How to deal with a HTTP POST method status code 404 (Not Found)?

Question

am running some docker containers inside a virtual machine. As I come to understand, each docker container has a different ip, as well as the virtual machine itself of course. When trying to run a web-app on my local host machine, I access the page http://<vm's_ip_address>:3000.

When attempting to execute an action in this web app, the following error occurs: POST http://83.212.117.117/websites/evaluate 404 (Not Found)

The error happens on the handleSubmit(event) method of the following ResultPageDisplay file:

`handleSubmit(event) { event.preventDefault()

this.setState({statusCode: 2})

API.post(`websites/evaluate`, { url: this.state.userInput})
  .then(res => {
     let score = res.data.score
     let url = res.data.url
     let imageURI = res.data.image

     // DEBUGGING PURPOSES
     // console.log(res.data)

     this.setState({result: {
       score: score,
       url: url,
       imageURI: imageURI
     }})
     this.setState({statusCode: 3})
  })
  .catch(err => {
    let failedURL = this.state.userInput
    this.setState({result: {
      score: null,
      url: failedURL,
      imageURI: null
    }})
    let status = err.response.status

    // DEBUGGING PURPOSES
    // console.log(status)

    this.setState({statusCode: 4})

    if (status === 500) {
      this.setState({
        statusCode: 5
      })
    }

  })

}`

I am suspecting that the problem lies somewhere in the configuration files, like nginx.conf. I am also wondering if there is something wrong with some other file like server.js or api.js.

I tried modifying these files, by creating a reverse proxy to map the ports correctly, but I do not understand the whole concept pretty well and maybe I was doing it not correctly. My nginx.conf file is the following:

`upstream app {
    server client:3000;
}

server {
    listen 80;
    server_name localhost;

    location / {
        proxy_pass http://app;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
    }
}`