Access ftp service via other docker container - docker

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 ?

Answer 1

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

Answer 2

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