status: complete audience: both chapter: 02 last_updated: 2026-04 contributors: [alexwill87, claude-cockpit] lang: en

2.4 -- Docker and Docker Compose

Context

Docker runs Vault, PostgreSQL, and potentially other services in isolated containers. Docker Compose orchestrates these containers with a simple YAML file.

Step 1: Install dependencies

$ sudo apt update
$ sudo apt install -y ca-certificates curl gnupg

Step 2: Add the official Docker repository

$ sudo install -m 0755 -d /etc/apt/keyrings
$ curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
$ sudo chmod a+r /etc/apt/keyrings/docker.gpg

$ echo \
  "deb [arch="$(dpkg --print-architecture)" signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu \
  "$(. /etc/os-release && echo "$VERSION_CODENAME")" stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

Step 3: Install Docker Engine

$ sudo apt update
$ sudo apt install -y docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

Step 4: Add the user to the docker group

To avoid typing sudo before each docker command:

$ sudo usermod -aG docker $USER
$ newgrp docker

Step 5: Verify the installation

$ docker --version
$ docker compose version
$ docker run hello-world

Expected result: "Hello from Docker!" in the output.

Note on docker-compose vs docker compose

There are two syntaxes:

This playbook uses exclusively docker compose (with space). If you find tutorials using docker-compose, replace it with docker compose.

Step 6: Configure automatic startup

$ sudo systemctl enable docker
$ sudo systemctl enable containerd

Common errors

• "permission denied" on the Docker socket: You did not add the user to the docker group, or you did not run newgrp docker. Log out and log back in.
• "docker-compose: command not found": You installed Docker from the official repository (good), but you are using the old syntax. Use docker compose (with space).
• Docker installed via snap: Uninstall it (sudo snap remove docker) and reinstall from the official repository. The snap version causes permission issues.

Verification

$ docker ps
$ docker compose version
$ id | grep docker

Expected results: - docker ps runs without error (empty list is normal) - docker compose version displays v2.x.x - The docker group appears in the output of id

Estimated time

10 minutes.