Docker Port Forwarding stops working after a while

Question

I am experiencing an intermittent issue with accessing my Docker containers from external networks. After restarting the Docker service, the containers become accessible from outside the network, but after some time, they can no longer be reached externally. However, throughout this period, all containers remain accessible from the host machine. I would appreciate your assistance in resolving this matter.

Issue Description

• Docker containers initially become accessible externally after restarting the Docker service
• After an unspecified duration, external access to these containers is lost, although they remain accessible from the host machine (verified using curl -X GET http://{{machine-ip-addr}}:80)
• Confirmed via tcpdump that network interface eth0 is receiving traffic on ports 80 and 443.
• UFW is disabled, ruling it out as the cause of the issue.
• No recent changes in Docker configuration or network settings correspond with the issue onset.
• Verified Docker container configuration; necessary ports are exposed.
• The docker-compose file is structured like this simplified version:

version: '3.3'
services:
  l-app:
    restart: always
    image: s-h-l/l-app:1.0.0
    volumes:
      - shared-volume:/tmp
    ports:
      - 80:8080
volumes:
    shared-volume:

Checked iptables rules; found no rules blocking the relevant ports

Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy DROP)
target     prot opt source               destination
DOCKER-USER  all  --  anywhere             anywhere
DOCKER-ISOLATION-STAGE-1  all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere             ctstate RELATED,ESTABLISHED
DOCKER     all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere             ctstate RELATED,ESTABLISHED
DOCKER     all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

Chain DOCKER (2 references)
target     prot opt source               destination
ACCEPT     tcp  --  anywhere             172.18.0.2           tcp dpt:http-alt
ACCEPT     tcp  --  anywhere             172.18.0.3           tcp dpt:http
ACCEPT     tcp  --  anywhere             172.18.0.5           tcp dpt:postgresql
ACCEPT     tcp  --  anywhere             172.18.0.4           tcp dpt:http-alt

Chain DOCKER-ISOLATION-STAGE-1 (1 references)
target     prot opt source               destination
DOCKER-ISOLATION-STAGE-2  all  --  anywhere             anywhere
DOCKER-ISOLATION-STAGE-2  all  --  anywhere             anywhere
RETURN     all  --  anywhere             anywhere

Chain DOCKER-ISOLATION-STAGE-2 (2 references)
target     prot opt source               destination
DROP       all  --  anywhere             anywhere
DROP       all  --  anywhere             anywhere
RETURN     all  --  anywhere             anywhere

Chain DOCKER-USER (1 references)
target     prot opt source               destination
RETURN     all  --  anywhere             anywhere

Environment Details

• Host Operating System: 5.4.0-167-generic #184-Ubuntu 20.04 LTS
• Docker Version: 24.0.7
• Docker-Compose Version: 1.25.0

The intermittent nature of the issue, particularly its correlation with restarting the Docker service, suggests a potential problem with network routing or external firewall settings beyond the host machine. Your insights or guidance on this matter would be greatly appreciated. Thank you for your assistance.