Watchdock

Generic auto-updater for docker compose stacks that deploy GHCR images with immutable tags (e.g. sha-<commit> from docker/metadata-action). Watchtower-style polling, but label-driven and pin-based: deployed tags live in the compose .env file, so deployment state is explicit, auditable, and rollback is a one-line edit.

How it works

Every POLL_INTERVAL seconds, for each labeled service:

1. Query the GitHub Packages API for the newest tag matching TAG_PATTERN
2. If it differs from the pin in .env: pull → update pin → compose up -d <service>
3. If the restart fails, the pin is reverted and the next cycle retries

Services are discovered from the compose file itself — adding a service to the update rotation is just adding labels. No updater config changes.

Dropping into a project

1. Use the prebuilt image ghcr.io/dicodingacademy/watchdock:latest (published by this repo's CI), or copy Dockerfile + updater.sh from the repo root into a directory next to your compose file if you prefer building it yourself.

2. Pin a project name at the top of your compose file (required — without it, compose inside the container resolves a different project and will spawn a duplicate stack):

name: myproject

3. Use variable tags + labels on each service you want auto-updated:

services:
myapp:
image: ghcr.io/myorg/myapp:${MYAPP_TAG:?set in .env}labels:
auto-update.tag-var: MYAPP_TAG # required: name of the pin var in .envauto-update.priority: "10"# optional: lower runs first (default 100)auto-update.tag-pattern: "^sha-[0-9a-f]{7,40}$"# optional: per-service tag regex override

Services without the label are never touched. Dependency services that share a tag var (e.g. a migration job using the same image) should NOT be labeled — they get recreated automatically via depends_on when the labeled service updates.

4. Add the updater service:

updater:
image: ghcr.io/dicodingacademy/watchdock:latest# or, if you copied the files instead:# build: ./updaterenvironment:
GITHUB_TOKEN: ${GHCR_READ_TOKEN:?PAT with read:packages}POLL_INTERVAL: "300"# VERBOSE: "1" # log every check# TAG_PATTERN: "^sha-[0-9a-f]+$" # override tag regex# GHCR_USER: your-github-usernamevolumes:
- /var/run/docker.sock:/var/run/docker.sock
- ./:/composerestart: unless-stoppedlogging:
driver: json-fileoptions:
max-size: "10m"max-file: "3"

5. Seed .env with current tags + the token:

MYAPP_TAG=sha-abc1234
GHCR_READ_TOKEN=ghp_xxxx

6.docker compose up -d updater (add --build if you build it locally)

Configuration reference

See .env.example for a ready-to-copy template.

Env var	Default	Purpose
GITHUB_TOKEN	(required)	PAT with read:packages; also used for GHCR pull
GHCR_USER	token	Username for docker login ghcr.io
COMPOSE_FILE	/compose/docker-compose.yml	Compose file path inside the container
ENV_FILE	/compose/.env	Env file holding the tag pins
POLL_INTERVAL	300	Seconds between cycles
TAG_PATTERN	^sha-[0-9a-f]{7,40}$	Regex for deployable tags
VERBOSE	0	1 = log every check, even when up-to-date

Common Tag Pattern Templates

You can use these common regex patterns in TAG_PATTERN (global env var) or auto-update.tag-pattern (per-service label):

1. Commit SHA Patterns

Tag Format Example	Regex Pattern	Example Output
sha-{commit-sha} (Default)	^sha-[0-9a-f]{7,40}$	sha-a1b2c3d
{commit-sha} (Raw SHA)	^[0-9a-f]{7,40}$	a1b2c3d or a1b2c3d4e5f67890

2. CI/CD Build & Run Patterns

Tag Format Example	Regex Pattern	Example Output
v{run_id}-{commit_sha}	^v[0-9]+-[0-9a-f]{7,40}$	v12345678-a1b2c3d
{run_id}-{commit_sha}	^[0-9]+-[0-9a-f]{7,40}$	12345678-a1b2c3d
build-{number} / release-{number}	`^(build	release

3. Semantic & Calendar Versioning

Tag Format Example	Regex Pattern	Example Output
v{major}.{minor}.{patch} (SemVer)	^v?[0-9]+\.[0-9]+\.[0-9]+$	v1.2.3 or 1.2.3
SemVer with Pre-release (rc, beta)	^v?[0-9]+\.[0-9]+\.[0-9]+(-[a-zA-Z0-9.-]+)?$	v1.2.3-rc.1 or 2.0.0-beta.2
YYYY.MM.DD / YYYY.MM.DD.patch (CalVer)	^v?[0-9]{4}\.[0-9]{2}\.[0-9]{2}(\.[0-9]+)?$	v2026.07.26 or 2026.07.26.1
YYYYMMDD-{commit_sha} (Date + SHA)	^[0-9]{8}-[0-9a-f]{7,40}$	20260726-a1b2c3d

4. Branch & Environment Prefixes

Tag Format Example	Regex Pattern	Example Output
{branch}-{commit_sha}	`^(main	master
{env}-{version}	`^(prod	staging

Tip: You can combine multiple patterns using | (OR), e.g. ^(sha-[0-9a-f]{7,40}|v[0-9]+-[0-9a-f]{7,40})$.

Operations

Rollback: edit the tag var in .env to an older SHA, then docker compose up -d <service>. The updater won't fight you unless a newer version is published to GHCR.

Logs:docker compose logs -f updater. An hourly heartbeat is logged, so silence longer than an hour means something is wrong.

Security note: mounting docker.sock grants this container effective root on the host (standard for this pattern — Watchtower does the same). Keep the PAT minimal-scope (read:packages only).

Requirements

• GHCR images in an org (API path uses /orgs/), private or public
• Immutable tags matching TAG_PATTERN pushed by CI
• PAT with read:packages (SSO-authorized if the org enforces SAML)