One is the regular task of constantly querying available service instances from the server , The other is to constantly take out services from the changed service queue and notify EventListener Holder's scheduled task , Update service subscription list .

Reference material

https://nacos.io/zh-cn/docs/feature-list.html