When automating server provisioning with Ansible, a common roadblock occurs when trying to execute Docker commands immediately after adding a user to the docker group. Let's examine why this happens:

# Typical Ansible tasks that don't work immediately
- name: Add user to docker group
  user:
    name: "{{ansible_user}}"
    groups: docker
    append: yes

# Subsequent Docker command fails
- name: Build containers
  command: docker-compose build

The fundamental problem stems from how Linux group membership works. When you add a user to a new group:

• The change writes to /etc/group immediately
• Existing sessions won't recognize the new membership
• Only new login sessions will have the updated group permissions

Method 1: Using newgrp with Shell Module

- name: Refresh group membership
  shell: newgrp docker
  args:
    executable: /bin/bash

- name: Verify access
  command: docker ps

Method 2: Create a New SSH Connection

- name: Force new SSH connection
  meta: reset_connection

- name: Build containers (now with proper permissions)
  command: docker-compose build

Method 3: Temporary Workaround with Become

- name: Run as root temporarily
  become: yes
  command: docker-compose build

The cleanest approach involves splitting your playbook into separate plays with distinct connections:

- hosts: servers
  tasks:
    - name: Add to docker group
      user:
        name: "{{ansible_user}}"
        groups: docker
        append: yes

- hosts: servers
  gather_facts: no
  tasks:
    - name: Build containers
      command: docker-compose build

async with Polling /h2>

For more complex scenarios where you need to ensure the group change propagates:

- name: Add to docker group
  user:
    name: "{{ansible_user}}"
    groups: docker
    append: yes
  async: 10
  poll: 0
  register: group_add

- name: Wait for group propagation
  async_status:
    jid: "{{ group_add.ansible_job_id }}"
  register: job_result
  until: job_result.finished
  retries: 5

When automating server setups with Ansible, a common pain point emerges when dealing with freshly added user groups. The scenario typically looks like this:

- name: Add user to docker group
  user:
    name: "{{ ansible_user }}"
    groups: docker
    append: yes

Followed immediately by Docker commands that fail because the SSH session maintains the old group membership cache.

Linux systems don't automatically refresh group membership for existing sessions. The kernel maintains the credential cache for each process, including SSH sessions. While the /etc/group file gets updated immediately, running processes (like your Ansible SSH connection) won't see the changes until they re-establish their session.

Solution 1: New SSH Connection with Meta Module

The cleanest approach is to force Ansible to establish a fresh connection after group modification:

- name: Add user to docker group
  user:
    name: "{{ ansible_user }}"
    groups: docker
    append: yes

- name: Refresh connection
  meta: reset_connection

- name: Now Docker commands will work
  command: docker ps

Solution 2: Temporary Shell Workaround

For environments where resetting connections isn't feasible:

- name: Execute Docker commands with fresh login shell
  shell: |
    sg docker -c "docker-compose build --pull"
  args:
    chdir: /docker

Solution 3: Become with Explicit Login Shell

Using su -l for a proper login session:

- name: Build with fresh environment
  become: yes
  become_user: "{{ ansible_user }}"
  become_method: su
  become_flags: -l
  command: docker-compose build --pull
  args:
    chdir: /docker

For complex playbooks, consider this pattern:

- block:
    - name: Ensure docker group exists
      group:
        name: docker
        state: present

    - name: Add user to docker group
      user:
        name: "{{ ansible_user }}"
        groups: docker
        append: yes

  always:
    - name: Reset connection if changed
      meta: reset_connection
      when: ansible_user is changed