Launching Multiple Docker Containers using Ansible - docker

Question

I am trying to build an image and trying to launch multiple docker containers using ansible playbook. I am not able to understand how do i publish the ports. The below playbook gives me an error which is quite obvious that the port is already allocated but then how do i achieve this because from outside the containers there will only be one port right to acces all the containers?
Playbook -
- name: Manage Docker instances via Ansible
hosts: shashank-VM
connection: local
become: yes
become_method: sudo
tasks:
- name: Building an image from Dockerfile
docker_image:
build:
path: .
pull: yes
name: web_new
source: build
- name: Creation of Docker Containers
docker_container:
name: my-app-{{ item }}
image: web_new
state: present
ports:
- "79:80"
with_sequence: count=3
- name: Starting Docker Containers
docker_container:
name: my-app-{{ item }}
image: web_new
state: started
with_sequence: count=3
Error -
changed: [shashank-VM]
TASK [Creation of Docker Containers] *********************************************************************************************************
changed: [shashank-VM] => (item=1)
changed: [shashank-VM] => (item=2)
changed: [shashank-VM] => (item=3)
TASK [Starting Docker Containers] ************************************************************************************************************
changed: [shashank-VM] => (item=1)
failed: [shashank-VM] (item=2) => {"ansible_facts": {"discovered_interpreter_python": "/usr/bin/python"}, "ansible_loop_var": "item", "changed": false, "item": "2", "msg": "Error starting container beb7f1d204f47862d16722f70b812df7193ddacf12d15350a9095cec2ebf4d85: 500 Server Error: Internal Server Error (\"driver failed programming external connectivity on endpoint my-app-2 (880c06fe9e2efa75537e350734be1d46d0cc76e7acf70733d19ad38706dde5ab): Bind for 0.0.0.0:78 failed: port is already allocated\")"}
failed: [shashank-VM] (item=3) => {"ansible_loop_var": "item", "changed": false, "item": "3", "msg": "Error starting container 048f2f3ea6fed5e094fdf59a4650b2b3f8164d804ee7dc8875e6e95bda1300d7: 500 Server Error: Internal Server Error (\"driver failed programming external connectivity on endpoint my-app-3 (8247f75384b240cb9bf1ee66cc9f0404df5465e6c08903304f14bd813c218fa1): Bind for 0.0.0.0:78 failed: port is already allocated\")"}
NOTE : I have an application for which I am building an image and there will be multiple containers running for that image. How do i accessible my application from outside? How do i work on the ports?
Any help is appreciated

Answer 1

The cause of the issue is here:
> Bind for 0.0.0.0:78 failed: port is already allocated
Check what application/container blocks port 78
You can do it with ss:
sudo ss -plunt | grep :78
Or with lsof:
lsof -i :78
Or with fuser:
fuser -v -n tcp 78