sjat
f0d189ca09
Review O1-O3: ADR-017's per-service VERIFY.md requirement now appears in the ADR-004 service-role file table, as a new-role runbook step, and the README docs index/tree are refreshed (ADRs 010-017, security/testing/hardware dirs). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
109 lines
4.7 KiB
Markdown
109 lines
4.7 KiB
Markdown
# ADR-004 — Docker and Compose service model
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## Context
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All services run as Docker containers managed via Docker Compose. This document
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defines how services are structured, deployed, and maintained.
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## Core principles
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- **No hand-edited files on hosts**: all Compose files are rendered by Ansible
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from Jinja2 templates. If a file exists on a host, it was put there by Ansible.
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- **Compose per service**: each service (or tightly coupled service group) gets
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its own Compose file and directory under a standard path.
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- **Variables drive differences**: the same template renders differently per host
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via `group_vars` and `host_vars`. No host-specific templates.
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## Directory layout on hosts
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```
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/opt/services/
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├── servicename/
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│ ├── docker-compose.yml # rendered by Ansible, never edited manually
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│ ├── .env # rendered by Ansible from vault variables
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│ └── data/ # persistent volumes (bind mounts)
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│ └── ...
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```
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All services live under `/opt/services/`. The path is defined in
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`group_vars/all/vars.yml` as `services__base_dir`.
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## Service-role standard
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**Every service has its own self-contained role** — one service, one role. Shared
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roles serving multiple services are no longer used (see "Why not a shared engine"
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below). Each service role contains a standard set of files:
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| File | Purpose |
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|---|---|
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| `tasks/main.yml` | The standard deploy mechanics (below) |
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| `templates/docker-compose.yml.j2` | The Compose definition |
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| `templates/env.j2` | `.env` rendered from vault variables |
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| `defaults/main.yml` | Tuneables, `rolename__` namespace |
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| `README.md` | Purpose, variables, usage (role convention) |
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| `SECURITY.md` | Per-service security record — see ADR-002 and `docs/security/service-security-template.md` |
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| `VERIFY.md` | Per-service UI acceptance spec — see ADR-008 Level 4 / ADR-017 and `docs/testing/service-verify-template.md` |
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| `meta/main.yml`, `molecule/default/` | Metadata + Debian 13 test scenario |
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### Standard deploy mechanics
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Every service role's `tasks/main.yml` follows the same sequence, so all roles are
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uniform and predictable:
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1. Create `/opt/services/<service>/` directory
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2. Render `docker-compose.yml` from `templates/docker-compose.yml.j2`
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3. Render `.env` from `templates/env.j2` (secrets from vault variables)
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4. Run `docker compose up -d --remove-orphans` via `ansible.builtin.command`
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5. Optionally run `docker compose pull` before up (controlled by a variable)
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### Why not a shared engine
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A shared `compose_service` engine role — service roles delegating the mechanics to
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one place — is **intentionally not built**. Duplicating the ~5 standard tasks per
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role is accepted in favour of legible, self-contained roles a reader can understand
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without indirection, and AI authorship makes the duplication cheap to generate
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uniformly from this standard.
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**Revisit trigger:** extract a shared engine role if maintaining the duplicated
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mechanics across service roles becomes painful — a pattern change that means editing
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many roles, or drift between them that this standard alone isn't preventing.
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## Docker daemon configuration
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Managed by the `docker_host` role. Key settings:
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- `"log-driver": "json-file"` with size limits (prevents disk exhaustion)
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- `"iptables": false` — firewall managed entirely by nftables (see ADR-002)
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- TCP socket disabled — Unix socket only (`/var/run/docker.sock`)
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- User namespace remapping: evaluated per use case, not enabled by default
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## Networking
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- Each service Compose file defines its own named network(s)
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- Services that need to communicate are placed on a shared named network
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defined in a dedicated `docker-compose.networks.yml` (if cross-service
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networking is needed on a host)
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- External port publishing is explicit and matches nftables rules
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## Image management
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- Image pinning follows the tiered model in ADR-011: **stateful** services pin
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`tag@digest` (readable tag + integrity digest); **stateless** services use rolling
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tags (`latest`/`stable`), refreshed deliberately and watched by DIUN
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- Bare `latest` is therefore acceptable only on the stateless tier; the stateful tier
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is always pinned
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- Image updates are a deliberate operation: update the tag/digest variable, run deploy
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## Persistent data
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- Bind mounts preferred over named volumes for data that must be backed up
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- All bind mount paths are under `/opt/services/<name>/data/`
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- Backup strategy is defined separately (not in scope of this repo)
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## Decision
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Docker Compose was chosen over Kubernetes/Swarm because:
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- Appropriate complexity level for 2–5 hosts with independent service sets
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- Compose files are human-readable and easily auditable
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- No distributed state to manage
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- Straightforward to back up and restore
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