NodeJS application stops working when containerised [FTP server in a container]

Question

I am trying to containerise an ftp server NodeJS application. It works fine when I run it with npm but it does not respond when I run it inside of a container.

This is the node app: The src/index.js file

const FtpSvr = require ( 'ftp-srv' );

const hostname = '127.0.0.1';
const port = 21;

const ftpServer = new FtpSvr ({
url:`ftp://${hostname}:${port}`,
anonymous:true
} );

ftpServer.on('login', ({connection, username, password}, resolve, reject) =>
{
    resolve({root : "./"})

    connection.on('STOR', (error, fileName) => {
        console.log("STOR")
    });
});

ftpServer.on ( 'client-error', (connection, context, error) =>
{
    console.log ( `error: ${error}` );
});

ftpServer.listen().then(() => {console.log(`Server running at http://${hostname}:${port}/`);});

my package.json file

{
  "name": "ftp-server",
  "version": "1.0.0",
  "description": "FTP server to receive images from cameras and save them on Azure Blob storage",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "start": "node src/index.js"
  },
  "author": "Rakshak",
  "license": "ISC",
  "dependencies": {
    "ftp-srv": "4.3.4"
  }
}

my docker file

FROM node:12

WORKDIR /app

COPY package.json ./

RUN npm install

COPY . .

EXPOSE 20-21
EXPOSE 65500-65515

CMD ["npm", "start"]

I am testing the FTP server using FileZilla. When I run the server using npm start and connect using FileZilla

Connecting to 127.0.0.1:5000...
Status:         Connection established, waiting for welcome message...
Status:         Insecure server, it does not support FTP over TLS.
Status:         Logged in
Status:         Retrieving directory listing...
Status:         Directory listing of "/" successful

I am using this command to build the docker image

 docker build -t rrakshak/ftp-demo .

And I am using this to run the docker

 docker run -p 5000:5000 rrakshak/ftp-demo:latest

This is the message on the FileZilla console

Connecting to 127.0.0.1:5000...
Status:         Connection established, waiting for welcome message...
Error:          Connection closed by server
Error:          Could not connect to server
Status:         Waiting to retry...
Status:         Connecting to 127.0.0.1:5000...
Status:         Connection established, waiting for welcome message...
Error:          Connection closed by server
Error:          Could not connect to server

It looks like when the server is running inside of a container the FileZilla is able to connect but is not receiving the file listing response it expects.

------------Update-----------------------

setting the host to 0.0.0. give me a new set of messages on Filezilla

Status:         Connecting to 127.0.0.1:21...
Status:         Connection established, waiting for welcome message...
Status:         Insecure server, it does not support FTP over TLS.
Status:         Logged in
Status:         Retrieving directory listing...
Command:    PWD
Response:   257 "/"
Command:    TYPE I
Response:   200 Switch to "binary" transfer mode.
Command:    PASV
Response:   502 Command not supported
Command:    PORT 127,0,0,1,231,209
Response:   500 The given address is not yours
Error:          Failed to retrieve directory listing

Why does my app work when I run it in node but not when I containerise it?

Answer 1

Listen on 0.0.0.0:5000 in the container, with passive ports defined

const FtpSvr = require ( 'ftp-srv' );
  
const hostname = '0.0.0.0';
const port = 5000;

const ftpServer = new FtpSvr ({
  url: `ftp://${hostname}:${port}`,
  anonymous: true,
  pasv_url: `ftp://${hostname}:${port}`,
  pasv_min: 65500,
  pasv_max: 65515,
});

Build the container as is and then run with the following ports mapped, which can all be used in an ftp connection:

docker run -p 5000:5000 -p 65500-65515:65500-65515 --rm rrakshak/ftp-demo

Gives the response:

$ curl ftp://localhost:5000
-rw-r--r-- 1 1 1          141 Oct 21 01:22 Dockerfile
drwxr-xr-x 1 1 1         4096 Oct 21 01:21 node_modules
-rw-r--r-- 1 1 1        21137 Oct 21 01:21 package-lock.json
-rw-r--r-- 1 1 1           52 Oct 21 01:21 package.json
-rw-r--r-- 1 1 1          660 Oct 21 01:23 server.js
-rw-r--r-- 1 1 1        20287 Oct 21 01:21 yarn.lock

The ftp client must be set to use passive mode.

When an FTP client is in active mode, the FTP server receives a PORT command from the client and creates a new TCP connection from the container back out to the client for data on that PORT.

Due to the Docker port mapping into the container, the source address of this data connection often won't match what the FTP client is using as the initial destination for the FTP server. Similar issues occur when setting up FTP servers behind NAT on classic servers.

Answer 2

Try binding to 0.0.0.0. As you are running inside Docker, it will not work to bind against 127.0.0.1, as the request will come from outside (at least, from the perspective of the Docker container).

For hints on troubleshooting these kind of network issues, you can find some ideas in the answer to this related question.