Angular proxy to backend is not working

In the Angular app, We often talk to backend servers in the development phase, we will explore all the scenarios in this article. Here are the topics we cover.

• What is proxying
• Example Project
• proxy.config.json options
• Proxy Setup with Angular CLI
• Different Ways to configure
• Rewrite the Path URL
• Multiple app entries to one API endpoint
• Multiple app entries with multiple endpoints
• Summary

What is proxying

In general, A proxy or proxy server serves as a gateway between your app and the internet. It’s an intermediate server between client and servers by forwarding client requests to resources.

In Angular, we often use this proxying in the development environment. Angular uses webpack dev server to serve the app in development mode. If we look at the following diagram, app UI is running on port 4200 and backend server is running on port 3700. All the calls start with /api will be redirected to the backend server and rest all fall back to the same port.

In subsequent sections, we will see how we can accomplish this and other options as well.

proxying all URLs start with /api

Example Project

Let’s follow these commands for the example project and you are ready for angular CLI proxy setup.

//clone the project
git clone https://github.com/bbachi/angular-proxy-example
// install dependencies for node server
npm install
//cd to ui
cd appui
// install app ui dependencies
np install

Once you install all the dependencies, you can start both Angular app and node js server on 4200 and 3070 respectively.

You can start the Angular app with these commands npm start or ng serveand here is the Angular app running on 4200.

Let’s start the server with this command npm start and test this API on port 3070.

proxy.config.json options

target: This is where we need to define the backend URL.

pathRewrite: We need to use this option to edit or rewrite the path

changeOrigin: If your backend API is not running on localhost, we need to make this flag true.

logLevel: If you want to check whether proxy configuration working properly or not, this flag should be debug.

bypass: Sometimes we have to bypass the proxy, we can define a function with this. But it should define in proxy.config.js instead of proxy.config.json.

Proxy Setup with Angular CLI

Now app and server running on different ports. Let’s set up a proxy for communication between these.

First thing you need is this proxy.config.json. We are defining the target for all the URLs starts with /api here.

{
	    "/api/*": {
	    "target": "http://localhost:3070",
	    "secure": false,
	    "logLevel": "debug",
	    "changeOrigin": true
	  }
	}

proxy.config.json

Second thing is to let Angular know we have this proxy.config.json in place. We can do that by adding the proxy-config flag while starting the app like below. Once started, we can see the message indicating all the URLs starting with /api will be redirecting to nodejs server running on port 3070.

npm start script

Now we can test the app and see the settings from the server

settings coming from the server

Different Ways to configure

Another way to configure proxy config in the Angular project is defining in angular.json.

proxyConfig in angular.json

Let’s summarize the ways here

• Add this ng serve — proxy-config proxy.conf.json to the start script in package.json
• Define in angular.json under serve section like above.

Rewrite the Path URL

Whenever there is a change in the URLs, we often rewrite the path of the backend servers endpoints. We can do that with the pathRewrite.

Let’s understand the pathRewrite option. For instance, our backend URL /api/settings is changed to /api/app/settings and we want to test in development before it goes to production. We can achieve this with the option pathRewrite like below.

{
	    "/api/*": {
	    "target": "http://localhost:3070",
	    "secure": false,
	    "logLevel": "debug",
	    "changeOrigin": true,
	    "pathRewrite": {
	      "^/api/settings": "/api/app/settings",
	      "^/api": ""
	    }
	  }
	}

app.get('/api/app/settings', (req,res) => {
	    console.log('--settings---');
	    res.json(settings)
	})
app.get('/users', (req,res) => {
  console.log('--users---');
  res.json({users:[]})
})

path rewriting

So, we are rewriting /api/setting to /api/app/settings and /api/users to /users.

Here is the console output while starting the app.

angular proxy rewriting URL paths

Multiple app entries to one API endpoint

Sometimes we have multiple modules with services in our app. We might have a scenario where multiple entries or services will call the same API endpoint.

In that case, we need to define proxy.config.js instead of proxy.config.json. Don’t forget to add that to angular.json.

const PROXY_CONFIG = [

{

context: [

“/userapi”,

“/settingsapi”,

“/productapi”,

],

target: “http://localhost:3070”,

secure: false

}

]

module.exports = PROXY_CONFIG;

proxy.config.js

angular.json

Multiple app entries with multiple endpoints

We have seen how to define multiple entries to the same endpoint. Let’s look at multiple entries to multiple endpoints scenario.

proxy for multiple APIs

For instance, we have three APIs running on ports 3700, 3800 and 3900 and your APP should talk to these APIs.

All we need to add multiple entries to the proxy.config.json. Here is the configuration for that setup and we have to make sure all APIs are running on these ports for successful communication.

{

“/user/": {

“target”: “http://localhost:3700”,

“secure”: false,

“logLevel”: “debug”

},

"/product/”: {

“target”: “http://localhost:3800”,

“secure”: false,

“logLevel”: “debug”

},

“/settings/*”: {

“target”: “http://localhost:3900”,

“secure”: false,

“logLevel”: “debug”

}

}

proxy.config.json

Summary

• In Angular, the proxy is used mostly in the development environment to facilitate the communication between server and UI.
• We need to have a backend server and UI running on different ports.
• Proxy.config.json is the file which holds all the information regarding backend API URLs.
• We need to make sure the Angular App and Backends are running on different ports for successful communication.
• There are two ways to configure one is to add in the angular.json and another is adding a proxy-config flag to the start script.
• We can rewrite the path with the option pathRewrite.
• We can proxy multiple entries to one backend API with the proxy.config.js.
• We can proxy multiple entries to multiple backends as well.

Thanks for reading…

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Angular is a TypeScript based framework that works in synchronization with HTML, CSS, and JavaScript. To work with angular, domain knowledge of these 3 is required.

1. Installing Node.js and npm
2. Installing Angular CLI
3. Creating workspace
4. Deploying your First App

In this article, you will get to know about the Angular Environment setup process. After reading this article, you will be able to install, setup, create, and launch your own application in Angular. So let’s start!!!

Install Angular in Easy Steps

For Installing Angular on your Machine, there are 2 prerequisites:

• Node.js
• npm Package Manager

Node.js

First you need to have Node.js installed as Angular require current, active LTS or maintenance LTS version of Node.js

Download and Install Node.js version suitable for your machine’s operating system.

Npm Package Manager

Angular, Angular CLI and Angular applications are dependent on npm packages. By installing Node.js, you have automatically installed the npm Package manager which will be the base for installing angular in your system. To check the presence of npm client and Angular version check of npm client, run this command:

1. npm -v

Installing Angular CLI

• Open Terminal/Command Prompt
• To install Angular CLI, run the below command:

1. npm install -g @angular/cli

· After executing the command, Angular CLI will get installed within some time. You can check it using the following command

1. ng --version

Workspace Creation

Now as your Angular CLI is installed, you need to create a workspace to work upon your application. Methods for it are:

• Using CLI
• Using Visual Studio Code

1. Using CLI

To create a workspace:

• Navigate to the desired directory where you want to create your workspace using cd command in the Terminal/Command prompt
• Then in the directory write this command on your terminal and provide the name of the app which you want to create. In my case I have mentioned DataFlair:

1. Ng new YourAppName

• After running this command, it will prompt you to select from various options about the CSS and other functionalities.

• To leave everything to default, simply press the Enter or the Return key.

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Angular is a Typescript-based open-source front-end web application platform. The Angular Team at Google and a community of individuals and corporations lead it. Angular lets you extend HTML’s syntax to express your apps’ components clearly. The angular resolves challenges while developing a single page and cross-platform applications. So, here the meaning of the single-page applications in angular is that the index.html file serves the app. And, the index.html file links other files to it.

We build angular applications with basic concepts which are NgModules. It provides a compilation context for components. At the beginning of an angular project, the command-line interface provides a built-in component which is the root component. But, NgModule can add a number of additional components. These can be created through a template or loaded from a router. This is what a compilation context about.

What is a Component in Angular?

Components are key features in Angular. It controls a patch of the screen called a view. A couple of components that we create on our own helps to build a whole application. In the end, the root component or the app component holds our entire application. The component has its business logic that it does to support the view inside the class. The class interacts with the view through an API of properties and methods. All the components added by us in the application are not linked to the index.html. But, they link to the app.component.html through the selectors. A component can be a component and not only a typescript class by adding a decorator @Component. Then, for further access, a class can import it. The decorator contains some metadata like selector, template, and style. Here’s an example of how a component decorator looks like:

@Component({
    selector: 'app-root',
    templateUrl: 'app.component.html',
    styleUrls: ['app.component.scss']
})

Role of App Module

Modules are the package of functionalities of our app. It gives Angular the information about which features does my app has and what feature it uses. It is an empty Typescript class, but we transform it by adding a decorator @NgModule. So, we have four properties that we set up on the object pass to @NgModule. The four properties are declarations, imports, providers, and bootstrap. All the built-in new components add up to the declarations array in @NgModule.

@NgModule({
declarations: [
  AppComponent,
],
imports: [
  BrowserModule,
  HttpClientModule,
  AppRoutingModule,
  FormsModule
],
bootstrap: [AppComponent]
})

What is Data Binding?

Data Binding is the communication between the Typescript code of the component and the template. So, we have different kinds of data binding given below:

• When there is a requirement to output data from our Typescript code in the HTML template. String interpolation handles this purpose like {{data}} in HTML file. Property Binding is also used for this purpose like [property] = “data”.
• When we want to trigger any event like clicking a button. Event Binding works while we react to user events like (event) = “expression”.
• When we can react to user events and output something at the same time. Two-way Binding is used like [(ngModel)] = “data”.

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Please watch this video. I hope this video would be helpful for you to understand it and use it in your projects

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