Access ftp service via other docker container

Question

I have a Golang app, and it is supposed to connect to a FTP Server.

Now, both Golang app and FTP Server is dockerized, but I don't know how to connect to FTP server from Golang app

Here is my docker-compose.yml

version: '2'

services:
  myappgo:
    image: myappgo:exp
    volumes:
      - ./volume:/go
    networks:
      myappgo_network:
    env_file:
      - test.env

  ftpd-server:
    container_name: ftpd-server
    image: stilliard/pure-ftpd:hardened
    ports:
      - "21:21"
      - "30000-30009:30000-30000"
    environment:
      PUBLICHOST: "localhost"
      FTP_USER_NAME: "test"
      FTP_USER_PASS: "test"
      FTP_USER_HOME: "/home/test"
    restart: on-failure
    networks:
      myappgo_network:

networks:
  myappgo_network:

When I run docker compose, all services are up.

I could get IP of ftp container with:

docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' ftpd-server

And then, I installed a ftp client for alpine in my golang container, lftp:

docker exec -it my_app_go sh
apk add lftp
lftp -d ftp://test:test@172.19.0.2 # -d for debug
lftp test@172.19.0.2:~> ls
---- Connecting to 172.19.0.2 (172.19.0.2) port 21
`ls' at 0 [Connecting...]

What am I missing ?

Is the ports line ok? ```- "30000-30009:30000-30000"```` Last 30000 should be 30009, right? — coya, Dec 30 '19 at 18:16

Sergio · Answer 1 · 2019-01-27T21:04:45.273

At least, you need 21/TCP for commands and 20/TCP for data on ftp-server:

ports:
  - "21:21"
  - "20:20"
  - "30000-30009:30000-30009"

I changed your compose-file a little bit:

version: '2'

services:
  myappgo:
    image: alpine:3.8
    tty: true
    networks:
      swarm_default:

  ftpd-server:
    container_name: ftpd-server
    image: stilliard/pure-ftpd:hardened
    ports:
      - "21:21"
      - "20:20"
      - "30000-30009:30000-30009"
    environment:
      PUBLICHOST: "localhost"
      FTP_USER_NAME: "test"
      FTP_USER_PASS: "test"
      FTP_USER_HOME: "/home/test"
    restart: on-failure
    networks:
      swarm_default:

networks:
  swarm_default:

Then I created on ftp-server file /home/test/1 and I can see it from mygoapp-container:

/ # lftp ftp://test:test@172.19.0.2
lftp test@172.19.0.2:/> dir
-rw-r--r--    1 0          0                   0 Jan 22 14:18 1

hi, can you have a quick look at my containerised ftp-server pls? https://stackoverflow.com/questions/64438942/nodejs-application-stops-working-when-containerised?noredirect=1#comment113946483_64438942 — DrkStr, Oct 20 '20 at 10:17

score 4 · Accepted Answer · answered Jan 22 '19 at 14:05

First simplify your dockerfile

version: '3'  # i assume you can migrate to version 3, yes?
services:
  myappgo:
    image: myappgo:exp
    volumes:
      - ./volume:/go
    env_file:
      - test.env
  ftpd-server:
    image: stilliard/pure-ftpd:hardened
    environment:
      PUBLICHOST: "0.0.0.0"
      FTP_USER_NAME: "test"
      FTP_USER_PASS: "test"
      FTP_USER_HOME: "/home/test"
    restart: on-failure

Second, default network is created by docker-compose; no need to do it explicitly. All services get connected to it under their names, so you access them not by ip but by name like ftpd-server

Third, you dont need to expose your ports if you access them from inside. If you need to access them from outside, then you expose.

Next, launch ftp with binding to 0.0.0.0 - binding any tcp service to localhost or 127.0.0.1 makes it accessable only locally.

Last, use service names to connect. Forget about ip addresses and docker inspect. You connection from myappgo to ftp will look like ftp://ftpd-server/foo/bar

Thanks for your help, it worked. I posted another related question here. https://stackoverflow.com/questions/54324387/connecting-ftp-container-works-with-docker-compose-and-not-with-docker-run — Juliatzin, Jan 23 '19 at 09:51
@grapes hi, can you have a quick look at my containerised ftp-server pls? https://stackoverflow.com/questions/64438942/nodejs-application-stops-working-when-containerised?noredirect=1#comment113946483_64438942 — DrkStr, Oct 20 '20 at 10:18
`PUBLICHOST` set to `0.0.0.0` results in FTP with no files for me, set to real host hostname works well. — Dmitry Verhoturov, Jan 11 '21 at 22:17

Access ftp service via other docker container

2 Answers2