Microservices architecture is one of the preferred methods of building scalable and robust applications. It involves breaking large applications into smaller components that are well-defined, performs a specific task and uses sets of application programming interface (API) for their communication.

Communication is an essential part of microservices; it plays an important role in letting services talk to each other within the larger application context. Some examples of protocol microservices use to communicate with each other includes HTTP, gRPC, message brokers, etc.

In this article, we will explore what gRPC is and how to get started by building a user management service using gRPC, MongoDB and Rust.

What is gRPC?

gRPC is a modern communication framework that can run in any environment and helps connect services efficiently. It was introduced in 2015 and governed by the Cloud Native Computing Platform (CNCF). Beyond efficiently connecting services across a distributed system, mobile applications, frontend to backend, etc., it supports health checking, load balancing, tracing, and authentication.

gRPC offers a fresh perspective to developers building medium to complex applications as it can generate client and server bindings for multiple languages. The following are some of its benefits:

Service definition

gRPC uses Protocol Buffers as its interface description language, similar to JSON and provides features like authentication, cancellation, timeouts, etc.

Lightweight and performant

gRPC definitions are 30 percent smaller than JSON definitions and are 5 to 7 times faster than a traditional REST API.

Multiple platform support

gRPC is language agnostic and has automated code generation for client and server-supported languages.

Scalable

From the developer’s environment to production, gRPC is designed to scale millions ler seconds requests.

Getting started

Now that we understand gRPC's importance in building scalable applications, let’s build a user management service with gRPC, MongoDB, and Rust. The project source code can be found here.

Prerequisites

To fully grasp the concepts presented in this tutorial, the following are required:

• Basic understanding of Rust
• Basic understanding of Protocol Buffer
• Protocol Buffer compiler installed
• A MongoDB account to host the database. Signup is completely free.
• Postman or any gRPC testing application

Project and Dependencies setup

To get started, we need to navigate to the desired directory and run the command below in our terminal:

1cargo new grpc_rust && cd grpc_rust

This command creates a Rust project called grpc_rust and navigates into the project directory.

Next, we install the required dependencies by modifying the [dependencies] section of the Cargo.toml file as shown below:

1//other code section goes here
2
3[dependencies]
4tokio = {version = "1", features = ["macros", "rt-multi-thread"]}
5serde = {versiom = "1", features = ["derive"]}
6dotenv = "0.15.0"
7tonic = "0.9.2"
8prost = "0.11.9"
9futures = "0.3"
10
11[dependencies.mongodb]
12version = "2.2.0"
13
14[build-dependencies]
15tonic-build = "0.9.2"

tokio = {version = "1", features = ["macros", "rt-multi-thread"]} is a runtime that enables asynchronous programming in Rust.

serde = {versiom = "1", features = ["derive"]} is a framework for serializing and deserializing Rust data structures.

dotenv = "0.15.0" is a library for managing environment variables.

tonic = "0.9.2" is a Rust implementation of gRPC.

prost = "0.11.9" is a Protocol Buffers implementation in Rust and generates simple, idiomatic Rust code from proto2 and proto3 files.

futures = "0.3" is a library for doing asynchronous programming with MongoDB driver

[dependencies.mongodb] is a driver for connecting to MongoDB. It also specifies the required version and the feature type(Asynchronous API).

[build-dependencies] specifies tonic-build = "0.9.2" as a dependency. It compiles .proto files into Rust code.

Defining the user management Protocol Buffer and compilation

To get started, we need to define a Protocol Buffer to represent all the operations and responses involved in the user management service. To do this, first, we need to create a proto folder in the root directory, and in this folder, create a user.proto file and add the snippet below:

1syntax = "proto3";
2package user;
3
4service UserService {
5    rpc GetUser (UserRequest) returns (UserResponse);
6    rpc CreateUser (CreateUserRequest) returns (CreateUserResponse);
7    rpc UpdateUser (UpdateUserRequest) returns (UpdateUserResponse);
8    rpc DeleteUser (DeleteUserRequest) returns (DeleteUserResponse);
9    rpc GetAllUsers (Empty) returns (GetAllUsersResponse);
10}
11
12message UserRequest {
13    string id = 1;
14}
15
16message UserResponse {
17    string id = 1;
18    string name = 2;
19    string location = 3;
20    string title = 4;
21}
22
23message CreateUserRequest {
24    string name = 2;
25    string location = 3;
26    string title = 4;
27}
28
29message CreateUserResponse {
30    string data = 1;
31}
32
33message UpdateUserRequest {
34    string _id = 1;
35    string name = 2;
36    string location = 3;
37    string title = 4;
38}
39
40message UpdateUserResponse {
41    string data = 1;
42}
43
44message DeleteUserRequest {
45    string id = 1;
46}
47
48message DeleteUserResponse {
49    string data = 1;
50}
51
52message Empty {}
53
54message GetAllUsersResponse {
55    repeated UserResponse users = 1;
56}

The snippet above does the following:

• Specifies the use of proto3 syntax
• Declares user as the package name
• Creates a service to Create, Read, Edit, and Delete (CRUD) a user and their corresponding responses as messages.

Secondly, we need to create a build file that instructs tonic-build = "0.9.2" dependency to compile our user.proto file into a Rust code. To do this, we need to create a build.rs file in the root directory and add the snippet below:

1fn main() -> Result<(), Box<dyn std::error::Error>> {
2    tonic_build::compile_protos("proto/user.proto")?;
3    Ok(())
4}

Lastly, we need to compile the user.proto file using the build.rs instruction we specified earlier by running the command below in our terminal:

1cargo build

Using the generated code from gRPC in our application

With the build process done, we can start using the generated code in our application.

Database setup and integration

First, we need to set up a database and a collection on MongoDB as shown below:

We also need to get our database connection string by clicking on the Connect button and changing the Driver to Rust.

Secondly, we must modify the copied connection string with the user's password we created earlier and change the database name. To do this, we need to create a .env file in the root directory and add the snippet copied:

1MONGOURI=mongodb+srv://<YOUR USERNAME HERE>:<YOUR PASSWORD HERE>@cluster0.e5akf.mongodb.net/<DATABASE NAME>?retryWrites=true&w=majority

Sample of a properly filled connection string below:

1MONGOURI=mongodb+srv://malomz:malomzPassword@cluster0.e5akf.mongodb.net/rustDB?retryWrites=true&w=majority

Lastly, we need to navigate to the src folder, create a mongo_connection.rs file to implement our database logic and add the snippet below:

1use std::{env, io::Error};
2
3use dotenv::dotenv;
4use futures::TryStreamExt;
5use mongodb::bson::doc;
6use mongodb::bson::oid::ObjectId;
7use mongodb::results::{DeleteResult, InsertOneResult, UpdateResult};
8use mongodb::{Client, Collection};
9use serde::{Deserialize, Serialize};
10
11#[derive(Debug, Serialize, Deserialize)]
12pub struct User {
13    #[serde(rename = "_id", skip_serializing_if = "Option::is_none")]
14    pub id: Option<ObjectId>,
15    pub name: String,
16    pub location: String,
17    pub title: String,
18}
19
20pub struct DBMongo {
21    col: Collection<User>,
22}
23
24impl DBMongo {
25    pub async fn init() -> Self {
26        dotenv().ok();
27        let uri = match env::var("MONGOURI") {
28            Ok(v) => v.to_string(),
29            Err(_) => format!("Error loading env variable"),
30        };
31        let client = Client::with_uri_str(uri)
32            .await
33            .expect("error connecting to database");
34        let col = client.database("rustDB").collection("User");
35        DBMongo { col }
36    }
37
38    pub async fn create_user(new_user: User) -> Result<InsertOneResult, Error> {
39        let db = DBMongo::init().await;
40        let new_doc = User {
41            id: None,
42            name: new_user.name,
43            location: new_user.location,
44            title: new_user.title,
45        };
46        let user = db
47            .col
48            .insert_one(new_doc, None)
49            .await
50            .ok()
51            .expect("Error creating user");
52        Ok(user)
53    }
54
55    pub async fn get_user(id: String) -> Result<User, Error> {
56        let db = DBMongo::init().await;
57        let obj_id = ObjectId::parse_str(id).unwrap();
58        let filter = doc! {"_id": obj_id};
59        let user_detail = db
60            .col
61            .find_one(filter, None)
62            .await
63            .ok()
64            .expect("Error getting user's detail");
65        Ok(user_detail.unwrap())
66    }
67
68    pub async fn update_user(id: String, new_user: User) -> Result<UpdateResult, Error> {
69        let db = DBMongo::init().await;
70        let obj_id = ObjectId::parse_str(id).unwrap();
71        let filter = doc! {"_id": obj_id};
72        let new_doc = doc! {
73            "$set":
74                {
75                    "id": new_user.id,
76                    "name": new_user.name,
77                    "location": new_user.location,
78                    "title": new_user.title
79                },
80        };
81        let updated_doc = db
82            .col
83            .update_one(filter, new_doc, None)
84            .await
85            .ok()
86            .expect("Error updating user");
87        Ok(updated_doc)
88    }
89
90    pub async fn delete_user(id: String) -> Result<DeleteResult, Error> {
91        let db = DBMongo::init().await;
92        let obj_id = ObjectId::parse_str(id).unwrap();
93        let filter = doc! {"_id": obj_id};
94        let user_detail = db
95            .col
96            .delete_one(filter, None)
97            .await
98            .ok()
99            .expect("Error deleting user");
100        Ok(user_detail)
101    }
102
103    pub async fn get_all_users() -> Result<Vec<User>, Error> {
104        let db = DBMongo::init().await;
105        let mut cursors = db
106            .col
107            .find(None, None)
108            .await
109            .ok()
110            .expect("Error getting list of users");
111        let mut users: Vec<User> = Vec::new();
112        while let Some(user) = cursors
113            .try_next()
114            .await
115            .ok()
116            .expect("Error mapping through cursor")
117        {
118            users.push(user)
119        }
120        Ok(users)
121    }
122}

The snippet above does the following:

• Line: 1 - 9: Imports the required dependencies
• Line: 11 - 18: Creates a User struct with required properties. We also added field attributes to the id property to rename and ignore the field if it is empty.
• Line: 20 - 22: Creates a DBMongo struct with a col field to access MongoDB collection
• Line: 24 - 122: Creates an implementation block that adds methods to the MongoRepo struct to initialize the database with its corresponding CRUD operation.

Integrating the database logic with gRPC-generated code

With our database logic setup, we can use the methods to create our application handlers. To do this, we need to create a service.rs file inside the same src folder and add the snippet below:

1use mongodb::bson::oid::ObjectId;
2use tonic::{Request, Response, Status};
3use user::{
4    user_service_server::UserService, CreateUserRequest, CreateUserResponse, DeleteUserRequest,
5    DeleteUserResponse, Empty, GetAllUsersResponse, UpdateUserRequest, UpdateUserResponse,
6};
7use crate::mongo_connection::{self, DBMongo};
8use self::user::{UserRequest, UserResponse};
9
10pub mod user {
11    tonic::include_proto!("user");
12}
13
14#[derive(Debug, Default)]
15pub struct User {}
16
17#[tonic::async_trait]
18impl UserService for User {
19    async fn create_user(
20        &self,
21        request: Request<CreateUserRequest>,
22    ) -> Result<Response<CreateUserResponse>, Status> {
23        let req = request.into_inner();
24        let new_user = mongo_connection::User {
25            id: None,
26            name: req.name,
27            location: req.location,
28            title: req.title,
29        };
30        let db = DBMongo::create_user(new_user).await;
31        match db {
32            Ok(resp) => {
33                let user = CreateUserResponse {
34                    data: resp.inserted_id.to_string(),
35                };
36                Ok(Response::new(user))
37            }
38            Err(error) => Err(Status::aborted(format!("{}", error))),
39        }
40    }
41
42    async fn get_user(
43        &self,
44        request: Request<UserRequest>,
45    ) -> Result<Response<UserResponse>, Status> {
46        let req = request.into_inner();
47        let db = DBMongo::get_user(req.id).await;
48        match db {
49            Ok(resp) => {
50                let user = UserResponse {
51                    id: resp.id.unwrap().to_string(),
52                    name: resp.name,
53                    location: resp.location,
54                    title: resp.title,
55                };
56                Ok(Response::new(user))
57            }
58            Err(error) => Err(Status::aborted(format!("{}", error))),
59        }
60    }
61
62    async fn update_user(
63        &self,
64        request: Request<UpdateUserRequest>,
65    ) -> Result<Response<UpdateUserResponse>, Status> {
66        let req = request.into_inner();
67        let new_user = mongo_connection::User {
68            id: Some(ObjectId::parse_str(req.id.clone()).unwrap()),
69            name: req.name,
70            location: req.location,
71            title: req.title,
72        };
73        let db = DBMongo::update_user(req.id.clone(), new_user).await;
74        match db {
75            Ok(_) => {
76                let user = UpdateUserResponse {
77                    data: String::from("User details updated successfully!"),
78                };
79                Ok(Response::new(user))
80            }
81            Err(error) => Err(Status::aborted(format!("{}", error))),
82        }
83    }
84
85    async fn delete_user(
86        &self,
87        request: Request<DeleteUserRequest>,
88    ) -> Result<Response<DeleteUserResponse>, Status> {
89        let req = request.into_inner();
90        let db = DBMongo::delete_user(req.id).await;
91        match db {
92            Ok(_) => {
93                let user = DeleteUserResponse {
94                    data: String::from("User details deleted successfully!"),
95                };
96                Ok(Response::new(user))
97            }
98            Err(error) => Err(Status::aborted(format!("{}", error))),
99        }
100    }
101
102    async fn get_all_users(
103        &self,
104        _: Request<Empty>,
105    ) -> Result<Response<GetAllUsersResponse>, Status> {
106        let db = DBMongo::get_all_users().await;
107        match db {
108            Ok(resp) => {
109                let mut user_list: Vec<UserResponse> = Vec::new();
110                for data in resp {
111                    let mapped_user = UserResponse {
112                        id: data.id.unwrap().to_string(),
113                        name: data.name,
114                        location: data.location,
115                        title: data.title,
116                    };
117                    user_list.push(mapped_user);
118                }
119                let user = GetAllUsersResponse { users: user_list };
120                Ok(Response::new(user))
121            }
122            Err(error) => Err(Status::aborted(format!("{}", error))),
123        }
124    }
125}

The snippet above does the following:

• Line: 1 - 8: Imports the required dependencies (including the gRPC-generated)
• Line: 10 - 12: Declares user struct to bring into scope our gRPC-generated code using tonic::include_proto!("user")
• Line: 14 - 15: Creates a User struct to represent our application model
• Line: 17 - 125: Implements the UserService traits from the gRPC-generated code for the User struct by creating required methods and returning appropriate responses as generated by gRPC

Creating the server

With that done, we can create the application gRPC server by modifying the main.rs file as shown below:

1use std::net::SocketAddr;
2
3use service::{user::user_service_server::UserServiceServer, User};
4use tonic::transport::Server;
5
6mod mongo_connection;
7mod service;
8
9#[tokio::main]
10async fn main() -> Result<(), Box<dyn std::error::Error>> {
11    let address: SocketAddr = "[::1]:8080".parse().unwrap();
12    let user = User::default();
13
14    Server::builder()
15        .add_service(UserServiceServer::new(user))
16        .serve(address)
17        .await?;
18    Ok(())
19}

The snippet above does the following:

• Imports the required dependencies and adds the mongo_connection and service as a module
• Creates a server using Server::builder() method and adds the UserServiceServer as a service.

With that done, we can test our application by running the command below in our terminal.

1cargo run

Testing with Postman

With our server up and running, we can test our application by creating a new gRPC Request.

Input grpc://[::1]:8080 as the URL, select the Import a .proto file option and upload the user.proto file we created earlier.

With that done, the corresponding method will be populated and we can test them accordingly.

We can also validate that our gRPC server works by checking our MongoDB collection

Conclusion

This post discussed what gRPC is, its role in building scalable applications and how to get started by building a user management service with Rust and MongoDB. Beyond what was discussed above, gRPC offers robust techniques around authentication, error handling, performance, etc.

These resources might be helpful:

• Tonic
• Tokio runtime
• MongoDB Rust driver
• Serde (Serializing and Deserializing library)