I have actually a worse problem, my socat is running fine, but I am unable to telnet 172.17.0.1 1026 or 172.17.0.2 1026 either. Also tried 127.0.0.1 1026 and 1025, all failed from within the docker container with Discourse.
I can connect with telnet just fine on the host machine with 127.0.0.1 1025 did Discourse change something?
root@raspberry:/var/discourse# sudo systemctl status protonsocat.service
● protonsocat.service - Socat Bridge ProtonMail/Discourse
Loaded: loaded (/etc/systemd/system/protonsocat.service; enabled; vendor preset: enabled)
Active: active (running) since Sat 2023-02-25 20:37:34 CET; 4min 37s ago
Main PID: 1530542 (socat)
Tasks: 1 (limit: 9236)
Memory: 816.0K
CPU: 10ms
CGroup: /system.slice/protonsocat.service
└─1530542 socat -d -d -lm TCP4-LISTEN:1026,fork,reuseaddr,so-bindtodevice=docker0,range=172.17.0.0/24 TCP4:127.0.0.1:1025
Feb 25 20:37:34 raspberry.local systemd[1]: Started Socat Bridge ProtonMail/Discourse.
Feb 25 20:37:34 raspberry.local socat[1530542]: 2023/02/25 20:37:34 socat[1530542] W ioctl(5, IOCTL_VM_SOCKETS_GET_LOCAL_CID, ...): Inappropriate ioctl for device
Feb 25 20:37:34 raspberry.local socat[1530542]: N listening on AF=2 0.0.0.0:1026
Host machine:
root@raspberry:/var/discourse# telnet 127.0.0.1 1025
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
220 127.0.0.1 ESMTP Service Ready
root@raspberry:/var/discourse# nmap 127.0.0.1 1025
Starting Nmap 7.80 ( https://nmap.org ) at 2023-02-25 21:03 CET
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000045s latency).
Not shown: 993 closed ports
PORT STATE SERVICE
80/tcp open http
443/tcp open https
1025/tcp open NFS-or-IIS
3306/tcp open mysql
5432/tcp open postgresql
8080/tcp open http-proxy
8088/tcp open radan-http
Nmap done: 2 IP addresses (1 host up) scanned in 3.36 seconds
My interfaces on host:
root@raspberry:/var/discourse# ifconfig
br-eb8fd6a0d930: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.18.0.1 netmask 255.255.0.0 broadcast 172.18.255.255
inet6 fe80::42:bdff:fe5c:8dbf prefixlen 64 scopeid 0x20<link>
ether 02:42:bd:5c:8d:bf txqueuelen 0 (Ethernet)
RX packets 1336 bytes 94913 (94.9 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 2254 bytes 3098019 (3.0 MB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
docker0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.17.0.1 netmask 255.255.0.0 broadcast 172.17.255.255
inet6 fe80::42:60ff:feaf:784c prefixlen 64 scopeid 0x20<link>
ether 02:42:60:af:78:4c txqueuelen 0 (Ethernet)
RX packets 295920 bytes 21547471 (21.5 MB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 1049936 bytes 1487623390 (1.4 GB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
eth0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether dc:a6:32:c2:70:f8 txqueuelen 1000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1000 (Local Loopback)
RX packets 97179 bytes 22606251 (22.6 MB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 97179 bytes 22606251 (22.6 MB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
veth5a26573: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet6 fe80::428:bfff:febf:cf5c prefixlen 64 scopeid 0x20<link>
ether 06:28:bf:bf:cf:5c txqueuelen 0 (Ethernet)
RX packets 1336 bytes 113617 (113.6 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 2279 bytes 3099825 (3.0 MB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
vethe0f8588: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet6 fe80::a04d:adff:feb1:351a prefixlen 64 scopeid 0x20<link>
ether a2:4d:ad:b1:35:1a txqueuelen 0 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 32 bytes 2488 (2.4 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
vethfe706a1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet6 fe80::74b3:3aff:feea:89ec prefixlen 64 scopeid 0x20<link>
ether 76:b3:3a:ea:89:ec txqueuelen 0 (Ethernet)
RX packets 4459 bytes 287499 (287.4 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 5221 bytes 7330834 (7.3 MB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
wlan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 10.0.0.4 netmask 255.255.255.0 broadcast 10.0.0.255
inet6 fe80::dea6:32ff:fec2:70f9 prefixlen 64 scopeid 0x20<link>
ether dc:a6:32:c2:70:f9 txqueuelen 1000 (Ethernet)
RX packets 2789702 bytes 3447696344 (3.4 GB)
RX errors 0 dropped 7 overruns 0 frame 0
TX packets 1082661 bytes 213831559 (213.8 MB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
Docker
root@raspberry-app:/var/www/discourse# telnet 172.17.0.1 1026
Trying 172.17.0.1...
telnet: Unable to connect to remote host: Connection refused